Enzyme Inhibitor – Enzymes and Enzyme Kinetics | Lecturio

00:16:14
https://www.youtube.com/watch?v=sDeqx9Zk9ew

概要

TLDRThe lecture discusses enzyme inhibition, differentiating between reversible and irreversible inhibitors. Reversible inhibitors include competitive, non-competitive, and uncompetitive inhibitors, each with distinct properties and effects on enzyme kinetics. Competitive inhibitors mimic substrates and compete for active sites, affecting the enzyme's affinity (Km) without altering Vmax. Non-competitive inhibitors bind elsewhere, reducing Vmax but leaving Km unchanged, while uncompetitive inhibitors bind to the enzyme-substrate complex, ultimately lowering both Vmax and Km. Irreversible inhibition, such as suicide inhibition, involves covalent binding that permanently inactivates the enzyme, exemplified by penicillin's action on bacterial cell wall synthesis. Understanding these mechanisms is crucial for drug development.

収穫

  • 🔍 Understanding enzyme inhibition is crucial for drug design.
  • ⚙️ Competitive inhibition involves substrate-like inhibitors.
  • 📉 Non-competitive inhibitors lower Vmax but not Km.
  • ⚠️ Uncompetitive inhibitors only bind to the enzyme-substrate complex.
  • 🧪 Suicide inhibition leads to irreversible enzyme inactivation.

タイムライン

  • 00:00:00 - 00:05:00

    This lecture discusses how understanding enzyme inhibition is crucial for both enzymatic mechanisms and medical applications. The focus is on reversible enzyme inhibitors—specifically competitive, non-competitive, and uncompetitive inhibition—as well as irreversible inhibitors. Enzymes catalyze reactions fundamental for cellular functions, and inhibiting these enzymes can help control diseases like bacterial infections and cancer by stopping cell division or growth.

  • 00:05:00 - 00:10:00

    The lecture explains competitive inhibition, where an inhibitor mimics the substrate and competes for the enzyme's active site, affecting the enzyme's function but not its maximum velocity (V-max). The presence of a competitive inhibitor increases the apparent Km value (indicating reduced affinity), while at high substrate concentrations, the inhibitor's influence diminishes, leading to eventual similarity in V-max to uninhibited reactions. A Lineweaver-Burk plot is used to illustrate these effects graphically.

  • 00:10:00 - 00:16:14

    Non-competitive inhibition is then explored, contrasting it with competitive inhibition by discussing how a non-competitive inhibitor binds to an alternate site on the enzyme, preventing substrate processing without competing for the active site. This reduces the effective V-max but does not affect Km. Lastly, uncompetitive inhibition is described as it selectively binds to the ES complex, altering both V-max and Km values. The concept of suicide inhibition is introduced as a form of irreversible inhibition where the inhibitor binds covalently, permanently inactivating the enzyme, such as penicillin's mechanism against bacterial cell wall synthesis.

マインドマップ

ビデオQ&A

  • What is competitive inhibition?

    Competitive inhibition occurs when an inhibitor resembles the substrate and competes for the active site of an enzyme, preventing the substrate from binding.

  • How does non-competitive inhibition work?

    Non-competitive inhibition involves an inhibitor binding to a different site on the enzyme, reducing its activity regardless of substrate concentration.

  • What is the difference between Km and Vmax?

    Km is the substrate concentration at which the reaction velocity is half of Vmax, indicating the enzyme's affinity for the substrate, while Vmax is the maximum rate of reaction.

  • What is uncompetitive inhibition?

    Uncompetitive inhibition occurs when an inhibitor binds only to the enzyme-substrate complex, preventing it from converting to product.

  • What is suicide inhibition?

    Suicide inhibition is a form of irreversible inhibition where the inhibitor forms a covalent bond with the enzyme, permanently disabling it.

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  • 00:00:00
    [Music]
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    understanding how enzymes are inhibited
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    has important implications both for our
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    understanding of the mechanism of
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    enzymatic action and with medical
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    considerations in this lecture I will
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    talk about two primary things reversible
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    enzyme inhibitors and also irreversible
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    enzyme inhibitors cells of course rely
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    on enzymes to catalyze reactions and
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    that reliance on enzymes allows us to be
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    able to control cells if we can control
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    enzymes and that means it's a
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    consideration particularly if we have a
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    bacterium for example that we want to
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    stop from infecting something or a
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    cancer cell that we want to stop from
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    spreading
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    so inhibiting enzymes is an important
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    consideration for us for health purposes
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    I want to spend some time talking about
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    three different types of inhibition of
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    enzymes and the first of these that I'll
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    talk about is called competitive
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    inhibition you can see this shown
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    schematically on the screen the enzyme
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    with its normal substrate as shown on
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    the left the enzyme binds to the
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    substrate and converts the substrate
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    into product on the right we see that
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    same enzyme that is the target of an
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    inhibitor of it and in this case the
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    target inhibitor looks like the original
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    substrate it fits in the active site of
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    the enzyme the same way that the the
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    normal substrate did but there's
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    something about the inhibitor that the
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    enzyme can't manipulate it can't do
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    anything with it and that causes the
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    enzyme to sorta sit and spin its wheels
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    while it's bound to that inhibitor that
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    inhibitor is called a competitive
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    inhibitor and a competitive inhibitor
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    has the properties I've shown here that
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    it looks like the substrate and binds to
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    the active site now on the screen here
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    you can see a couple of different
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    molecules the bottom molecule is a
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    molecule that's used by an enzyme called
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    dihydrofolate reductase the enzyme
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    dihydrofolate reductase uses this
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    molecule and converts it into a product
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    where the product is used to make
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    nucleotides very important for
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    nucleotides the molecule above it is
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    called methotrexate and methotrexate is
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    very similar to dye head to
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    dihydrofolate however
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    there's an important difference to it
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    and the difference prohibits the enzyme
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    dihydrofolate reductase from acting
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    while methotrexate is an inhibitor of
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    that enzyme and by inhibiting an enzyme
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    that makes nucleotides that specific for
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    a cell one could imagine that one could
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    stop that self from dividing and that's
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    exactly what this inhibitor is used for
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    now let's study the effects of that
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    competitive inhibitor on an enzyme if we
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    take an enzyme and we compare the V
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    versus s plot of an uninhibited reaction
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    with an inhibited reaction we will get
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    something like what we see on the screen
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    here now I need to explain how this was
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    done I've described how we used say 20
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    tubes to generate the data that's used
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    to make the first line that is that the
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    enzyme plus varying amounts of substrate
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    each tube has a different amount of
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    substrate and a buffer are used and we
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    measure the velocity by measuring the
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    amount of products the quantity
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    concentration of products produced over
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    time if we want to study the inhibitor
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    we want the the inhibited reaction we
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    want to remember that we want to have
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    one variable and the one variable we
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    said we have is substrate concentration
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    that means that we can't vary the amount
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    of inhibitor so when we cheat we do the
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    second set of reactions we have the same
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    amount of enzyme we have the same buffer
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    and we have the same amount of inhibitor
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    in each tube but we have varying amounts
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    of substrate what happens when we do
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    that well when we do that we see that
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    the reaction starts off and it's at a
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    lower rate that's not too surprising
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    because there's inhibitor there that's
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    inhibiting enzyme the velocity is lower
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    but as we go to increasing amounts of
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    substrate we see that the inhibitor
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    keeps rising and rising and rising and
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    by the end it's actually rising fast
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    enough that it is getting in the range
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    of the velocity of the uninhibited
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    reaction okay we see that this the the
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    difference between the two curves is
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    decreasing now I'll cut to the chase
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    here and I'm cutting to the chase I'll
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    tell you that if we go to very very
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    large amounts of substrate we will
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    discover that the two enzymes have the
  • 00:04:13
    same v-max now why is that the case why
  • 00:04:16
    does a competitively inhibited reaction
  • 00:04:19
    have the same v-max as an as no
  • 00:04:22
    inhibitor whatsoever
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    the answer is due to the way that the
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    experiment was set up I said that we had
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    fixed amount of inhibitor it gigantic
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    concentrations of substrate what happens
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    well the substrate it's much more likely
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    that the substrate will be found by the
  • 00:04:37
    enzyme then the inhibitor will be found
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    by the enzymes at low concentrations
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    they compete pretty well but at high
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    concentrations where I might have a
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    million times as much substrate as I
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    have inhibitor the difference between
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    the uninhibited and the inhibited is
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    difficult for me to see in addition to
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    the v-max not changing for the a
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    competitively inhibit of reaction
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    something does change in this reaction
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    and the thing that changes is the km
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    since the two reactions that is the
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    uninhibited and the inhibited reaction
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    have the same v-max they have the same
  • 00:05:09
    v-max over two so if we plot on each
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    curve the km value which we get from
  • 00:05:15
    v-max over two we discover that the km
  • 00:05:17
    value for the uninhibited reaction is as
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    we would expect but the km for the
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    competitively inhibit of reaction
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    increases now that increase is
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    indicating an apparent change in the
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    affinity of the enzyme for the substrate
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    now that I say apparent because it
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    doesn't actually change the affinity of
  • 00:05:35
    the enzyme for the substrate and that's
  • 00:05:36
    a deeper topic that I'll talk about here
  • 00:05:38
    but the apparent km increases making it
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    seeing that the enzyme is losing its
  • 00:05:43
    affinity for its substrate this is shown
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    graphically in another way using a
  • 00:05:48
    lineweaver-burk plot so remember with a
  • 00:05:50
    lineweaver-burk we take the same data
  • 00:05:52
    that we had for the V versus s plot and
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    we invert all the data and then plot
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    that on an inverted plot as you see here
  • 00:05:58
    one over V zero versus one over the
  • 00:06:00
    concentration of s when we do that we
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    see that not surprisingly the V versus s
  • 00:06:06
    data comes to a line is shown in green
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    with a y-intercept corresponding to 1
  • 00:06:11
    over v-max and an x intercept
  • 00:06:13
    corresponding to minus 1 over km when we
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    plot the competitive inhibitor we see
  • 00:06:18
    exactly what we learned in the last plot
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    which was that the v-max is the same and
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    the two lines cross at the y axis and
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    since the km value increased for the
  • 00:06:28
    competitive inhibition what we see then
  • 00:06:31
    is that the minus 1 over km gets closer
  • 00:06:33
    to zero the lineweaver-burk plot shows
  • 00:06:36
    us very graphically what's happening
  • 00:06:38
    with that inhibition another type of
  • 00:06:40
    inhibition that's
  • 00:06:41
    important for us to understand is that
  • 00:06:42
    of non-competitive inhibition it's
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    fundamentally different from in
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    competitive inhibition and we can see it
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    depicted on the screen here on the left
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    again we have the enzyme with its normal
  • 00:06:51
    substrate which catalyzes a reaction
  • 00:06:53
    however the enzyme has a site on it that
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    if is properly targeted by an inhibitor
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    the inhibitor can bind to it and keep
  • 00:07:02
    the enzyme from functioning properly
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    with the substrate in the active site
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    and that's shown in the image on the
  • 00:07:08
    right now when this happens the
  • 00:07:10
    non-competitive inhibitor has a
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    fundamentally different way of
  • 00:07:14
    interacting with the enzyme than what we
  • 00:07:16
    saw before they affect it by binding at
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    a different location and by binding at a
  • 00:07:20
    different location they do not compete
  • 00:07:24
    okay now this changes the parameters of
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    the things that we've been sities that
  • 00:07:30
    we've been studying considerably and
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    because the to inhibit err does not
  • 00:07:35
    compete with the substrate and the
  • 00:07:37
    substrate can't out weigh it by adding
  • 00:07:39
    an awful lot more sub by doing a
  • 00:07:41
    reaction with an awful lot more
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    substrate it means that in every
  • 00:07:44
    reaction that we do what happens is that
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    we're inhibiting a fixed amount of
  • 00:07:49
    enzyme it doesn't matter how much enzyme
  • 00:07:52
    that we add there's always the same
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    amount of enzyme inhibited in the first
  • 00:07:57
    reactions the competitively inhibited
  • 00:07:59
    reactions we saw that as we added more
  • 00:08:01
    substrate the substrate how competed the
  • 00:08:04
    inhibitor and it was as if the inhibitor
  • 00:08:06
    disappeared so the quantity of enzyme
  • 00:08:08
    being inhibited was changing the more
  • 00:08:11
    substrate we added the more normal
  • 00:08:14
    enzyme we had with a non-competitive
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    inhibitor we don't have that it doesn't
  • 00:08:19
    matter how much substrate we have
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    because they're not competing for the
  • 00:08:22
    same site the non-competitive inhibitor
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    is always going to knock out the same
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    amount of enzyme in every tube
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    irrespective of how much substrate is
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    added to it that means that we've
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    changed the amount of enzyme and if we
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    change the amount of enzyme we've
  • 00:08:39
    already talked about the limitations of
  • 00:08:40
    an enzyme and studying it with v-max
  • 00:08:43
    remember the factory analogy and the
  • 00:08:45
    factory analogy I said that if we added
  • 00:08:48
    an extra factory would double the amount
  • 00:08:50
    of product what if the factory only
  • 00:08:53
    worked half a day
  • 00:08:54
    if the factory only worked half a day it
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    would make half the amount of product
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    we've changed the numbers of workers so
  • 00:09:00
    what if we use enough inhibitor that we
  • 00:09:03
    only have half the amount of enzyme well
  • 00:09:06
    we would change v-max accordingly so
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    when we have a non-competitive inhibitor
  • 00:09:09
    we're changing the amount of enzyme and
  • 00:09:12
    then changing the amount of enzyme we
  • 00:09:14
    change the value of V Max so v-max
  • 00:09:17
    decreases for a non-competitive
  • 00:09:20
    inhibitor that wasn't the case for a
  • 00:09:22
    competitive inhibitor right now we can
  • 00:09:25
    only measure km for an active enzyme and
  • 00:09:27
    not surprisingly if we change the amount
  • 00:09:30
    of enzyme km the affinity the enzyme for
  • 00:09:33
    the substrate doesn't change because the
  • 00:09:35
    enzyme is still the enzyme when it's
  • 00:09:37
    active and we're only studying active
  • 00:09:39
    enzyme so the km value does not change
  • 00:09:42
    for non-competitive inhibition on a
  • 00:09:46
    lineweaver-burk plot we see something
  • 00:09:48
    different than we saw with a competitive
  • 00:09:49
    inhibition but consistent with what I
  • 00:09:52
    just told you in green again we see the
  • 00:09:54
    linear a lot the linear plot showing of
  • 00:09:57
    course the uninhibited reaction in blue
  • 00:10:00
    we see the non competitively inhibited
  • 00:10:03
    reaction and we noticed that the two
  • 00:10:04
    lines crossed at minus 1 over km well
  • 00:10:08
    this is consistent with what we learned
  • 00:10:09
    in the last plot which is that the km
  • 00:10:11
    value does not change they should cross
  • 00:10:13
    at that point however we see the blue
  • 00:10:15
    line is has a higher slope than does the
  • 00:10:19
    Green Line meaning that the crossing of
  • 00:10:22
    the y-axis is at a higher point now that
  • 00:10:26
    may seem counterintuitive that if we
  • 00:10:28
    decrease the v-max we actually are
  • 00:10:30
    raising the value of that line but
  • 00:10:32
    remember we're doing a reciprocal so by
  • 00:10:35
    decreasing v-max 1 over v-max actually
  • 00:10:38
    increases okay now the last plot the
  • 00:10:42
    last inhibition I want to do is one
  • 00:10:44
    that's a little harder to get your head
  • 00:10:45
    around and I mainly want to just
  • 00:10:46
    introduce what it does and the effects
  • 00:10:49
    of this inhibitor this inhibitor type of
  • 00:10:52
    inhibition is called uncompetitive and
  • 00:10:54
    uncompetitive is somewhere in between
  • 00:10:56
    the two a uncompetitive Utley inhibited
  • 00:11:00
    reaction occurs by a mechanism that you
  • 00:11:02
    see on the screen the normal substrate
  • 00:11:04
    binds to an enzyme as before but in the
  • 00:11:07
    case of the uncompetitive
  • 00:11:08
    inhibitor it only binds to the es
  • 00:11:11
    complex now that es complex is on the
  • 00:11:16
    way to becoming product and so it's only
  • 00:11:20
    binding at that point so the more es
  • 00:11:21
    complex we have which is what we're
  • 00:11:24
    gonna have with more substrate the more
  • 00:11:26
    es complex we have the more inhibited
  • 00:11:29
    enzyme that we have now that's kind of
  • 00:11:31
    hard to get our heads twisted around
  • 00:11:32
    we're gonna see in fact as we look at
  • 00:11:34
    the plots if that's going to be
  • 00:11:35
    difficult to conceptualize as well let's
  • 00:11:39
    take a look at the kinetics now of an
  • 00:11:40
    uncompetitive reaction compared to that
  • 00:11:42
    of an uninhibited reaction again we're
  • 00:11:45
    plotting V versus s we as we have done
  • 00:11:46
    before the orange plot is the
  • 00:11:49
    uninhibited reaction no inhibitor
  • 00:11:51
    present and we see a normal a hyperbolic
  • 00:11:53
    plot when we plot the uncompetitive
  • 00:11:56
    inhibited reaction however we see
  • 00:11:58
    something that's a little hard to get
  • 00:11:59
    our heads around the problem are the the
  • 00:12:02
    confusion with the uncompetitive
  • 00:12:03
    reaction is that first of all we see
  • 00:12:05
    that it has a lower apparent v-max and
  • 00:12:07
    it does have a lower apparent v-max and
  • 00:12:09
    the other thing that's confusing about
  • 00:12:11
    this is it has a slightly higher
  • 00:12:14
    velocity at lower concentrations and
  • 00:12:18
    that happens actually because the
  • 00:12:19
    uncompetitive inhibitor favors the es
  • 00:12:22
    complex it says if we are increasing the
  • 00:12:24
    percentage of the enzyme present in the
  • 00:12:28
    es complex and that has the effect of
  • 00:12:31
    apparently speeding up the reactions
  • 00:12:33
    which is why that first part of the
  • 00:12:34
    curve the velocity for the uncompetitive
  • 00:12:38
    reaction is higher than it is for the
  • 00:12:40
    the the reaction with no competitor well
  • 00:12:43
    when we do the plots we also see
  • 00:12:45
    something interesting that happens and
  • 00:12:47
    that is that the uncompetitive reaction
  • 00:12:49
    has a lower km value so not only does
  • 00:12:53
    the uncompetitive reaction at high
  • 00:12:55
    substrate concentrations have a lower
  • 00:12:57
    velocity because at higher substrate
  • 00:12:59
    concentrations will have a greater
  • 00:13:01
    percentage of the enzyme in es complex
  • 00:13:03
    which is greater target for the
  • 00:13:04
    uncompetitive inhibitor but we also see
  • 00:13:07
    that the apparent km of the enzyme is
  • 00:13:10
    decreased and again this happens because
  • 00:13:12
    the the inhibitor is favoring the es
  • 00:13:16
    complex it's making it look like the
  • 00:13:18
    enzyme is binding substrate better well
  • 00:13:21
    that can
  • 00:13:22
    using result is reflected in what we see
  • 00:13:24
    on a lineweaver-burk plot on the
  • 00:13:27
    lineweaver-burk plot what we have is
  • 00:13:29
    something that looks like this the Green
  • 00:13:32
    Line again shows the uninhibited
  • 00:13:33
    reaction with what we've seen before the
  • 00:13:36
    one over v-max the intercept on the y
  • 00:13:39
    axis and the minus one over km on the x
  • 00:13:41
    axis the lineweaver-burk plot for the
  • 00:13:44
    uncompetitive reaction shows a value
  • 00:13:46
    higher on the y axis for one of our
  • 00:13:49
    v-max and that's reflective of the fact
  • 00:13:51
    that the v-max has decreased so one of
  • 00:13:53
    our v-max has increased and we also see
  • 00:13:56
    the x axis has moved farther to the left
  • 00:13:59
    meaning minus one over km has farther
  • 00:14:01
    away from zero which is what happens
  • 00:14:03
    when we have a lower km the three
  • 00:14:07
    mechanisms of enzyme inhibition that
  • 00:14:09
    I've talked about so far competitive
  • 00:14:11
    inhibition non-competitive inhibition
  • 00:14:12
    and uncompetitive inhibition are
  • 00:14:15
    fundamentally different from the one I'm
  • 00:14:16
    getting ready to talk about here in each
  • 00:14:18
    of those cases the binding of the
  • 00:14:20
    inhibitor to the enzyme was a reversible
  • 00:14:22
    process the inhibitor could go on but
  • 00:14:24
    the inhibitor could also come off and
  • 00:14:26
    these are very common inhibition
  • 00:14:27
    mechanisms the mechanism getting ready
  • 00:14:29
    to describe here called suicide
  • 00:14:31
    inhibition is different completely from
  • 00:14:33
    them in suicide inhibition what happens
  • 00:14:36
    is the inhibitor that binds to the
  • 00:14:38
    enzyme does so irreversibly and it does
  • 00:14:41
    it irreversibly because the inhibitor
  • 00:14:43
    makes a covalent bond with the enzyme at
  • 00:14:45
    the active site the enzyme can't shake
  • 00:14:48
    the sub that the inhibitor loose and as
  • 00:14:50
    a consequence the enzyme is completely
  • 00:14:52
    put out of action now example of a
  • 00:14:55
    reaction like this occurring is that of
  • 00:14:56
    the action of penicillin which use which
  • 00:14:59
    we use to kill bacteria penicillin works
  • 00:15:01
    because what it does is it inhibits the
  • 00:15:03
    the bacterium's ability to make cell
  • 00:15:05
    walls well cell walls are pretty
  • 00:15:07
    important for cells because without a
  • 00:15:09
    wall you don't have a cell the way that
  • 00:15:11
    this works is penicillin mimics the
  • 00:15:13
    normal substrate that the enzyme that
  • 00:15:16
    makes the cell walls uses that's the
  • 00:15:17
    Pedigo icing chain because penicillin
  • 00:15:20
    resembles that the enzyme binds to it
  • 00:15:21
    like it would bind to the normal
  • 00:15:23
    substrate but penicillin makes the
  • 00:15:24
    covalent bond
  • 00:15:25
    so in suicide inhibition the enzyme is
  • 00:15:28
    completely destroyed and never gets a
  • 00:15:30
    chance to come back into its thing well
  • 00:15:32
    in this
  • 00:15:33
    of lectures what I have talked about are
  • 00:15:35
    different types of inhibition a
  • 00:15:37
    reversible set of inhibitions that
  • 00:15:38
    included a competitive non-competitive
  • 00:15:40
    and uncompetitive and now suicide
  • 00:15:42
    inhibition that is an irreversible
  • 00:15:44
    enzyme inhibition our understanding of
  • 00:15:46
    enzyme inhibition is important for
  • 00:15:48
    anyone interested in understanding the
  • 00:15:50
    mechanism by which drugs work or
  • 00:15:51
    designing drugs themselves
  • 00:16:03
    you
  • 00:16:05
    [Music]
タグ
  • enzymes
  • inhibition
  • competitive
  • non-competitive
  • uncompetitive
  • suicide inhibition
  • enzyme kinetics
  • Vmax
  • Km
  • pharmacology