Km is influenced by _____, but not by changes in enzyme concentration.

The correct response emphasizes that Km, or the Michaelis constant, is influenced by the presence of inhibitors. Km is a measure of the affinity of an enzyme for its substrate; it reflects the substrate concentration at which the reaction rate reaches half of its maximum velocity (Vmax). When inhibitors are present, they can alter the enzyme’s function and its interaction with the substrate.

For example, competitive inhibitors increase the Km value, indicating a decreased affinity because more substrate is needed to reach half-maximal velocity. Non-competitive inhibitors, while not affecting the Km, change the overall maximum velocity (Vmax) of the reaction. Thus, inhibitors play a direct role in influencing how substrates interact with enzymes, making them a critical factor in determining Km.

Substrate concentration influences the observed reaction rate but does not inherently alter Km itself; rather, it is a factor in determining the dynamics of the reaction at varying concentrations. Temperature and pH can affect enzyme activity and stability, which in turn can impact the overall rate of the reaction, but they do not directly change the Km. Hence, inhibitors are the primary regulatory factors concerning changes in Km.