A slower enzyme is characterized by a larger _____ value.

The statement that a slower enzyme is characterized by a larger Km value is correct because Km, or the Michaelis constant, describes the substrate concentration at which the reaction rate is half of Vmax (the maximum rate of reaction). A high Km indicates that a higher concentration of substrate is needed to achieve half-maximal velocity, which suggests a lower affinity of the enzyme for the substrate.

When an enzyme has a larger Km, it implies that it is less efficient at catalyzing the reaction at lower substrate concentrations compared to an enzyme with a smaller Km. Thus, a slower enzyme will typically exhibit a larger Km, indicating that it requires more substrate to reach a significant rate of reaction.

In contrast, Vmax represents the maximum reaction rate when the enzyme is saturated with substrate and does not inherently indicate speed in the same sense as Km. Affinity describes how tightly a substrate binds to an enzyme, and a lower affinity corresponds with a larger Km. Reaction rate refers to the speed of the enzyme activity, but it is not a direct measure like Km is. This understanding helps clarify the relationship between enzyme activity and Km, reinforcing why a larger Km correlates with slower enzymatic reactions.