申論題

7. (15%) Enzymes serve as catalysts in many chemical reactions in living systems. The simplest such reactions transform a single substrate into a product with the help of an enzyme, which may be represented schematically as

In this mechanism, the enzyme E is a catalyst, which only facilitates the reaction, so that its total concentration, free plus combined, [E] + [ES] = [E]o is a constant.

(b) (4%) Applying the steady-state approximation to ES, show that the initial rate V₀ at which P is formed can be described by the Michaelis-Menten equation Vo=(V_max*[S]₀)/ ([S]₀ +Km), where [S]₀ is the concentration of the substrate and V_max=k_cat [E]₀ is the maximum rate at which the product may be formed and K_m = (k_f+k_cat)/kf is the MichaelisMenten constant.