enzyme (en´zIm)

A protein that acts as a catalyst to induce chemical changes in other substances, itself remaining apparently unchanged by the process. E.'s, with the exception of those discovered long ago (e.g., pepsin, emulsin), are generally named by adding -ase to the name of the substrate on which the e. acts (e.g., glucosidase), the substance activated (e.g., hydrogenase), and/or the type of reaction (e.g., oxidoreductase, transferase, hydrolase, lyase, isomerase, ligase or synthetase-these being the six main groups in the Enzyme Nomenclature Recommendations of the International Union of Biochemistry). For individual enzymes not listed below, see the specific name.organic catalyst (1); [G. + L. en,, in, + zyme, leaven]
acetyl-activating e. acetyl-CoA ligase
acyl-activating e. 1. long-chain fatty acid-CoA ligase 2. butyrate-CoA ligase
adaptive e. induced e
allosteric e. an e. that exhibits the property of allosterism.
amino acid activating e. aminoacyl-tRNA synthetases
angiotensin-converting e. (ACE) a hydrolase responsible for the conversion of angiotensin I to the vasoactive angiotensin II by removal of a dipeptide (histidylleucine) from angiotensin I. Drugs that inhibit ACE are used to treat hypertension and congestive heart failure.
antitumor e. an e. that stimulates the degradation of a particular metabolite that cannot be synthesized by tumor cells, inhibits the synthesis of a metabolite needed by tumor cells, or inhibits tumor-specific DNA utilization; e.g., asparaginase.
autolytic e. an e. capable of causing lysis of the cell forming it.
branching e. 1,4-a-d-glucan branching enzyme
beta-carotene cleavage e. beta-carotene 15,15´-dioxygenase
citrate cleavage e. ATP citrate (pro-3S)-lyase
cold sensitive e. an e. that loses its stability as the temperature is lowered.
condensing e. citrate synthase
constitutive e. an e. that is constantly produced by the cell regardless of the growth conditions. Cf. induced e.
cooperative e. an e. that exhibits the property of cooperativity.
D e. 4-a-d-glucanotransferase
deamidizing e.'s amidohydrolases
deaminating e.'s deaminases
debranching e.'s e.'s that bring about destruction of branches in glycogen; formerly considered to be one enzyme, now known to be a mixture of transferases (4-a-d-glucanotransferase) and hydrolases (amylo-1,6-glucosidase).debranching factors;
digestive e.'s 1. e.'s that are utilized in the digestive system; 2. e.'s that are hydrolases of macromolecules (e.g., amylases, proteinases).
disproportionating e. 4-a-d-glucanotransferase
extracellular e. an e. performing its functions outside a cell; e.g., the various digestive e.'s.exoenzyme, lyoenzyme;
heat-stable e. thermostable e
hydrolyzing e.'s hydrolases
immobilized e. an e. that has been bound, usually covalently, to an insoluble organic or inorganic matrix or has been encapsulated.
induced e. , inducible e. an e. that can be detected in a growing culture of a microorganism, after the addition of a particular substance (inducer) to the culture medium, but was not detectable prior to the addition and can act on the inducer. A prototype is the beta-galactosidase of Escherichia coli, synthesized upon the addition of various galactosides, whether or not these are good substrates. Cf. constitutive e. adaptive e;
intracellular e. an e. that performs its functions within the cell that produces it; most e.'s are intracellular e.'s.endoenzyme;
Kornberg e. DNA polymerase I from Escherichia coli.
malate-condensing e. malate synthase
malic e. malate dehydrogenase
marker e. an e. that is used to identify a specific cell type, cell organelle, or cell component.
membrane e. an e. present or embedded in a biomembrane.
methionine-activating e. methionine adenosyltransferase
new yellow e. the d-amino-acid oxidase found in yeast, a flavoenzyme, which contains FAD as coenzyme instead of FMN as does NADPH dehydrogenase; so-called to distinguish it from Warburg's old yellow e. Cf. amino acid oxidases.
old yellow e. NADPH dehydrogenase
P e. phosphorylase
pantoate-activating e. pantothenate synthetase
phosphorylase-rupturing e. (PR e.) phosphorylase phosphatase
photoreactivating e. (PR e.) deoxyribodipyrimidine photolyase
PR e. abbreviation for phosphorylase-rupturing e.; photoreactivating e.
Q e. 1,4-a-glucan branching e. in plants.
R e. a-dextrin endo-1,6-a-glucosidase
reducing e. reductase
repair e. an e. that can catalyze the repair of damaged DNA; e.g., DNA ligase.
repressible e. an e. that is produced continuously unless production is repressed by excess of an inhibitor (corepressor). See also inactive repressor.
respiratory e. one of those e.'s in tissues that is a part of an oxidation-reduction system accomplishing the conversion of substrates to CO2 and H2O and the transfer of the electrons removed to O2.
restriction e. restriction endonuclease
RNA e. ribozyme
Schardinger e. xanthine oxidase
splitting e.'s e.'s that, like aldolases, catalyze the conversion of a molecule into two smaller molecules without the addition or subtraction of any atoms.
T e. 1,4-a-d-glucan 6-a-d-glucosyltransferase.
terminal addition e. DNA nucleotidylexotransferase
thermostable e. an e. that is not readily subject to destruction or alteration by heat.heat-stable e;
thiol e. an e. whose activity depends on a free thiol group.
transferring e.'s transferases
Warburg's old yellow e. NADPH dehydrogenase See also new yellow e., yellow e.
Warburg's respiratory e. Atmungsferment
yellow e. flavoenzyme See also Warburg's old yellow e., new yellow e.


Browse Medical References:

[A] [B] [C] [D] [E] [F] [G] [H] [I] [J] [K] [L] [M]
[N] [O] [P] [Q] [R] [S] [T] [U] [V] [W] [X] [Y] [Z]