Enzyme Kinetics: ConcepTest and Example Problem

Try to answer this ConcepTest and solve the example problem before using this module. Studies show that trying to answer the questions before studying material improves learning and retention. We suggest that you write down the reasons for your answers. By the end of this module, you should be able to answer these on your own. Answers will be given at the end of this module.

image of a concepTest for the Enzyme kinetics module on LearnChemE.com
Example Problem 1

Consider the following proposed mechanism for the reaction of two separate reactant molecules (substrates S1 and S2) to produce a product P catalyzed by an enzyme E.

E + S1 → ES1         (1)

ES1 → E + S1         (2)

ES1 + S2 → P + E  (3)

Derive the rate expression for product formation (assuming that the steady-state approximation applies) in terms of the rate constant for each step, the concentrations of substrate species, and the total concentration of enzyme. According to this mechanism, will the reaction rate ever be less than first order in S2? Briefly explain.