Turnover Number (kcat) Calculator

kcat is the turnover number that represents the maximum number of substrate molecules converted to product per enzyme molecule per second when the enzyme is saturated with substrate. It's a measure of the catalytic efficiency of an enzyme.

kcat is typically expressed in reciprocal seconds (s⁻¹), which represents the number of catalytic cycles per second that each enzyme molecule can perform at maximum velocity.

kcat is calculated using the formula: kcat = Vmax / [E]t, where Vmax is the maximum reaction velocity and [E]t is the total enzyme concentration. The calculator converts Vmax from µmol/min to µmol/s for proper units.

No, kcat cannot exceed the diffusion limit, which is approximately 10⁸ to 10⁹ M⁻¹s⁻¹. Enzymes that approach this limit are considered catalytically perfect and are limited only by how fast substrate can reach the active site.

kcat measures the maximum turnover rate of the enzyme (catalytic efficiency), while Km (Michaelis constant) measures the substrate concentration at which the reaction velocity is half of Vmax. Together, kcat/Km represents the catalytic efficiency.

A high kcat value indicates that the enzyme is highly efficient at converting substrate to product, meaning it can process more substrate molecules per unit time. This suggests better catalytic performance.

The conversion is necessary to ensure proper units for kcat calculation. Since kcat is expressed in s⁻¹, Vmax must be in units per second rather than per minute for the calculation to be dimensionally correct.

The turnover number can be affected by temperature, pH, ionic strength, presence of inhibitors or activators, enzyme purity, and structural modifications to the enzyme. Optimal conditions typically yield the highest kcat values.