|Unit system||SI derived unit|
|In SI base units:||mol/s|
The katal (symbol: kat) is the unit of catalytic activity in the International System of Units (SI). It is a derived SI unit for quantifying the catalytic activity of enzymes (that is, measuring the enzymatic activity level in enzyme catalysis) and other catalysts.
The katal is invariant of the measurement procedure, but the measured numerical value is not; the value depends on the experimental conditions. Therefore, to define the quantity of a catalyst in katals, the rate of conversion of a defined chemical reaction is specified as moles reacted per second. One katal of trypsin, for example, is that amount of trypsin which breaks one mole of peptide bonds in one second under specified conditions.[clarification needed]
One katal refers to an enzyme catalysing the reaction of one mole of substrate per second. Because this is such a large unit for most enzymatic reactions, the nanokatal (nkat) is used in practice.
The katal is not used to express the rate of a reaction; that is expressed in units of concentration per second, as moles per liter per second. Rather, the katal is used to express catalytic activity, which is a property of the catalyst.
|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 General Conference on Weights and Measures and other international organizations recommend use of the katal. It replaces the non-SI enzyme unit of catalytic activity. The enzyme unit is still more commonly used than the katal, especially in biochemistry. The adoption of the katal has been slow.
The name "katal" has been used for decades. The first proposal to make it an SI unit came in 1978, and it became an official SI unit in 1999. The name comes from the Ancient Greek κατάλυσις (katalysis), meaning "dissolution"; the word "catalysis" itself is a Latinized form of the Greek word.