What effect does an allosteric modifier have on an enzyme's Km based on enzyme kinetic principles?

• A. Completely inhibits enzyme activity
• B. Decreases Km
• C. Increases Km
• D. Has no effect on enzyme activity

Answer: (C)

An allosteric modifier influences an enzyme's activity by binding to a site other than the active site, which can result in conformational changes to the enzyme. This interaction can lead to an increase in the enzyme's Km, which is the Michaelis constant reflecting the affinity of the enzyme for its substrate. When an allosteric inhibitor binds to the enzyme, it typically stabilizes a conformation of the enzyme that has a lower affinity for the substrate. As a result, a higher concentration of substrate will be required to achieve half-maximal velocity, thus increasing the Km value.

In contrast, an allosteric activator usually decreases the Km, enhancing substrate affinity. Therefore, if the modifier is an inhibitor, it results in an increased Km, which is indicative of a decreased affinity for the substrate. This principle is crucial for understanding enzyme regulation and the effects of various modifiers on enzymatic functions in biological systems.