A fast enzyme is characterized by having a larger _____ and greater _____ _____.

The characterization of a fast enzyme centers on its efficiency in catalyzing reactions. A key feature of such enzymes is a higher Vmax. Vmax represents the maximum rate of the reaction when the enzyme is saturated with substrate. Thus, a fast enzyme can convert substrate to product more quickly, achieving a higher rate of reaction under optimal conditions.

Additionally, a greater substrate affinity can contribute to how effectively the enzyme operates; however, the term "affinity" is more precisely associated with Km (the Michaelis constant), which indicates how readily the enzyme binds to its substrate. A lower Km reflects a higher affinity, but the question specifically highlights the speed of the enzymatic reaction, which aligns primarily with Vmax in the context of enzyme kinetics.

Thus, while substrate affinity is relevant, the two key characteristics of a "fast enzyme" are embodied in the concepts of Vmax and its efficiency in processing substrates at a quicker rate.