Enzyme Turnover Number Calculator (kcat)

Enzyme Turnover Number Calculator (kcat) | Online Free Tool | Elysia Tools

Tool usage guide

Learn when to use this tool, what it supports, and how real users apply it.

Key facts

Category: Education
Input types: select, number
Output type: json
Sample coverage: 4
API ready: Yes

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.

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

1Choose a calculation mode: Vmax plus enzyme amount, Vmax plus enzyme concentration, or Vmax plus protein concentration and molecular weight.
2The calculator applies kcat = Vmax ÷ [E]total using matching amount or concentration units.
3In protein mode, it converts protein concentration to enzyme concentration with [E] = 1000 × protein concentration ÷ molecular weight.
4The 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.

Examples

1. Enzyme amount route: 12 µmol/min Vmax with 0.02 µmol enzyme

Biochemistry student

Background

A saturated assay measures Vmax as 12 µmol/min and contains 0.02 µmol of active enzyme.

Problem

The student needs the turnover number in both minutes and seconds.

How to use

Select the amount mode and enter Vmax = 12 µmol/min and enzyme amount = 0.02 µmol.

{"mode":"amount","vmaxUmolMin":12,"enzymeUmol":0.02,"decimalPlaces":4}

Outcome

The calculator returns kcat ≈ 600 min⁻¹ = 10 s⁻¹, classified in the moderate range.

2. Protein route: 1 mg/mL of a 50 kDa enzyme

Laboratory researcher

Background

The enzyme stock is measured at 1 mg/mL, its molecular weight is 50 kDa, and the saturated-assay Vmax is 40 µM/min.

Problem

The researcher has protein concentration rather than enzyme molarity and needs kcat.

How to use

Select the protein mode and enter Vmax = 40 µM/min, protein concentration = 1 mg/mL, and molecular weight = 50 kDa.

FAQ

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.

{"mode":"protein","vmaxUMLMin":40,"proteinMgPerMl":1,"molecularWeightKda":50,"decimalPlaces":4}

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Learn when to use this tool, what it supports, and how real users apply it.

Key facts

Overview

When to use

How it works

Use cases

Examples

1. Enzyme amount route: 12 µmol/min Vmax with 0.02 µmol enzyme

2. Protein route: 1 mg/mL of a 50 kDa enzyme

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