Canadian Medical Guide > Chemicals and Drugs > Enzymes and Coenzymes > Enzymes > Multienzyme Complexes Terms and Definitions




Multienzyme Complexes

Medical Definition: Systems of enzymes which function sequentially by catalyzing consecutive reactions linked by common metabolic intermediates; may involve simply a transfer of water molecules of hydrogen atoms or be associated with large supramolecular structures such as mitochondria or ribosomes.
Also Called: Multifunctional Enzyme
Previously Indexed: specific enzymes or enzyme groups (1966-1973)
Multienzyme Complexes Categories.
Canadian Medical Guide Definition Anthranilate Phosphoribosyltransferase - An enzyme that catalyzes the formation of N-5'-phosphoribosylanthranilic acid from anthranilate and phosphoribosylpyrophosphate, the first step in tryptophan synthesis in E. coli. It exists in a complex with ANTHRANILATE SYNTHASE in bacteria. EC 2.4.2.18.
Canadian Medical Guide Definition Aspartate Carbamoyltransferase - An enzyme that catalyzes the conversion of carbamoyl phosphate and L-aspartate to yield orthophosphate and N-carbamoyl-L-aspartate. (From Enzyme Nomenclature, 1992) EC 2.1.3.2.
Canadian Medical Guide Definition Aspartokinase Homoserine Dehydrogenase - An enzyme complex consisting of aspartokinase, EC 2.7.2.4, and homoserine dehydrogenase, EC 1.1.1.3. The complex has been isolated from E. coli and consists of four identical subunits with a molecular weight of 85,000. The enzyme complex is involved in the biosynthesis of amino acids of the aspartate family.
Canadian Medical Guide Definition Electron Transport Chain Complex Proteins - A complex of enzymes and PROTON PUMPS located on the inner membrane of the MITOCHONDRIA and in bacterial membranes. The protein complex provides energy in the form of an electrochemical gradient, which may be used by either MITOCHONDRIAL PROTON-TRANSLOCATING ATPASES or BACTERIAL PROTON-TRANSLOCATING ATPASES.
Canadian Medical Guide Definition Fatty Acid Synthetase Complex
Canadian Medical Guide Definition Ketoglutarate Dehydrogenase Complex
Canadian Medical Guide Definition Lactose Synthase - An enzyme of the transferase class that catalyzes the transfer of galactose from UDPgalactose to glucose, forming lactose. The enzyme is a complex of the enzyme N-ACETYLLACTOSAMINE SYNTHASE and alpha-lactalbumin; the latter protein is present in lactating mammary gland cells where it alters the usual specificity of the former to make lactose synthesis the preferred reaction. (Dorland, 28th ed) EC 2.4.1.22.
Canadian Medical Guide Definition Phosphoenolpyruvate Sugar Phosphotransferase System - The bacterial sugar phosphotransferase system (PTS) that catalyzes the transfer of the phosphoryl group from phosphoenolpyruvate to its sugar substrates (the PTS sugars) concomitant with the translocation of these sugars across the bacterial membrane. The phosphorylation of a given sugar requires four proteins, two general proteins, Enzyme I and HPr and a pair of sugar-specific proteins designated as the Enzyme II complex. The PTS has also been implicated in the induction of synthesis of some catabolic enzyme systems required for the utilization of sugars that are not substrates of the PTS as well as the regulation of the activity of adenylate cyclase. EC 2.7.1.-.
Canadian Medical Guide Definition Photosynthetic Reaction Center Complex Proteins - Protein complexes that take part in the process of PHOTOSYNTHESIS. They are found in the THYLAKOID MEMBRANES of PLANTS and other photosynthetic organisms. There are two major complexes involved in the photosynthetic process called PHOTOSYSTEM I and PHOTOSYSTEM II.
Canadian Medical Guide Definition Prostaglandin-Endoperoxide Synthase - An enzyme complex that catalyzes the formation of prostaglandins from the appropriate unsaturated fatty acid, molecular oxygen, and a reduced acceptor. EC 1.14.99.1.
Canadian Medical Guide Definition Pyruvate Dehydrogenase Complex - A multienzyme complex responsible for the formation of ACETYL COENZYME A from pyruvate. The enzyme components are PYRUVATE DEHYDROGENASE C (LIPOAMIDE), dihydrolipoamide acetyltransferase and LIPOAMIDE DEHYDROGENASE. Pyruvate dehydrogenase complex is subject to three types of control: inhibited by acetyl-CoA and NADH; influenced by the energy state of the cell; and inhibited when a specific serine residue in the pyruvate decarboxylase is phoshorylated by ATP. PYRUVATE DEHYDROGENASE (LIPOAMIDE)-PHOSPHATASE catalyzes reactivation of the complex. (From Concise Encyclopedia Biochemistry and Molecular Biology, 3rd ed)

Multienzyme Complexes Medical Definitions and Terms

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