What is the definition of Km, the Michaelis constant?

The correct choice, which defines Km, the Michaelis constant, is that it represents the concentration of substrate at which the enzyme is operating at half its maximal velocity. Km is a crucial parameter in enzyme kinetics because it provides insight into the enzyme's affinity for its substrate. A lower Km value indicates a higher affinity, meaning that the enzyme reaches half of its maximum velocity at a lower substrate concentration. Conversely, a higher Km suggests a lower affinity.

Understanding Km in this context allows researchers and biochemists to infer how efficiently an enzyme can catalyze a reaction under specific substrate concentrations. This characteristic is especially important in evaluating enzyme behavior in metabolic processes and in designing inhibitors or drugs that target specific enzymes.

The other concepts mentioned, such as enzyme saturation and maximum velocity, are related but do not define Km. The concentration of substrate at which the enzyme is completely saturated refers to a different metric related to Vmax, the maximum velocity, which is when all active sites of the enzyme are occupied. The maximum velocity itself does not indicate a concentration but rather the rate of reaction when the enzyme is fully engaged with the substrate. Furthermore, the rate constant for the conversion of the enzyme-substrate complex to product is more associated with reaction kinetics rather than the definition of