A phosphorylated enzyme cleaving poly(1,4-α-d-glucosyl)n with orthophosphate to form poly(1,4-α-d-glucosyl)n−1 and α-d-glucose 1-phosphate. SYN: α-glucan p., glycogen p., P enzyme, p. a, polyphosphorylase.
- p. a SYN: p..
- p. b dephosphorylated p. a. Under most conditions, the inactive form of p.; active in the presence of AMP. See p. phosphatase.
- p. kinase an enzyme that uses ATP to phosphorylate p. b and thus reform p. a, the active form of p.; the active form of p. kinase is itself a phosphorylated protein; upon dephosphorylation of p. kinase, the enzyme is inactivated; it can be rephosphorylated with a cAMP-dependent protein kinase; p. kinase is deficient in certain types of glycogen storage disease.
- p. phosphatase an enzyme catalyzing the conversion of one p. a into two p. b, with the release of four orthophosphates. SYN: p.-rupturing enzyme.

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phos·phor·y·lase fäs-'fȯr-ə-.lāz n any of a group of enzymes that catalyze phosphorolysis with the formation of organic phosphates (as glucose-1-phosphate in the breakdown and synthesis of glycogen) and that occur in animal and plant tissues

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any enzyme that catalyses the combination of an organic molecule (usually glucose) with a phosphate group (phosphorylation). Phosphorylase is found in the liver and kidney, where it is involved in the breakdown of glycogen to glucose-1-phosphate.

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phos·phor·y·lase (fos-forґə-lās) 1. any of a group of enzymes catalyzing phosphorolysis of glycosides, transferring the cleaved glycosyl group to inorganic phosphate. The term is usually qualified by adding the name of the substrate acted upon; when used alone it usually denotes glycogen phosphorylase (q.v.) in animals or starch phosphorylase in plants. 2. any of a group of transferases that catalyze the transfer of a phosphate group to an organic acceptor.

Medical dictionary. 2011.

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