AAMC FL Practice Exam

In the context of Michaelis-Menten kinetics, what is represented by Km?

1. The maximum amount of substrate an enzyme can process

2. The substrate concentration at half the maximum velocity

3. The total turnover rate of enzyme activity

4. The binding affinity of the enzyme to the substrate

The correct answer is: The substrate concentration at half the maximum velocity

In Michaelis-Menten kinetics, Km represents the substrate concentration at which the reaction velocity is half of the maximum velocity (Vmax). This value is crucial because it provides insight into how efficiently an enzyme converts a substrate into product. A low Km indicates a high affinity between the enzyme and the substrate, meaning that even at low substrate concentrations, the enzyme can achieve significant rates of reaction. Conversely, a high Km suggests a lower affinity, requiring a higher concentration of substrate to reach half of the maximum reaction velocity. Understanding Km helps in comparing the efficiency of different enzymes and can also indicate how changes in conditions affect enzyme kinetics. It is important to note that while Km reflects enzyme-substrate interactions and can be used to infer binding affinity, it is specifically defined as the substrate concentration at which the enzyme operates at half its maximum velocity.