Question

Select an enzyme that is K_m controlled, one that is k_cat controlled, and one that seems to have evolved with both in mind. Why?

Acetylcholinesterase, Carbonic Anhydrase, Catalase, Chymotrypsin, Fumarase, Urease

Answer 1

The Km constant of an enzyme helps in determining the affinity of an enzyme to a substrate. This value helps in determining how efficiently an enzyme can convert a substrate into product. The carbonic anhydrase is an example of an enzyme which is Km controlled. It is found that at the Km value of 9mM and hence it has the lowest Km value amongst all the option given. When the Km value is low, it is able to bind to the HCO3- and hence is able to convert the substrate into its product at a rapid rate.

The Kcat is the turnover number which means the number of substrate molecule which binds to the each of the active site of the enzyme and converts it into product per unit time. Hence it helps in finding out the rate of reaction when negligible amount of substrate is present. Catalase is the enzyme which is controlled by Kcat because it has a very high Kcat value and this means that the enzyme has maximum catalytic activity and hence it is able to convert huge amount of substrate into product

The acetylcholisterase is the one which is controlled by both its kcat as well as Km value and hence it helps in converting the substrate into product depending on its value and when the Km value is low, it will convert maximum product and a low Km value will reduce the conversion.