The katal (symbol: kat) is the SI unit of catalytic activity. It is a derived SI unit for quantifying the catalytic activity of enzymes (measuring the enzymatic activity level in enzyme catalysis) and other catalysts. Its use is recommended by the General Conference on Weights and Measures and other international organizations. It replaces the non-SI enzyme unit. Enzyme units are, however, still more commonly used than the katal in practice at present, especially in biochemistry.
The katal is not used to express the rate of a reaction; that is expressed in units of concentration per second (or moles per liter per second). Rather, it is used to express catalytic activity which is a property of the catalyst. The katal is invariant of the measurement procedure, but the numerical quantity value is not and depends on the experimental conditions. Therefore, in order to define the quantity of a catalyst, the rate of conversion of a defined chemical reaction is specified as mols reacted per second. One katal of trypsin, for example, is that amount of trypsin which breaks a mole of peptide bonds per second under specified conditions.
|Value||SI symbol||Name||Value||SI symbol||Name|
|10−1 kat||dkat||decikatal||101 kat||dakat||decakatal|
|10−2 kat||ckat||centikatal||102 kat||hkat||hectokatal|
|10−3 kat||mkat||millikatal||103 kat||kkat||kilokatal|
|10−6 kat||µkat||microkatal||106 kat||Mkat||megakatal|
|10−9 kat||nkat||nanokatal||109 kat||Gkat||gigakatal|
|10−12 kat||pkat||picokatal||1012 kat||Tkat||terakatal|
|10−15 kat||fkat||femtokatal||1015 kat||Pkat||petakatal|
|10−18 kat||akat||attokatal||1018 kat||Ekat||exakatal|
|10−21 kat||zkat||zeptokatal||1021 kat||Zkat||zettakatal|
|10−24 kat||ykat||yoctokatal||1024 kat||Ykat||yottakatal|
The name katal has been used for decades and it became an official SI unit in 1999.
- Nomenclature Committee of the International Union of Biochemistry (NC-IUB) (1979). "Units of Enzyme Activity". Eur. J. Biochem. 97 (2): 319–20. doi:10.1111/j.1432-1033.1979.tb13116.x.
- Unit "katal" for catalytic activity (IUPAC Technical Report) Pure Appl. Chem. Vol. 73, No. 6, pp. 927–931 (2001) 
- René Dybkær (1 March 2002). "The Tortuous Road to the Adoption of katal for the Expression of Catalytic Activity by the General Conference on Weights and Measures". Clinical Chemistry. 48 (3): 586–590. PMID 11861460.
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