Michaelis & Menten assumed that the initial reaction for an enzyme catalyzed reaction could be written as shown:

Using this, the rate/velocity of ES-complex breakdown can be expressed by:

• A. k₁ ([E]_T – [ES]).
• B. k₁ ([E]_T – [ES])[S].
• C. k₂ [ES].
• D. k_-1 [ES] + k₂ [ES].

Answer: (D)

Verified step by step guidance

1. Understand the Michaelis-Menten model: It describes the rate of enzymatic reactions by relating reaction rate to substrate concentration. The model assumes the formation of an enzyme-substrate complex (ES) as an intermediate step.
2. Identify the reaction steps: The enzyme (E) binds to the substrate (S) to form the enzyme-substrate complex (ES). This complex can either dissociate back to E and S or proceed to form the product (P) and release the enzyme.
3. Write the rate equations: The formation of ES is governed by the rate constant k1, and its breakdown is governed by k-1 (dissociation back to E and S) and k2 (formation of product P).
4. Express the breakdown of ES: The breakdown of the ES complex can be expressed as the sum of the rates of its dissociation and conversion to product, which is given by the equation: v = k-1 [ES] + k2 [ES].
5. Interpret the equation: The term k-1 [ES] represents the rate of ES dissociating back to E and S, while k2 [ES] represents the rate of ES converting to product P. Together, they describe the total rate of ES breakdown.