Not to be confused with the international unit (IU) used in biological activity.
The enzyme unit, or international unit for enzyme (symbol U, sometimes also IU) is a unit of enzyme's catalytic activity.[1]
1 U (μmol/min) is defined as the amount of the enzyme that catalyzes the conversion of one micromole of substrate per minute under the specified conditions of the assay method.[2]
The specified conditions will usually be the optimum conditions, including but not limited to temperature, pH, and substrate concentration, that yield the maximal substrate conversion rate for that particular enzyme. In some assay method, one usually takes a temperature of 25°C.[3]
The enzyme unit was adopted by the International Union of Biochemistry in 1964. Since the minute is not an SI base unit of time, the enzyme unit is discouraged in favor of the katal, the unit recommended by the General Conference on Weights and Measures in 1978 and officially adopted in 1999.
One katal is the enzyme activity that converts one mole of substrate per second under specified assay conditions, so
1 U = 1 μmol/min = 1/60 μmol/s ≈ 16.67 nmol/s;
16.67 nkat = 16.67 nmol/s;
Therefore, 1 U = 16.67 nkat[4]
While the katal may be recommended, almost all scientific research today still uses the system based on the minute, for the simple reason that enzyme assays are measured in minutes, not seconds.
The concept of enzyme unit should not be confused with the one of international unit (IU). Although it is true that 1 U = 1 IU[5] (because, for many enzymes, the existing U was adopted as the later IU), international units can be defined for the biologic activity of many other kinds of substance besides enzymes (for example, vitamins and hormones).
^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.
^Principles of Biochemistry, page 94, 4th Edition, Lehninger
^Wharton, Christopher W.; Eisenthal, Robert (2013), Molecular Enzymology, Tertiary Level Biology, Springer Science and Business Media, p. 82, ISBN 9781461585329.
^Bommarius, Andreas S.; Riebel-Bommarius, Bettina R. (2007), Biocatalysis: Fundamentals and Applications, John Wiley and Sons, p. 30, ISBN 9783527606054.
The enzymeunit, or international unit for enzyme (symbol U, sometimes also IU) is a unit of enzyme's catalytic activity. 1 U (μmol/min) is defined as...
concentration of an enzyme can be expressed in molar amounts, as with any other chemical, or in terms of activity in enzymeunits. Enzyme activity is a measure...
Enzyme unit, a measurement of active enzyme in a sample International unit, a unit of measurement for nutrients and drugs Unit number, the number 1 Unit, identity...
Enzymes (/ˈɛnzaɪmz/) are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called...
specified assay system. It is a unit of the International System of Units (SI) used for quantifying the catalytic activity of enzymes (that is, measuring the...
biocatalysis through isolated enzymes is considered more economical than use of whole cells. Enzymes may be used as a unit operation within a process to...
of a system. 'u' is the symbol for the atomic mass unit and 'U' is the symbol for one enzymeunit. In the International Phonetic Alphabet, the close back...
time unit. The biochemical equivalent is the enzymeunit. For more information on the efficiency of enzymatic catalysis, see the article on enzymes. In...
An artificial enzyme is a synthetic organic molecule or ion that recreates one or more functions of an enzyme. It seeks to deliver catalysis at rates...
can be a peptide unit, or can be independently-folding domains comprising more than 100 residues. Although they limit the enzyme's ability, these N-terminal...
enzyme, also known as brancher enzyme or glycogen-branching enzyme is an enzyme that in humans is encoded by the GBE1 gene. Glycogen branching enzyme...
active site will execute for a given enzyme concentration [ET] for enzymes with two or more active sites. For enzymes with a single active site, kcat is...
4; systematic name 4-β-D-glucan 4-glucanohydrolase) is any of several enzymes produced chiefly by fungi, bacteria, and protozoans that catalyze cellulolysis...
repeating disaccharide units of →4)GlcAβ(1→3)GlcNAcβ(1→ and has a very high molecular mass, ranging from 105 to 107 Da. Each HAS enzyme is capable of transglycosylation...
A protease (also called a peptidase, proteinase, or proteolytic enzyme) is an enzyme that catalyzes proteolysis, breaking down proteins into smaller polypeptides...
of bilirubin reduction. It is formed in the intestines by the bacterial enzyme bilirubin reductase. About half of the urobilinogen formed is reabsorbed...
Deubiquitinating enzymes (DUBs), also known as deubiquitinating peptidases, deubiquitinating isopeptidases, deubiquitinases, ubiquitin proteases, ubiquitin...
many animal cells. They are spherical vesicles that contain hydrolytic enzymes that digest many kinds of biomolecules. A lysosome has a specific composition...
different functions in cells, such as storage and transport of proteins, enzymes and signal transduction proteins, or infectious diseases. The abundance...
subunit, regulation is accomplished by factors outside the protein. An enzyme composed of both regulatory and catalytic subunits when assembled is often...
compatible with self-organization on a metal sulfide surface. Its key enzymeunit, carbon monoxide dehydrogenase/acetyl-CoA synthase, contains mixed nickel-iron-sulfur...
Lisinopril is a medication belonging to the drug class of angiotensin-converting enzyme (ACE) inhibitors and is used to treat hypertension (high blood pressure)...
without the enzyme, 18 milliseconds with the enzyme). The molecules bound and acted upon by enzymes are called substrates. Although enzymes can consist...
one most commonly used. Modrich-Lehman unit - this is rarely used, and one unit is defined as the amount of enzyme required to convert 100 nmoles of d(A-T)n...
(GGPP). In both MVA and MEP pathways, IPP is isomerized to DMAPP by the enzyme isopentenyl pyrophosphate isomerase. IPP and DMAPP condense to give geranyl...
stored as glycogen in the liver and muscles, the enzyme UDP-glucose pyrophosphorylase forms a UDP-glucose unit by combining glucose 1-phosphate with uridine...