Glycogen starch phosphorylase

This enzyme [EC 2.4.1.1], also called phosphorylase, catalyzes the reaction of [(l,4)-o -D-glucosyl] with orthophosphate to produce [(l,4)-o -D-glucosyl] -i and a-D-glucose 1-phosphate. The name to be used with this enzyme is dependent on the naturally occurring substrate for example, glycogen phosphorylase, starch phosphorylase, maltodextrin phosphorylase, etc. 

Formation of glycogen chains by glycogen muscle phosphorylase and starch amylose by potato phosphorylase. 

Phosphorylases from animal, bacterial, and plant sources can be distinguished by their substrate preferences. Animal and bacterial phosphorylases prefer the short outer branches of highly branched cz-glucans, such as glycogen. The phosphorylase from Corynebacterium cal-luna, which accumulates a starch-like polysaccharide, is exceptional among bacterial enzymes... 

Glycogen in animal tissues and in microorganisms (and starch in plants) can be mobilized for use within the same cell by a phosphorolytic reaction catalyzed by glycogen phosphorylase (starch phosphorylase in... 

The formation of a branched polysaccharide, similar to glycogen, which is present in certain plants, especially waxy maize, has not yet been clarified however, it could be explained by interaction with starch phosphorylase or starch synthetase, causing branching. Neither the mechanisms for the separate formation of the linear and branched amylopectin components, nor the proportions of each in various plants, are known at present. These problems are undoubtedly a matter of genetic determinants that are awaiting future elucidation. 

Another common transfer reaction in carbohydrate enzymology is the transfer of an organic unit to inorganic phosphate (Pi). This type of reaction is catalyzed by phosphorylases such as starch phosphorylase or glycogen phosphorylase, and D-glucopyranosyl groups are transferred to Pi. 

Since D-fructose and D-glucose phosphates are amongst the first products of photosynthesis, and since starch (in plants) and glycogen (in animals) are converted by phosphorylase to D-glucosyl phosphate, biosynthesis of carbohydrates revolves around these ubiquitous compounds... 

The reaction catalyzed by phosphorylase. An oxygen of a phosphate ion attacks C-1 of the terminal glucosyl unit of starch or glycogen, displacing the macromolecule and generating glucose-1-phosphate. The reaction proceeds with retention of configuration, a fact... 

Figure 12-1 Phosphorylase-catalyzed phosphorolysis of glycogen or starch to glucose-1-phosphate.

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