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 ?
Botta et al., "Simplified analogues of immucillin-G retain potent human purine nucleoside phosphorylase inhibitory activity," Journal of Medicinal Chemistry, vol.
Glycogen phosphorylase (GP) is the enzyme responsible for the synthesis of glucose-1-phosphate, the source of energy for muscles and the rest of the body [31].
Abbreviations GS: Glycogen synthase GP: Glycogen phosphorylase PEPCK1: Phosphoenolpyruvate carboxykinase 1 G-6-Pase: Glucose-6-phosphatase GLUT2: Glucose transporter type 2 PGC-1[alpha]: PPAR[gamma] coactivator 1a AMPK: AMP-activated protein kinase ACC: Acetyl-CoA carboxylase TORC: Transducer of regulated CREB mTOR: Mammalian target of rapamycin CREB: cAMP-response element-binding protein.
Part 2: synthesis and biological evaluation of maslinic acid derivatives as glycogen phosphorylase inhibitors," Bioorganic and Medicinal Chemistry Letters, vol.
Identification and comparative analysis of thymidine phosphorylase in plasma of healthy subjects and cancer patients.
Transitory starch in the source leaf is degraded by starch degrading enzymes including amylase and starch phosphorylase. No difference was detected between the mutant and normal leaves for activity of either of these enzymes (Table 4).
Enzyme activity Ensyme C2-4 (normal) Ex139 (hls) units [g.zup.-1] protein Amylase 34.7 35.3 Starch phosphorylase 15.7 15.3 Hexokinase 0.95 1.01 Phosphoglucomutase 0.84 0.80 Phosphohexose isomerase 1.88 1.87 Phosphofruetokinase 0.84 0.83 Aldolase 6.9 6.5 Triosephosphate isomerase 125 126 Fructose-1,6-bisphosphatase 2.8 2.7 UDP glucose pyrophosphorylase 0.5 0.5 Sucrose-P phosphalase 18 17 Invertase 61.4 87.3 Significance Ensyme of t-test Amylase NS Starch phosphorylase NS Hexokinase NS Phosphoglucomutase NS Phosphohexose isomerase NS Phosphofruetokinase NS Aldolase NS Triosephosphate isomerase NS Fructose-1,6-bisphosphatase NS UDP glucose pyrophosphorylase NS Sucrose-P phosphalase NS Invertase (**) (*), (**) means significantly different at P = 0.05 and P = 0.01, respectively.
The starch degrading enzymes, amylase and starch phosphorylase, have been associated with transitory starch breakdown, but these had identical activities in his and normal-leaf plants, and identical native PAGE banding patterns.
These include: [Beta]-amylase (1,4-[Alpha]-D-glucan maltohydrolase) [EC 3.2.1.21, an exo-amylase that hydrolyzes starch from the nonreducing ends, producing maltose and [Beta]-limit dextrin; [Alpha]-amylase (1,4-[Alpha]-D-glucan glucanohydrolase) [EC 3.2.1.1], an endo-amylase that hydrolyzes starch by random hydrolysis of nonterminal glucosidic linkages to produce glucose, maltose, maltotriose, and branched oligosaccharides; [Alpha]-glucosidase ([Alpha]-D-glucoside glucohydrolase) [EC 3.2.1.20], which hydrolyzes maltose and other oligosaccharides to glucose, and starch phosphorylase (1,4-[Alpha]-D-glucan: orthophosphate [Alpha]-D-glucosyltransferase) [EC 2.4.1.1], which catalyzes in a reversible manner the formation of glucose-1-phosphate from starch and inorganic phosphate.
Starch phosphorylase activity was detected in the synthesis direction as described by Steup (1990).
Furosemide, at a final concentration of 0.1 mmol/L in serum-anti-[T.sub.3] antibody-furosemide solution, provided maximum [T.sub.3] displacement without interfering with the phosphorylase assay.
Effect of sodium cholate on the catalytic and structural properties of phosphorylase b.

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