Phosphorylase

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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 ?
Starch phosphorylase activity was detected in the synthesis direction as described by Steup (1990).
Based on these observations, stolon starch phosphorylase activity declined following defoliation.
Starch phosphorylase activity was greater in stolons of control plants than in stolons of defoliated plants.
We thank Normand Brisson, Department of Biochemistry, University of Montreal, for the potato starch phosphorylase antibody.
Sweet-potato starch phosphorylase purification and characterization.
Effect of sodium cholate on the catalytic and structural properties of phosphorylase b.
Complete amino acid sequence of rabbit muscle glycogen phosphorylase.
The assay of glycogen phosphorylase in human blood serum and its application to the diagnosis of myocardial infarction.
Basal concentration of the isoenzyme BB of the glycogen phosphorylase b in human blood.

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