Kcat is a fundamental kinetic parameter in enzyme kinetics that describes the catalytic efficiency of an enzyme. It is also known as the turnover number because it represents the number of substrate molecules that one enzyme can catalyze per unit time. Kcat is a first-order rate constant with the unit of s-1. It determines the reaction rate when the enzyme is fully occupied at a saturating concentration of the substrate. Kcat is calculated by dividing the maximum reaction rate (Vmax) by the total enzyme concentration. The units of Kcat are time−1, for example, 35/second means that each molecule of enzyme is catalyzing the formation of 35 molecules of product every second. Kcat is a constant for an enzyme under given conditions.