Phosphorylase

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Related to Glycogen phosphorylase: glycogen synthase

phosphorylase

[fäs′fȯr·ə‚lās]
(biochemistry)
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.

Phosphorylase

 

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.

V. V. ZUEVSKII

References in periodicals archive ?
Utilization of glycogen phosphorylase BB measurement in the diagnosis of acute coronary syndromes in the event of chest pain.
Glycogen phosphorylase: control by phosphorylation and allosteric effectors.
From the data presented in the table 1, it was noticed that there is significant elevation in the glycogen phosphorylase level in the gill, muscle and liver of fish exposed to lethal and sublethal concentration of deltamethrin.
As the rate of glycogenolysis is regulated by glycogen phosphorylase (GP), inhibition of this key enzyme may constitute a therapeutic option for the treatment of type 2 diabetes.
Ischemia modified albumin, free fatty acids, whole blood choline, B-type natriuretic peptide, glycogen phosphorylase BB, and car diac troponin.
"Using deletion analysis and site-directed metagenesis we have identified promoter elements that regulate the glycogen phosphorylase gene during cell differentiation of Dictyostelium," Rutherford reports.
The length of the rays suggests that glycogen phosphorylase (GP) and glycogen synthase (GS) are positively correlated, but despite this, there is dramatic variation in the amount of stored glycogen.
In one project, the researchers use the cellular enzyme glycogen phosphorylase -- which normally liberates glucose units from huge, energy-storing starch molecules called glycogen when the cell needs more fuel--to run the reaction in reverse using a laboratory-made glucose derivative.
Inhibiting the enzyme glycogen phosphorylase blocks excess glucose release into the bloodstream.
Glycogen phosphorylase a (GP) activity was determined using an assay kit (Baoman, Shanghai, China) based on the coupled reactions of GP with phosphoglucomutase and glucose-6-phosphate dehydrogenase which resulted in the formation of NADPH.
Quantitative real-time PCR (qPCR) was performed to determine glucose transporter 1 (GLUT1), glucose transporter 2 (GLUT2), glucose transporter 3 (GLUT3), phosphofructokinase 1 (PFK1), lactate dehydrogenase A (LDHA), alanine aminotransferase 2 (ALT2), MCT4, muscle glycogen synthase (GYS1), and liver-type glycogen phosphorylase (PGYL) mRNA expression levels.
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.