The Michaelis constant, K_m, is often spoken of as if it were a measure of the affinity of the enzyme for the substrate: the lower the K_m, the higher the binding affinity. This would be true if K_m were the same as K_d (the equilibrium constant for the dissociation reaction), but it is not. For an enzyme-catalyzed reaction

A. In terms of these rate constants, what is K_d for dissociation of the ES complex to E + S?

B. Under what conditions is K_m approximately equal to K_d?

C. Does K_m consistently overestimate or underestimate the binding affinity? Or does it sometimes overestimate and sometimes underestimate the binding affinity?