Enzyme unit: Difference between revisions
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{{Short description|Unit of catalytic activity}} | {{Short description|Unit of catalytic activity}} | ||
{{distinguish|international unit{{!}}the international unit (IU) used in biological activity}} | {{distinguish|international unit{{!}}the international unit (IU) used in biological activity}} | ||
The '''enzyme unit''' | The '''enzyme unit''' or '''international unit''' (symbol '''U''' or '''IU''') is a [[Unit of measurement|unit]] measuring an [[enzyme]]'s [[Enzyme assay|catalytic activity]].<ref>{{cite journal |author=Nomenclature Committee of the International Union of Biochemistry (NC-IUB) |year=1979 |title=Units of Enzyme Activity |journal=Eur. J. Biochem. |volume=97 |issue=2 |pages=319–20 |doi=10.1111/j.1432-1033.1979.tb13116.x |doi-access=free}}</ref> An enzyme unit is defined as the amount of the enzyme that [[Catalysis|catalyzes]] the conversion of one [[Micro-|micro]][[Mole (unit)|mole]] (μmol) of [[Substrate (biochemistry)|substrate]] per minute (min) under the specified conditions of the [[Assay|assay method]].<ref>{{Cite journal |date=2018-07-01 |title=Terminology of bioanalytical methods (IUPAC Recommendations 2018) |journal=Chemistry International |volume=40 |issue=3 |pages=34 |doi=10.1515/ci-2018-0319 |hdl=10138/237212 |issn=1365-2192 |doi-access=free |hdl-access=free}}</ref> The specified conditions will usually be the [[Enzyme|optimal conditions]]—including but not limited to [[temperature]], [[pH]], and [[Substrate (biology)|substrate]] [[concentration]]—which yield the maximal substrate conversion rate for that particular enzyme. In some assay methods, one usually takes a temperature of 25°C.<ref>Principles of Biochemistry, page 94, 4th Edition, Lehninger</ref> | ||
The enzyme unit was adopted by the [[International Union of Biochemistry and Molecular Biology|International Union of Biochemistry]] in 1964. However, since the [[minute]] is not an [[SI]] base unit of time, the enzyme unit is discouraged in favor of the [[katal]] (kat), which corresponds to the amount of enzyme that catalyzes one mole of substrate per [[second]], instead. Thus 1 U = 16.67 nanokatal.<ref name="isbn_9781461585329">{{Citation |last1=Wharton |first1=Christopher W. |title=Molecular Enzymology |pages=82 |year=2013 |postscript=. |url=https://books.google.com/books?id=Y_oGCAAAQBAJ&dq=1+U+%3D+16.67+nkat&pg=PA82 |series=Tertiary Level Biology |publisher=Springer Science and Business Media |isbn=9781461585329 |last2=Eisenthal |first2=Robert}}</ref> While the katal was recommended by the 1978 [[General Conference on Weights and Measures]] and officially adopted in 1999, almost all scientific research still uses the enzyme unit, for the simple reason that enzyme assays usually last for minutes, not seconds. | |||
The enzyme unit is sometimes also called the international unit, causing confusion with the identically named [[international unit]] of biological activity. The latter is used to measure [[Biopharmaceutical|biopharmaceuticals]], like [[Vitamin|vitamins]] and [[Hormone|hormones]], and is defined by an arbitrary standard of biological activity set for each particular substance. Thus, there is no relation between the two units, despite their identical names; for example, an IU of the enzyme [[catalase]] has no meaningful relation to an IU of [[vitamin C]]. | |||
The enzyme unit | |||
==See also== | ==See also== | ||
Latest revision as of 04:32, 24 September 2025
Template:Short description Script error: No such module "Distinguish". The enzyme unit or international unit (symbol U or IU) is a unit measuring an enzyme's catalytic activity.[1] An enzyme unit is defined as the amount of the enzyme that catalyzes the conversion of one micromole (μmol) of substrate per minute (min) under the specified conditions of the assay method.[2] The specified conditions will usually be the optimal conditions—including but not limited to temperature, pH, and substrate concentration—which yield the maximal substrate conversion rate for that particular enzyme. In some assay methods, one usually takes a temperature of 25°C.[3]
The enzyme unit was adopted by the International Union of Biochemistry in 1964. However, since the minute is not an SI base unit of time, the enzyme unit is discouraged in favor of the katal (kat), which corresponds to the amount of enzyme that catalyzes one mole of substrate per second, instead. Thus 1 U = 16.67 nanokatal.[4] While the katal was recommended by the 1978 General Conference on Weights and Measures and officially adopted in 1999, almost all scientific research still uses the enzyme unit, for the simple reason that enzyme assays usually last for minutes, not seconds.
The enzyme unit is sometimes also called the international unit, causing confusion with the identically named international unit of biological activity. The latter is used to measure biopharmaceuticals, like vitamins and hormones, and is defined by an arbitrary standard of biological activity set for each particular substance. Thus, there is no relation between the two units, despite their identical names; for example, an IU of the enzyme catalase has no meaningful relation to an IU of vitamin C.
See also
References
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