Question

) Enzymes with a kcat / Km ratio of about 108 M-1 s-1 are considered to show optimal catalytic efficiency. Fumarase, which catalyzes the reversible-dehydration reaction Fumarate + H2O  Malate has a ratio of turnover number to the Michaelis-Menten constant, (kcat / Km) of 1.6 × 108 for the substrate fumarate and 3.6 × 107 for the substrate malate. Because the turnover number for both substrates is nearly identical, what factors might be involved that explain the different ratio for the two substrates?

Answer 1

Since the turnover number for both substrates is nearly identical, the Km value for malate will be greater when compared with the Km value for fumarate. Comparable turnover numbers shows there will be no significant differences in rate of conversion of substrate to product, but varying Km amount could be judged by a higher enzyme binding affinity for fumarate when compared with malate or different factors in the reaction mechanism that influence Km.