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O Antigens
The lipopolysaccharide-protein somatic antigens, usually from gram-negative bacteria, important in the serological classification of enteric bacilli. The O-specific chains determine the specificity of the O antigens of a given serotype. O antigens are the immunodominant part of the lipopolysaccharide molecule in the intact bacterial cell. (From Singleton and Sainsbury, Dictionary of Microbiology and Molecular Biology, 2d ed)
Year introduced: 1996
Catechol O-Methyltransferase Inhibitors
Compounds and drugs that inhibit or block the activity of CATECHOL O-METHYLTRANSFERASE enzymes. Drugs in this class are used in management of central nervous system disorders such as PARKINSON DISEASE.
Year introduced: 2015
Homoserine O-Succinyltransferase
The first enzyme in the METHIONINE biosynthetic pathway, this enzyme catalyzes the succinylation reaction of L-homoserine to O-succinyl-L-homoserine and COENZYME A using succinyl-CoA.
Year introduced: 2006(1980)
Serine O-Acetyltransferase
An enzyme that catalyzes the conversion of L-SERINE to COENZYME A and O-acetyl-L-serine, using ACETYL-COA as a donor.
O-Acetyl-ADP-Ribose
An acetyl ester of ADENOSINE DIPHOSPHATE RIBOSE formed during NAD-dependent deacetylation of proteins by SIRTUINS. The acetate group resides on the ribose ring where nicotinamide was cleaved from NAD during the reaction. Several isomers of O-acetyl-ADP-ribose have been isolated from the reaction.
Year introduced: 2003
O(6)-Methylguanine-DNA Methyltransferase
An enzyme that transfers methyl groups from O(6)-methylguanine, and other methylated moieties of DNA, to a cysteine residue in itself, thus repairing alkylated DNA in a single-step reaction. EC 2.1.1.63.
Year introduced: 1998
3-O-Methylglucose
A non-metabolizable glucose analogue that is not phosphorylated by hexokinase. 3-O-Methylglucose is used as a marker to assess glucose transport by evaluating its uptake within various cells and organ systems. (J Neurochem 1993;60(4):1498-504)
Year introduced: 1997
Carnitine O-Acetyltransferase
An enzyme that catalyzes the formation of O-acetylcarnitine from acetyl-CoA plus carnitine. EC 2.3.1.7.
Year introduced: 1998(1975)
Sterol O-Acyltransferase 2
A sterol O-acyltransferase that catalyzes reaction of Acyl-CoA and cholesterol into CoA and cholesterol ester. It is a distinct enzyme from Acetyl-CoA C-Acetyltransferase 2, which is also referred to as ACAT2.
Year introduced: 2024 (2001)
Retinol O-Fatty-Acyltransferase
An enzyme that catalyzes the acyl group transfer of acyl COENZYME A to RETINOL to generate COENZYME A and a retinyl ester.
Year introduced: 2006(1977)
1-Acylglycerol-3-Phosphate O-Acyltransferase
An enzyme that catalyzes the acyl group transfer of ACYL COA to 1-acyl-sn-glycerol 3-phosphate to generate 1,2-diacyl-sn-glycerol 3-phosphate. This enzyme has alpha, beta, gamma, delta and epsilon subunits.
Diacylglycerol O-Acyltransferase
An enzyme that catalyses the last step of the TRIACYLGLYCEROL synthesis reaction in which diacylglycerol is covalently joined to LONG-CHAIN ACYL COA to form triglyceride. It was formerly categorized as EC 2.3.1.124.
Guanosine 5'-O-(3-Thiotriphosphate)
Guanosine 5'-(trihydrogen diphosphate), monoanhydride with phosphorothioic acid. A stable GTP analog which enjoys a variety of physiological actions such as stimulation of guanine nucleotide-binding proteins, phosphoinositide hydrolysis, cyclic AMP accumulation, and activation of specific proto-oncogenes.
Year introduced: 1991
7-Alkoxycoumarin O-Dealkylase
A drug-metabolizing enzyme found in the hepatic, placental and intestinal microsomes that metabolizes 7-alkoxycoumarin to 7-hydroxycoumarin. The enzyme is cytochrome P-450- dependent.
Year introduced: 1990
Chloramphenicol O-Acetyltransferase
An enzyme that catalyzes the acetylation of chloramphenicol to yield chloramphenicol 3-acetate. Since chloramphenicol 3-acetate does not bind to bacterial ribosomes and is not an inhibitor of peptidyltransferase, the enzyme is responsible for the naturally occurring chloramphenicol resistance in bacteria. The enzyme, for which variants are known, is found in both gram-negative and gram-positive bacteria. EC 2.3.1.28.
Year introduced: 1998(1989)
Protein O-Methyltransferase
An enzyme that catalyzes the transfer of methyl groups from S-adenosylmethionine to free carboxyl groups of a protein molecule forming methyl esters. EC 2.1.1.-.
Year introduced: 1991(1977)
CDPdiacylglycerol-Serine O-Phosphatidyltransferase
An enzyme that catalyzes the formation of phosphatidylserine and CMP from CDPdiglyceride plus serine. EC 2.7.8.8.
Oxidoreductases, O-Demethylating
Drug metabolizing enzymes which oxidize methyl ethers. Usually found in liver microsomes.
Year introduced: 1991(1975)
o-Phthalaldehyde
A reagent that forms fluorescent conjugation products with primary amines. It is used for the detection of many biogenic amines, peptides, and proteins in nanogram quantities in body fluids.
o-Chlorobenzylidenemalonitrile
A riot control agent which causes temporary irritation of the eyes and the mucosal surface of the respiratory tract. It is a more potent irritant than OMEGA-CHLOROACETOPHENONE, but less incapacitating.