# Question: the following problem asks students to think about enzyme kinetics...

###### Question details

The following problem asks students to think about enzyme kinetics in the framework of the Michaelis-Menton equation. It asks students to consider experiments to determine values for Km and Vmax and to draw graphs showing that they understand the concepts of Km and Vmax. It also requires students to understand what the units involved in such experiments are and what they mean (necessary to put correct units on the graph axes).

1. Carbonic anhydrase is an enzyme that will convert CO2 and water into HCO3.

CO2 + H20 > H+ + HCO3

Important: Assume the Km of one variant of carbonic anhydrase is 1 µM.

First, imagine an experiment employing 10 test tubes. The test tubes are all filled with 100 ml water. Imagine that the different test tubes have different concentrations of CO2, ranging from 0.1 µM to 10 mM CO2. Initially, there is NO enzyme in any of the test tubes.

(a) Draw a graph showing what you might expect to see for the amount of HCO3 in each of the test tubes 1 minute after the addition of CO2. Be sure to label the axes of the graph. Designate this curve as “A” (note: the exact values on the Y axes here are guestimates – you get to make them up).

(b) Now, imagine that the test tubes are filled with water and a significant amount of the enzyme carbonic anhydrase in each test tube. Assume that the enzyme has a Km of 0.5 uM. Draw on the same graph as before what you might expect to see for the amount of HCO3 in each of the test tubes 1 minute after the addition of CO2. Label this curve “B”. (note: again, the exact values on the Y axes here are guestimates – you get to make them up).obtained in the first condition (without enzyme) from the data obtained in the experiments obtained when the enzyme is present. Label this curve “C”.

(d). Using the data from C above (that is, subtracting the background production of CO2 due to simple mass action from that resulting from the combination of enzyme action and mass action), draw a separate graph showing the alteration in the rate of carbonic anhydrase as the CO2 level is varied as a percentage of the maximal rate of HCO3 production – that is, 100% is as fast as the enzyme can function. Be sure to label the axes of the graphs. That is, again draw a graph showing what you might expect to see for the amount of HCO3 produced by the action of of the enzyme in each of the test tubes 1 minute after the addition of CO2.