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The katal (symbol: kat) is that catalytic activity that will raise the rate of conversion by one mole per second in a specified assay system.[1] It is a unit of the International System of Units (SI)[1] used for quantifying the catalytic activity of enzymes (that is, measuring the enzymatic activity level in enzyme catalysis) and other catalysts.
| katal | |
|---|---|
| Unit system | SI |
| Unit of | catalysis |
| Symbol | kat |
| InSI base units: | mol/s |
The unit 'katal' is not attached to a specified measurement procedure or assay condition, but any given catalytic activity is: the value measured depends on experimental conditions that must be specified.[2][3] Therefore, to define the quantity of a catalyst in katals, the catalysed rate of conversion (the rate of conversion in presence of the catalyst minus the rate of spontaneous conversion) of a defined chemical reaction is measured in moles per second.[4] One katal of trypsin, for example, is that amount of trypsin which breaks one mole of peptide bonds in one second under the associated specified conditions.[clarification needed]
One katal refers to an amount of enzyme that gives a catalysed rate of conversion of one mole per second.[5][6] Because this is such a large unit for most enzymatic reactions, the nanokatal (nkat) is used in practice.[6]
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.
| Submultiples | Multiples | ||||
|---|---|---|---|---|---|
| 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 |
| 10−27 kat | rkat | rontokatal | 1027 kat | Rkat | ronnakatal |
| 10−30 kat | qkat | quectokatal | 1030 kat | Qkat | quettakatal |
The General Conference on Weights and Measures and other international organizations recommend use of the katal.[7] It replaces the non-SI enzyme unit of catalytic activity. The enzyme unit is still more commonly used than the katal,[6] especially in biochemistry.[citation needed][8] The adoption of the katal has been slow.[6][9]
The name "katal" has been used for decades. The first proposal to make it an SI unit came in 1978,[6][10] and it became an official SI unit in 1999.[6][11][12] The name comes from the Ancient Greek κατάλυσις (katalysis), meaning "dissolution";[13] the word "catalysis" itself is a Latinized form of the Greek word.[13][14]