# Enzyme Turnover Number Calculator (kcat) kcat = Vmax ÷ [E]total in min⁻¹ and s⁻¹, entered as enzyme amount, enzyme concentration, or protein concentration + molecular weight; bands results from very slow to catalase-class. Educational use only. > Canonical page: https://elysiatools.com/en/tools/enzyme-turnover-number - **Category:** Education - **Keywords:** turnover number calculator, kcat calculator, vmax over enzyme concentration, catalytic rate constant, enzyme turnover frequency, active site concentration, protein molecular weight to molarity, michaelis menten kinetics, enzyme kinetics calculator, biochemistry calculator, lab calculator ## Overview Calculate an enzyme’s turnover number, kcat, from Vmax and total enzyme or active-site concentration. Enter enzyme amount, enzyme concentration, or protein concentration with molecular weight to obtain kcat in min⁻¹ and s⁻¹. This calculator is intended for educational use and experiment planning. ## Inputs - **Calculation Mode** (select): How you know the enzyme: as an amount, a concentration, or protein concentration plus molecular weight. - **Vmax (µmol/min)** (number): Maximal velocity from a saturated assay (amount mode). - **Enzyme Amount (µmol)** (number): Total enzyme (better: active-site) amount in the assay (amount mode). - **Vmax (µM/min)** (number): Maximal velocity as a concentration rate (concentration and protein modes). - **Enzyme Concentration (µM)** (number): Enzyme (active-site) concentration (concentration mode). - **Protein Concentration (mg/mL)** (number): Protein concentration of the enzyme stock (protein mode). - **Molecular Weight (kDa)** (number): Molecular weight of one active-site-bearing subunit (protein mode). - **Decimal Places** (number) ## When to use - You have Vmax and the enzyme amount in a saturated assay. - You know Vmax and the enzyme or active-site concentration in µM. - You have protein concentration in mg/mL and molecular weight in kDa and need to estimate enzyme molarity. ## How it works - Choose a calculation mode: Vmax plus enzyme amount, Vmax plus enzyme concentration, or Vmax plus protein concentration and molecular weight. - The calculator applies kcat = Vmax ÷ \[E\]total using matching amount or concentration units. - In protein mode, it converts protein concentration to enzyme concentration with \[E\] = 1000 × protein concentration ÷ molecular weight. - The result is reported in min⁻¹ and s⁻¹, with displayed precision controlled by the decimal-places setting. ## Use cases - Compare catalytic turnover rates across enzyme preparations or assay conditions. - Convert protein assay data and molecular weight into an enzyme concentration for kcat estimation. - Check enzyme-kinetics calculations when interpreting saturated-assay Vmax measurements. ## Frequently asked questions ### What is kcat? kcat is the enzyme turnover number: the number of substrate molecules converted per active site per second under the measured conditions. ### What inputs does the calculator accept? It accepts Vmax with enzyme amount, Vmax with enzyme concentration, or Vmax with protein concentration and molecular weight. ### What units are used for the result? The calculator reports kcat in min⁻¹ and s⁻¹. ### Should enzyme concentration represent active sites? Yes. Use the total concentration of active sites when the enzyme has multiple active-site-bearing subunits. ### Is this calculator suitable for clinical or production decisions? No. It is intended for education and experiment planning, not as a substitute for validated laboratory analysis. ## Related tools - [PCR Annealing Temperature Calculator (Ta = Tm − 5°C)](https://elysiatools.com/en/tools/annealing-temperature-calculator): PCR Ta by the simple rule (lower primer Tm − 5°C) or the Rychlik 1990 formula (0.3·Tm_primer + 0.7·Tm_product − 14.9), with a ±3°C gradient window and primer-Tm mismatch warning. Derived from Rychlik 1990, Innis & Gelfand 1990, Lorenz 2012. 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