Final answer:
At subsaturation substrate concentrations, the reaction rate is greater when the enzyme has higher affinity for its substrate, allowing for more efficient catalysis before reaching saturation.
Step-by-step explanation:
The reaction rate at subsaturation substrate concentrations is greater when the enzyme-substrate affinity is higher. Essentially, this means that enzymes with higher affinity for a substrate can work more efficiently even when the substrate levels are not high, because they are better at binding the available substrate molecules. In conditions where substrate concentration is low, increasing the substrate amount does not lead to a linear increase in reaction rate, resulting in a hyperbolic relationship as per the enzyme kinetics. Once the enzyme active sites are fully occupied, the reaction rate levels off even if more substrate is added, a point known as saturation. The affinity of an enzyme for its substrate is of particular importance before this saturation point is reached, as it impacts how quickly substrates can bind to the available active sites.