AAMC FL Practice Exam

What term describes enzymes that exhibit a Hill coefficient greater than 1?

1. Inhibition

2. Cooperativity

3. Allostericity

4. Specificity

The correct answer is: Cooperativity

Enzymes that exhibit a Hill coefficient greater than 1 are described as demonstrating cooperativity. This term reflects the behavior of enzymes that show an increased likelihood of undergoing a conformational change and thus increasing their activity as more substrates bind to them. In cooperative enzymes, the binding of a substrate to one active site increases the affinity of other active sites for the substrate, which can result in a more efficient catalytic process. This cooperative behavior can often be observed in multi-subunit enzymes, where the interaction among different subunits leads to a more complex response to substrate concentration. Hence, a Hill coefficient greater than 1 indicates positive cooperativity, meaning that the enzyme's activity is enhanced as more substrate molecules are present, which typically is characteristic of sigmoidal (S-shaped) enzyme kinetics instead of the hyperbolic kinetics often seen with non-cooperative enzymes. Other terms, such as inhibition, allostericity, and specificity, relate to different mechanisms or characteristics of enzyme behavior but do not specifically focus on the cooperative increase in activity associated with a Hill coefficient greater than 1. Inhibition refers to a decrease in enzyme activity, allostericity generally encompasses both activation and inhibition through different conformational changes, and specificity describes the ability of an enzyme to select