katal

Katal is the SI unit of catalytic activity. The symbol for the unit is kat. It measures the rate at which a catalyst converts substrate into product. By definition, 1 katal is the amount of catalyst that converts 1 mole of substrate per second under specified conditions, such as a defined temperature, pH, and substrate.

As a derived SI unit, the katal is dimensionally equivalent to mol s^-1. Because many biological catalysts operate at rates far below 1 mole per second, the katal is rarely used in routine reporting. More common in biochemistry are the enzyme unit (U) or the international unit (IU). One U equals 1 μmol of substrate converted per minute, which is 1×10^-6 mol per 60 seconds, or about 1.666×10^-8 mol s^-1. Consequently, 1 katal equals roughly 6×10^7 U, illustrating that the katal represents a much larger rate scale than typical enzyme activities.

The katal is defined to be useful when comparing catalytic activities under the same reaction conditions, but because catalytic rates depend strongly on factors like temperature, pH, substrate, and catalyst, researchers specify the conditions used for the measurement. While the unit formalizes catalytic rate in SI terms, in practice many enzymology studies continue to report activities in U or IU.

See also: Enzyme unit, Catalysis, SI units.