Question

Carbonic anhydrase (CA) has a 25,000-fold higher activity (k_cat = 106 s^-1) than orotidine monophosphate decarboxylase (OMPD) (k_cat = 40 s-1). However, OMPD provides more than a 10¹⁰ higher “rate acceleration” than CA. Explain how this is possible.

Answer 1

Recall that k_cat is a measure of the catalytic activity of an enzyme indicating how many reactions a molecule of enzyme can catalyze per second. But Michaelis constant, K_m also plays role during rate acceleration. The k_cat/K_m ratio is useful for comparing the activities of different enzymes. It is also possible to assess the efficiency of an enzyme by measuring its catalytic proficiency. This value is equal to the rate constants for a reaction in the presence of the enzyme (k_cat/K_m) divided by the rate constant for the same reaction in the absence of the enzyme (k_n). an enzyme with rapid binding might evolve a mechanism that favored a faster reaction. An electric field around the OMPD active site enhances the rate of formation of the ES complex. Electrostatic effects allow OMPD to bind and remove OMPD much faster than expected from random collisions of enzyme and substrate.

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