Use the data in the chart below to determine the answer to the...

Question

Use the data in the chart below to determine the answer to the following:

A) Rank the enzymes in order of their binding affinity to their substrate (strongest affinity → weakest affinity).

a) A → B → C.

b) C → A → B.

c) C → B → A.

d) B → A → C.

Table showing enzyme data: kcat, Km, kcat/Km, and Ki for Enzymes A, B, and C.

B) Rank the enzymes in order of their binding affinity to the inhibitor (strongest affinity → weakest affinity).

a) A → B → C.

b) B → C → A.

c) C → B → A.

d) B → A → C.

C) Which enzyme would you expect the inhibitor to affect the most? Why?

a) Enzyme A.

b) Enzyme B.

c) Enzyme C.

Accepted Answer

Alright, so here we have a 3 part practice problem broken up into part a, b, and c. And the problem says to use the data in the chart below to determine the answer to the following. And taking a look at our chart down below, notice that we're given these 3 different enzymes, enzyme a, b, and c, and then we're given the catalytic constant or the kcat or the turnover number in units of inverse seconds for each of the 3 enzymes, the Michaelis constant or the k m in units of molarity for each of the 3 enzymes, the specificity constant ratio or the kcat over the k m in units of inverse molarity inverse seconds for each of these 3 enzymes, as well as the inhibition constant of the free enzyme k I in units of molarity for each of these three enzymes. And so part a here wants us to rank the enzymes in order of their binding affinity to their substrate in terms of ranking them from their strongest affinity to substrate. And of course, we know from our previous lesson videos that when it comes to an enzyme's binding affinity to its substrate that will be indicated by the Michaelis constant k m. And of course we know that the k m has an inverse relationship with the binding affinity and so the smaller the value of the Kilometers, the stronger the binding affinity and so, we want to look for the smallest Kilometers and the smallest Kilometers is going to be enzyme c followed by enzyme b and then of course enzyme a has the greatest k m making it have the weakest affinity. And so the ranking for these enzymes will be enzyme c has the strongest, enzyme b the next, and then enzyme a has the weakest affinity. And the answer option that indicates this order is answer option c. And so we can go ahead and indicate that c here is the correct answer for part a. And so moving on to the next part, part b, it also wants us to rank the enzymes in order of their binding affinities. But this time, it's not about the binding affinity to the substrate, it's about the binding affinity to the inhibitor. And again, it wants us to rank us, rank the enzymes, in terms of their binding affinity to the inhibitor from strongest affinity to the weakest affinity. And so, of course, we know from our previous lesson videos that when it comes to an enzymes binding affinity to the inhibitor, that will be indicated by the inhibition constant Ki and the Ki we know is very very comparable to the Michaelis constant Kilometers and so it also has an inverse relationship with the binding affinity. And so the smaller the value of the k I, the stronger the binding affinity. And so the enzyme that has the smallest k I is actually enzyme a. And so, enzyme a has the smallest, the next smallest would be enzyme b, and then of course enzyme c has the greatest, k I making it have the weakest affinity. And so, the order here is going to be enzyme a, followed by b, followed by c. And that order is indicated by answer option a. So we can go ahead and highlight a here and indicate a is the correct answer for part b. And so moving on to our final part here, part c, it asks, which enzyme would you expect the inhibitor to affect the most and why? Well, when we take a look at our previous two answer options, notice that enzyme a has the weakest affinity to the substrate and it has, enzyme a has the strongest affinity to the inhibitor. And so if it has a very, very weak affinity to the substrate and a strong affinity to the inhibitor, then it's going to be inhibited the most. And so we would expect for these reasons enzyme a to be, the enzyme that is inhibited the most by this inhibitor. And, again, the reasons for this is because enzyme a has, again, the weakest affinity for its substrate yet the strongest affinity for its inhibitor. And so, this here concludes our answers to our practice problem and I'll see you guys in our next video.

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