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An enzyme that catalyzes the formation of glucose-1-phosphate (Cori ester) from glycogen and inorganic phosphate; it is widely distributed in animals, plants, and microorganisms.



any of a group of transferase enzymes that catalyze the reversible reactions for the transfer of glycosyl groups (monosaccharide residues) to orthophosphate (phosphorolysis). The phosphorylase-catalyzed reaction may be expressed as follows:

where G is a glycosyl group, A is a glycosyl group acceptor, and O is orthophosphate. Seven enzymes are known that transfer hexose groups (from polysaccharides and disaccharides), and eight are known that transfer pentosyl groups (from nucleosides). These enzymes have a high degree of specificity relative to the glycosyl group; such specificity is not always observed, however, in the case of the acceptor.

Phosphorylases are widespread in nature, occurring in protozoans and in the tissues of animals and plants. They play an important role in organisms, catalyzing key reactions of metabolism related to the use of stored carbohydrates and, thus, to the supply of energy to cells. The study of phosphorylases has contributed to advances in enzymology. Phosphorylase-catalyzed reactions provided the model for research on macromolecular synthesis, the binding of an enzyme with a substrate, the allosteric regulation of enzyme activity, the dissociation of enzymes into subunits, and the catalytic conversion of an enzyme from an inactive form into an active form. The most thoroughly studied phosphorylases are those that catalyze the breakdown of gylcogen and starch, which are storage forms of carbohydrates.


References in periodicals archive ?
Immunoenzymometric assay of human glycogen phosphorylase isoenzyme BB in diagnosis of ischemic myocardial injury.
In mice, activation of AMPK by AICAR did not increase glycogen phosphorylase activity in postmortem muscle [7].
An investigation of the kinetic and anti-angiogenic properties of plant glycoside inhibitors of thymidine phosphorylase.
Glycogen phosphorylase labeling revealed a dramatic loss of cones under diabetic conditions, particularly in treatment paradigms that involved high glucose (Fig.
Oocyte Factors Suppress Mitochondrial Polynucleotide Phosphorylase to Remodel the Metabolome and Enhance Reprogramming," Cell Reports, 2015; DOI: 10.
Quantitative gene expression assays for excision repair (ERCC1), thymidine phosphorylase (TYMP), stathmin (STMN1), ribonucleotide reductase (RRM1) and other genes provide valuable information to help predict chemotherapy responses.
Pyridoxal 5'-phosphate is needed during exercise for gluconeogenesis and for glycogenolysis in which it serves as a cofactor for glycogen phosphorylase (21).
2 The concentration of thymidine phosphorylase is 3-10 folds higher in tumour cells compared to its concentration in the healthy tissues, and this can enable selective drug activation of 5-FU at the tumour site with limitation of systemic toxicity.
It could involve a group such as glycogen synthase, glycogen phosphorylase and phosphatase enzymes, and molecules such as ATP and protein type PEPCK.
The altered activities of the key enzymes of carbohydrate metabolism such as hexokinase, pyruvate kinase, lactate dehydrogenase, glucose-6-phosphatase, fructose-1,6-bisphosphatase, glucose-6-phosphate dehydrogenase, glycogen synthase and glycogen phosphorylase in liver of diabetic rats were significantly reverted to near normal levels by the administration of tangeretin.
Glycogen phosphorylase b is a stored, inactive form of the enzyme, and is activated to glycogen phosphorylase a to release glucose or phosphorylated glucose units from glycogen (Friedman 1985).