The graph in Figure 3-34 illustrates the change in the rate of an enzyme-catalyzed reaction as the concentration of substrate is increased.Which of the values listed below is used to calculate the enzyme turnover number? Figure 3-34

Question

The graph in Figure 3-34 illustrates the change in the rate of an enzyme-catalyzed reaction as the concentration of substrate is increased.Which of the values listed below is used to calculate the enzyme turnover number?  Figure 3-34

Quizplus · Accepted Answer

The enzyme turnover number (kcat) is defined as the maximum number of substrate molecules that can be converted to product by one enzyme molecule per unit time when the enzyme is saturated with substrate. It is calculated using the formula kcat = Vmax/[E], where [E] is the enzyme concentration. From the graph, we can see that Vmax is reached at the highest substrate concentration and that VS can be approximated as Vmax. Therefore, kcat can be calculated using the formula kcat = Vmax/[E] = VS/[E] = VS/(Et - ES), where Et is the total enzyme concentration and ES is the enzyme-substrate complex concentration at steady-state. This simplifies to kcat = VS/([E]t - [ES]). Since [ES] is negligible at high substrate concentrations, we can assume that [E]t is constant and the turnover number can be calculated as kcat = VS/[E]t, which corresponds to answer choice C.

The Graph in Figure 3-34 Illustrates the Change in the Rate