Turnover number

Turnover number (also known as kcat) is a concept in enzyme kinetics. It represents the maximum number of chemical conversions of substrate molecules per second that a single catalytic site will execute for a given enzyme concentration enzyme concentration under saturating conditions of the substrate.

Definition

The turnover number is defined as the number of molecules of substrate that an enzyme can convert into product per enzyme molecule per second. It is a measure of the catalytic activity of the enzyme, and is often used to compare the efficiencies of different enzymes, or different substrates of the same enzyme.

Calculation

The turnover number is calculated by dividing the maximum rate of reaction (Vmax) by the concentration of the enzyme ([E]). This gives the units of the turnover number as s^-1, which means "per second".

Factors affecting turnover number

The turnover number of an enzyme can be affected by a number of factors, including the concentration of the substrate, the temperature and pH of the reaction, and the presence of any inhibitors or activators.

See also

• Michaelis-Menten kinetics
• Enzyme kinetics
• Catalysis
• Enzyme inhibitor
• Enzyme activator