Enzyme Kinetics - Online Tutor, Practice Problems & Exam Prep

Enzyme kinetics measures the relationship between substrate concentration and enzyme reaction speed. Key metrics include V_max, the maximum reaction velocity at saturated substrate levels, and K_m, the Michaelis constant, indicating substrate concentration at half V_max. A low K_m suggests tight enzyme-substrate binding, while a high K_m indicates weak binding. Understanding these concepts is crucial for analyzing enzyme efficiency and reaction rates in biochemical processes.

Kineticss

Hi. In this video, we're going to be talking about enzyme kinetics. So what are enzyme kinetics? Well, enzyme kinetics actually measure the activity of an enzyme. This refers to measuring the relationship between the substrate concentration and the speed of enzyme reactions. It depends on the concentration of the substrate. I've prepared for you two different potential ways reactions can occur. So the first is if there's a low substrate concentration, that means there are fewer collisions, and therefore the substrate is rate-limiting. So, if we look at this example here, let me back out of the way. You can see that if there's a low amount of substrate, so here there are a ton of enzymes, there are going to be only a few collisions between substrate and enzyme. Therefore, we say the substrate is rate-limiting, which means that the substrate is controlling the rate of the reaction.

Now, if we go to the second potential occurrence, and that is if there's a high substrate concentration, then there are more collisions between enzyme and substrates and the enzyme is rate-limiting. So this is actually over here, so you can see there's a ton of substrates. There's a high substrate concentration, so there are more collisions. And that means that the enzyme is rate-limiting because all of the enzymes are bound, and so there can't be more reactions than there are enzymes to catalyze the reaction. Enzyme kinetics really deals with looking at these two different reactions. How much substrate, how much enzyme is there, so how fast can the reaction occur? Generally, enzyme kinetics is a measure that is taken before any product has been formed. That way we can actually look and see how fast the reaction is going to occur before it actually gets started. So, now let's move on.

Kinetic Measurements

So how do we measure enzyme kinetics? Well, we do this through these 2 values here, the V_max and the K_M. And the K_M is also called the Michaelis constant. You'll see the Michaelis-Menten equation maybe come up in your textbook, and so this is what we're talking about here. And, these two measures are the measure of enzyme performance. So, what do each of them measure? Well, the V_max measures the velocity or the speed of the enzyme reaction. This depends on the substrate concentration, obviously. So, as the substrate concentration gets higher and becomes more saturated, this is when the upper level of reactivity is met. So again, high substrate concentrations lead to more collision between enzyme and substrate; the enzyme is rate-limiting. In these situations, when the substrate concentration is saturated, that is when you want to measure V_max, because that's going to be the fastest way the reaction occurs. If we have so many substrates, all of the enzymes are filled, and so they're acting maximally to speed up the reaction as fast as possible.

Now, this is different from the K_M, which actually measures enzyme function by determining the concentration of substrate needed to work at half V_max. Depending on what half V_max is, the K_M measures how tightly the enzyme and substrate are bound. So, a small K_M means the enzyme binds tightly, whereas a large K_M means the enzyme binds weakly. These values can be used to calculate what's known as the turnover number, which is how rapidly a substrate molecule can undergo a reaction. So now let's look at these relationships via an actual image, which I think becomes easier to conceptualize this.

On the y-axis, we actually have reaction velocity speed. So this is occurring faster. And then we have a substrate concentration, which again is increasing on the x-axis. So we have V_max here, we have half V_max and V_max. And, V_max is going to be the speed of the reaction when the substrate is saturated. So, all the enzymes have substrate bound to them, and there is an excess of substrate; how fast can the reaction occur? Which here is going to be this number. Now, the K_M is looking at what is the amount of substrate bound at half V_max. So, half V_max is here, at this this point here. And, so, how much substrate is bound, we follow the line and we go down. So, the amount of substrate bound is here. So, amount substrate bound at 1 half V_max. Now remember, I said that you can use the K_M value to determine how tightly the enzyme is binding. Well, we can do this because if the half V_max is fairly low, then we know or the concentration of the substrate needed to create half V_max is fairly low, but we know the enzyme is working very well. It's binding tightly, doing its thing, and releasing it. Binding tightly, doing its thing, so, it's happening quickly. Whereas, if the concentration is really high, say here for instance, and half V_max is here, then we can say, okay. Well, the enzyme is actually binding fairly loosely, and it's not being very efficient at what it's doing. And, therefore, you know, it's not efficient. It's binding loosely. And, so, the substrate concentration needed to make half V_max is actually really high. And so that's the relationship between V_max, K_M, and the concentration of substrates. So now, let's move on.

If an enzyme is determined to have a low Km what does that say about the reaction?

• A. The enzyme binds loosely to the substrate
• B. That the speed of the reaction is slow
• C. The enzyme binds tightly to the substrate
• D. That the speed of the reaction is fast

Which of the following terms describes how rapidly a substrate can undergo a reaction?

• A. Kinetics
• B. Turnover Number
• C. Saturation Rate
• D. Reaction Speed

Here’s what students ask on this topic:

What is enzyme kinetics and why is it important?

Enzyme kinetics is the study of the rates of enzyme-catalyzed reactions. It involves measuring the relationship between substrate concentration and the speed of the reaction. This field is crucial because it helps us understand how enzymes work, how they can be regulated, and how they interact with substrates. By analyzing enzyme kinetics, scientists can determine the efficiency of enzymes, identify potential inhibitors, and design drugs that can modulate enzyme activity. Key metrics in enzyme kinetics include Vmax (maximum reaction velocity) and Km (Michaelis constant), which provide insights into enzyme performance and substrate binding affinity.

What is the Michaelis-Menten equation and what does it describe?

The Michaelis-Menten equation describes the rate of enzymatic reactions by relating reaction velocity (v) to substrate concentration ([S]). The equation is given by:

$v=\frac{V{\max }_{}\cdot S}{K{m}_{}+S}$

Here, Vmax is the maximum reaction velocity, and Km is the Michaelis constant, which indicates the substrate concentration at half Vmax. This equation helps in understanding how changes in substrate concentration affect the reaction rate and provides insights into enzyme efficiency and substrate binding affinity.

What is Vmax in enzyme kinetics?

Vmax, or maximum reaction velocity, is a key parameter in enzyme kinetics. It represents the fastest rate at which an enzyme can catalyze a reaction when the substrate concentration is saturated. At Vmax, all enzyme active sites are fully occupied by substrate molecules, and the reaction rate is at its peak. Vmax is crucial for understanding the catalytic efficiency of an enzyme and is used in conjunction with the Michaelis constant (Km) to characterize enzyme behavior under different conditions.

What does a low Km value indicate about an enzyme's affinity for its substrate?

A low Km value indicates that an enzyme has a high affinity for its substrate. Km, or the Michaelis constant, is the substrate concentration at which the reaction rate is half of Vmax. When Km is low, it means that the enzyme can achieve half of its maximum reaction velocity at a low substrate concentration, suggesting that the enzyme binds tightly to the substrate. This tight binding often results in more efficient catalysis, as the enzyme can quickly convert the substrate into the product.

How do you determine the turnover number of an enzyme?

The turnover number, also known as kcat, is the number of substrate molecules converted into product by an enzyme molecule per unit time when the enzyme is fully saturated with substrate. It is calculated using the formula:

$k{\mathrm{cat}}_{}=\frac{V{\max }_{}}{E{t}_{}}$

Here, Vmax is the maximum reaction velocity, and Et is the total enzyme concentration. The turnover number provides insight into the catalytic efficiency of the enzyme, indicating how many reactions each enzyme molecule can catalyze per second.