AAMC FL Practice Exam

What is indicated by a low Km value in enzyme kinetics?

1. A high enzyme efficiency and strong substrate binding

2. A low level of enzyme activity

3. A weak binding affinity for the substrate

4. A slow reaction rate

The correct answer is: A high enzyme efficiency and strong substrate binding

A low Km value in enzyme kinetics indicates a high affinity between the enzyme and its substrate, meaning that the enzyme can effectively bind to the substrate even at low concentrations. This strong substrate binding leads to increased enzyme efficiency, as it facilitates the formation of the enzyme-substrate complex more readily. When Km is low, it reflects that the rate of reaction reaches half its maximum velocity (Vmax) at a lower concentration of substrate, which showcases how tightly the enzyme holds onto the substrate. This characteristic can be particularly advantageous in metabolic pathways where enzymes need to respond quickly to changes in substrate concentration, ensuring that reactions can proceed efficiently even when substrate levels are not high. In contrast, other options relate to different aspects of enzymatic behavior: a high Km would suggest weak substrate binding, while a low level of enzyme activity or a slow reaction rate are not directly indicated by Km values; these are instead influenced by other factors such as enzyme concentration, conditions, and the presence of inhibitors.