AAMC FL Practice Exam

What can be inferred from a high Kcat value for an enzyme?

1. The enzyme has a low affinity for its substrate

2. The enzyme is highly efficient and has a rapid turnover

3. The enzyme is unavailable at higher substrate concentrations

4. The enzyme's activity is inhibited by excess substrate

The correct answer is: The enzyme is highly efficient and has a rapid turnover

A high Kcat value for an enzyme indicates that the enzyme has a rapid turnover rate, meaning it can convert substrate molecules to product quickly per unit of time when fully saturated with substrate. Kcat, known as the turnover number, defines how many substrate molecules one enzyme molecule converts to product in a given time interval at saturating substrate concentrations. This high turnover suggests that the enzyme is highly efficient, allowing it to catalyze reactions swiftly, which is particularly beneficial in biological systems where reaction speed can be crucial for maintaining metabolic processes. Thus, the inference that the enzyme is highly efficient and exhibits rapid turnover aligns precisely with what a high Kcat value represents. Other choices may introduce misconceptions: a low affinity for the substrate is related to the Michaelis constant (Km), not Kcat; suggesting the enzyme is unavailable at higher concentrations misinterprets enzyme saturation; and the notion that the enzyme is inhibited by excess substrate does not follow from observing Kcat alone. Therefore, the high Kcat value is a clear indicator of effective enzymatic function.