What does kcat measure in the context of enzyme kinetics?

The measure of kcat, also known as the turnover number, specifically quantifies the number of substrate molecules that a single enzyme molecule can convert into product per unit time when the enzyme is saturated with substrate. It is a key parameter in enzyme kinetics that helps assess the efficiency of an enzyme.

When the substrate concentration is much higher than the enzyme concentration, the enzyme operates at its maximum velocity (Vmax). Under these conditions, kcat can be calculated by dividing Vmax by the total enzyme concentration, leading to an understanding of how rapidly an enzyme can process substrate molecules. This is particularly useful for comparing the catalytic efficiency of different enzymes or determining how changes in enzyme structure or environmental conditions affect their activity.

In contrast, measurements related to enzyme activation energy, inhibition rates, or substrate binding affinity involve different parameters and concepts in enzyme kinetics and do not reflect the direct catalytic efficiency measured by kcat.