The katal (symbol: kat) is the unit of catalytic activity in 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.

Unit systemSI
Unit ofcatalysis
In SI base units:mol/s

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.[2] 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.[3][4] Because this is such a large unit for most enzymatic reactions, the nanokatal (nkat) is used in practice.[4]


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.

SI multiplesEdit

SI multiples of katal (kat)
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.[5] It replaces the non-SI enzyme unit of catalytic activity. The enzyme unit is still more commonly used than the katal,[4] especially in biochemistry.[citation needed] The adoption of the katal has been slow.[4][6]


The name "katal" has been used for decades. The first proposal to make it an SI unit came in 1978,[4][7] and it became an official SI unit in 1999.[4][8][9] The name comes from the Ancient Greek κατάλυσις (katalysis), meaning "dissolution";[10] the word "catalysis" itself is a Latinized form of the Greek word.[10][11]


  1. ^ Nomenclature Committee of the International Union of Biochemistry (NC-IUB) (1979). "Units of Enzyme Activity". European Journal of Biochemistry. 97 (2): 319–20. doi:10.1111/j.1432-1033.1979.tb13116.x. Archived from the original on 4 May 2022.
  2. ^ Dybkær, René (2001). "UNIT "KATAL" FOR CATALYTIC ACTIVITY (IUPAC Technical Report)" (PDF). Pure and Applied Chemistry. 73 (6): 927–931. doi:10.1351/pac200173060927. S2CID 195819612.
  3. ^ Tipton, Keith F.; Armstrong, Richard N.; Bakker, Barbara M.; Bairoch, Amos; Cornish-Bowden, Athel; Halling, Peter J.; Hofmeyr, Jan-Hendrik; Leyh, Thomas S.; Kettner, Carsten; Raushel, Frank M.; Rohwer, Johann; Schomburg, Dietmar; Steinbeck, Christoph (2014-05-01). "Standards for Reporting Enzyme Data: The STRENDA Consortium: What it aims to do and why it should be helpful". Perspectives in Science. 1 (1–6): 131–137. doi:10.1016/j.pisc.2014.02.012. ISSN 2213-0209.
  4. ^ a b c d e f Baltierra-Trejo, Eduardo; Márquez-Benavides, Liliana; Sánchez-Yáñez, Juan Manuel (2015-12-01). "Inconsistencies and ambiguities in calculating enzyme activity: The case of laccase". Journal of Microbiological Methods. 119: 126–131. doi:10.1016/j.mimet.2015.10.007. ISSN 0167-7012. PMID 26459230.
  5. ^ "SI Brochure, Table 3: Coherent derived units in the SI with special names and symbols)". Bureau international des poids et mesures (BIPM). Retrieved 2019-05-13.
  6. ^ Dybkaer, René (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. doi:10.1093/clinchem/48.3.586. ISSN 0009-9147. PMID 11861460.
  7. ^ "Units of Enzyme Activity Recommendations 1978". European Journal of Biochemistry. Nomenclature Committee of the International Union of Biochemistry (NC-IUB). 97 (2): 319–320. 1979. doi:10.1111/j.1432-1033.1979.tb13116.x.
  8. ^ Dybkær, René (2001). "UNIT "KATAL" FOR CATALYTIC ACTIVITY (IUPAC Technical Report)" (PDF). Pure and Applied Chemistry. 73 (6): 927–931. doi:10.1351/pac200173060927. S2CID 195819612.
  9. ^ "Topic 20: Working with enzymes" (PDF). The Association for Science Education. 2016. Retrieved 31 October 2020.
  10. ^ a b Houghton Mifflin Harcourt, The American Heritage Dictionary of the English Language, Houghton Mifflin Harcourt
  11. ^ Harper, Douglas. "catalysis (n.)". Etymonline. Retrieved 2019-04-03.

External linksEdit