Factors Affecting Enzyme Activity - Online Tutor, Practice Problems & Exam Prep

Factors Affecting Enzyme Activity Concept 1

Now the activity of an enzyme is the speed or rate at which an enzyme catalyzes a substrate to a product. And we're going to say the activity increases when a substrate binds to the enzyme's active site. Enzyme saturation is when there are more substrate molecules than active sites. So think of enzymes as just a finite amount. There's a given amount of enzyme and so there are only so many free and open active sites. As you add more substrates, those substrates are going to start sitting down in those active sites. Eventually, all the sites are taken up. Right? So saturation starts happening when all the sites are taken up, but there are still substrate molecules hanging around. They have nowhere to sit. So, we have reached saturation of our enzymes. All the active sites are taken up, and there's still substrate molecules waiting to get into an open active site. Right. So that's the way we're going to look at it. From here, we'll then talk about the four factors that can affect the enzyme's activity.

Factors Affecting Enzyme Activity Concept 2

For fact 1, let's take a look at the concentration of our substrate. Here we have two conditions, where we've reached enzyme saturation and where we haven't just yet. Under enzyme saturation, we have excess substrate. All the enzyme sites have been taken up; there are no available seats for our substrates to be added. But if I start adding more substrate on top of that, we have rate as our y-axis and the amount of substrate as our x-axis. This curve represents an increase in the rate as our substrates start connecting to the active sites of our enzyme. But under a saturation model, there are no open seats. So, it doesn't matter how much more substrate I add, there's no open seats, so my rate or activity is not going to increase. We reach this red line where that's just the peak. We can't go beyond that, so there is no increase in my activity.

In an unsaturated model, we have extra seats open; we don't have enough substrates. So, what do I do? I start adding more substrate. Thus, I increase the amount of substrate, and that's going to increase my activity because there are open seats. I add more substrate; they're going to go to those open seats, causing my rate to go up.

Next, we look at the concentration of our enzymes. In this one too, we also have saturated versus unsaturated. When we talk about saturated versus unsaturated, everything is just flipped. It's the exact opposite. In saturated, we have excess substrate. So what I do is I come in and I start adding more enzyme. I'm adding more seats to the room. So those substrates that are hanging out, they see more open seats, more open active sites, so they go and sit in them. This is going to increase the activity of the enzyme and therefore increase the rate, so my activity goes up. We can see that with this line; it's just going up.

Now in the unsaturated scenario, we have excess active sites. And what I do is I start adding more enzyme. I added more seats, but there's no substrates around to connect to those open seats. So there's not going to be an increase in my activity. So we would see this kind of like a straight line. The rate would not change; it would just stay flat.

Temperature is temperature dependent. Enzymes work under a good range in terms of temperature. Let's say if your temperature is below 50, the enzyme can function. But once it goes above 50, it stops working correctly. If we look at this curve, we can see that we are at 10 degrees; the rate is pretty low. But then as we start increasing it, the rate goes higher and higher because the enzyme works better at a higher temperature. But then we reach this peak right here, and that represents the maximum enzyme activity. We're going to say, once you go above 50, though, the temperature becomes too hot, and you start to denature your protein or denature your enzyme. Remember, enzymes can be protein in nature. We're going to say here most enzymes work optimally around 37 degrees Celsius. Here, if your temperature is below 50, you can have the enzyme activity increase. But then once you go above 50, you're going to denature it, so your activity is going to go down. And we can see that the peak here is around 37. It starts to tail off as we get closer and closer to 50.

For pH, we're going to say pH plus or minus 1 units of the optimal pH range. Enzymes can work under different types of pHs depending on what kind of enzyme we're dealing with. Pepsin is within our stomachs. Our stomachs are pretty acidic, so its optimal pH is 1.7. It can operate effectively between 0.7 to 2.7. Because if we subtract 1, it's 0.7. If we add 1, it's 2.7. And then amylase is within our mouth. Our mouths are close to being basic or neutral, actually closer to neutral. So 6.8 is the optimal. And then we have arginase here. This is a basic functioning enzyme. Its optimal is 9.4.

Here, we have our rate, and then we have our pH. Our max enzyme activity for most enzymes is around 7.4 or what we call physiological pH. Here we'd say that our activity of our enzyme will decrease if we go outside these optimal ranges. Now here we're going to say temperatures and pH values that lie outside optimal ranges can denature the enzyme.

So what do we mean by denature? So we're going to say denaturation is the unfolding of the 3D structure of an enzyme, which can disrupt its function. Remember, enzymes are based on their function, and that's tied to their structure here. So, if we unravel the structure, the enzyme can't work effectively.

So these are our four factors that can affect an enzyme's activity. So keep them in mind when we're talking about changing temperature, changing pH, playing around with the concentration of enzyme and substrate.

Factors Affecting Enzyme Activity Example 1

Which of the following would cause the activity of a typical enzyme to diminish, to go down? Increasing the temperature from 20 degrees to 35 degrees Celsius. This would increase my activity because the optimal temperature is 37 degrees Celsius. We're approaching closer to that optimal temperature. So this would cause it to go up. Here we say at a concentration where the substrate is 0.030 molar and the enzyme amount is 0.050, and you add more substrate. So we have more enzyme than we do substrate. So we have open seats. So if I add more substrate, they'll go to those open seats. And remember, if we're binding substrate to the active sites of enzymes, that's going to help to increase my activity. So, this would increase my activity. Adjusting the pH from 6.8 to 9.0. Most enzymes work effectively around physiological pH which is around 7.4. So, a vast majority of the enzymes would become less effective at their job because we're moving away from being closer to 7.4 or when we're at 6.8. We're moving further away from it. We're going to 9.0. That's quite basic. Most enzymes won't be able to properly function here. This would decrease the activity of my enzyme. And then finally, all statements would increase the activity of an enzyme. That's not true. We see that only option c would help to decrease the activity of an enzyme.

Pepsin, a peptidase that hydrolyzes proteins, functions in the stomach at an optimum pH of 1.5 to 2.0.

Which of the following would cause an increase in its activity?

• A. Changing the pH to 8.0. 
• B. Running the reaction at 0ºC. 
• C. Increasing the concentration of pepsin two-fold. 
• D. Changing the aqueous environment temperature to 60ºC. 

Sucrase has an optimum pH range of 4.5 – 7.0. Which of the following statements is true?

• A. Addition of HCl to increase the pH to 9.0 would decrease its activity. 
• B. Sucrase as an enzyme would catalyze the hydrolysis of fructose. 
• C. The activity of sucrase would be greater at 100ºC than at 10ºC.
• D. When [Sucrase] = 0.03 M and [Sucrose] = 0.055 M increasing [Sucrase] to 0.07 M will increase the activity.