Michaelis-Menten Kinetics: Considerations – Enzyme Classification

by Kevin Ahern, PhD

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    00:01 The rates of enzymatic reaction and the affinity enzymes have for their substrates are important concepts to understand.

    00:07 I will deal with these topics in the first part of this presentation covering data analysis.

    00:12 I will also talk about allosterism and the affect it has on enzymes and their catalysis.

    00:18 Next I will talk about substrate binding and how that can happen in different mechanisms within enzymes.

    00:23 And last I will talk about the way that we classify enzymes and understand reactions in a very much broad sense.

    00:31 Okay under Michaelis-Menten Kinetics, we learned that it's important for us to study enzymatic reactions or the conditions where our study states. That is we have relatively constant amounts of ES complex.

    00:44 Under Michaelis-Menten Kinetics, the equation on the top applies and this equation tells us some important things that we are going to learn in this lecture.

    00:52 Now Vo that is the velocity of a reaction is equal to Vmax and that's something that we will discuss in a moment, times the concentration of substrate divided by another quantity called Km, that we will discuss, plus the concentration of substrate.

    01:05 So we have learned two terms here that are gonna become important for us to understand and that's Vmax, the maximum velocity of a reaction and Km which is a quantity that allows us to measure the affinity that an enzyme has for its substrate.

    01:20 Well, first let's start with Vmax. With Vmax, it's important to understand what it is, and why it is and how that happens.

    01:28 We saw when we plotted Vo versus the concentration of sustrate below, that, we saw that the curve grew and then it leveled off.

    01:38 And the reason it levels off is due to the way that enzyme work and the way that they interact with substrates.

    01:44 Instead of an enzymatic reaction going and staying linear with increasing concentrations of substrate, what happens is enzymes get saturated with substrate.

    01:55 Saturation of substrate means that the enzyme binds almost constantly bound substrate, meaning that we have almost everything in the ES complex.

    02:06 So at very high substrate concentrations the enzyme is continually releasing product.

    02:15 And over time if we add more and more substrate we exceed the capacity of the enzyme to bind more substrate.

    02:21 So under saturating conditions of substrate, the enzyme is no longer able to stay linear, and it flattens off. So we see this hyperbolic plot.

    02:32 Now an example might be a factory that is making products. A factory that's making products will have a lot of workers.

    02:38 And those workers are working on something but if they don't have enough materials to make product, then the workers are gonna be standing around for fair amount of time waiting for material so they can make product.

    02:49 On the other hand we could imagine that if we have those same workers working and they have all the materials they need to make products, they are gonna turn out a certain number of products per day.

    03:01 If we increase the amount of materials but we don't increase the number of workers we are not gonna change that maximum amount they are going to get. So we see the same thing happening in the real world that we see happening with enzymatic reactions.

    03:14 If we want to the increase the amount of product we have to get more workers, perhaps get another factory in order to make more product.

    03:23 Now enzymes that don't follow Michaelis-Menten Kinetics, and there are some, include those that bind substrates cooperatively.

    03:30 Now in another presentation I talked about how hemoglobin binds to oxygen cooperatively.

    03:36 And that means that the binding of one substrate is affecting the binding of others.

    03:42 So when this happens, and of course this only happens for multisubunit proteins, when this happens, when the binding of one affects the others, then of course we are going to see a change in the velocity; because, that's going to change the actual binding conditions of the enzyme.

    03:57 When we have those things happen we can tell them pretty easily; because, what we will get is an "S" shape curve for the V versus S plot, very much like what we saw with the hemoglobin binding to oxygen.

    About the Lecture

    The lecture Michaelis-Menten Kinetics: Considerations – Enzyme Classification by Kevin Ahern, PhD is from the course Enzymes and Enzyme Kinetics.

    Included Quiz Questions

    1. Hyperbolic plot
    2. Linear plot
    3. Parabolic plot
    4. Sigmoidal curve
    5. U-shaped plot
    1. The affinity of the enzyme for its substrate
    2. The affinity of the enzyme for the final product
    3. The velocity of the reaction at steady state
    4. The rate of reaction at the initial phase of reaction at higher substrate concentrations
    5. The rate of reverse reaction

    Author of lecture Michaelis-Menten Kinetics: Considerations – Enzyme Classification

     Kevin Ahern, PhD

    Kevin Ahern, PhD

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    Perfectly explained!
    By marcus o. on 26. February 2019 for Michaelis-Menten Kinetics: Considerations – Enzyme Classification

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    By Hazazi M. on 04. October 2018 for Michaelis-Menten Kinetics: Considerations – Enzyme Classification

    Professor Ahern is a perfect teacher and he makes everything so easy to understand

    I understood perfectly the concepts the way he explained them
    By Yainely V. on 26. September 2017 for Michaelis-Menten Kinetics: Considerations – Enzyme Classification

    I understood perfectly the concepts the way he explained them. He makes it ease to grasp