What is the term for a more precise measure of enzyme efficiency, considering both kcat and Km?

The term that represents a more precise measure of enzyme efficiency, considering both the turnover number (kcat) and the Michaelis constant (Km), is indeed the ratio of kcat to Km. This ratio provides a comprehensive insight into how effectively an enzyme converts substrate into product under specific conditions.

kcat, known as the turnover number, indicates the maximum number of substrate molecules converted to product by an enzyme molecule in a given time when the enzyme is fully saturated with substrate. On the other hand, Km reflects the substrate concentration at which the reaction rate is half of its maximum value, giving insight into the enzyme's affinity for the substrate.

The kcat/Km ratio combines these two important parameters into a single value that allows for the comparison of enzyme efficiency across different enzymes or conditions. A higher ratio indicates a more efficient enzyme, as it suggests that the enzyme can process substrates quickly even at lower concentrations. Thus, the kcat/Km ratio serves as an important metric in enzymology for assessing how well an enzyme performs under physiological conditions.