Glucan phosphorylase [Carbohydrate transport and metabolism]

glycogen phosphorylase; Provisional

This is a family of oligosaccharide phosphorylases. It includes yeast and mammalian glycogen phosphorylases, plant starch/glucan phosphorylase, as well as the maltodextrin phosphorylases of bacteria. The members of this family catalyze the breakdown of oligosaccharides into glucose-1-phosphate units. They are important allosteric enzymes in carbohydrate metabolism. The allosteric control mechanisms of yeast and mammalian members of this family are different from that of bacterial members. The members of this family belong to the GT-B structural superfamily of glycoslytransferases, which have characteristic N- and C-terminal domains each containing a typical Rossmann fold. The two domains have high structural homology despite minimal sequence homology. The large cleft that separates the two domains includes the catalytic center and permits a high degree of flexibility.

glycogen/starch/alpha-glucan phosphorylases. This family consists of phosphorylases. Members use phosphate to break alpha 1,4 linkages between pairs of glucose residues at the end of long glucose polymers, releasing alpha-D-glucose 1-phosphate. The nomenclature convention is to preface the name according to the natural substrate, as in glycogen phosphorylase, starch phosphorylase, maltodextrin phosphorylase, etc. Name differences among these substrates reflect differences in patterns of branching with alpha 1,6 linkages. Members include allosterically regulated and unregulated forms. A related family, TIGR02094, contains examples known to act well on particularly small alpha 1,4 glucans, as may be found after import from exogenous sources [Energy metabolism, Biosynthesis and degradation of polysaccharides].

Carbohydrate phosphorylase. The members of this family catalyze the formation of glucose 1-phosphate from one of the following polyglucoses; glycogen, starch, glucan or maltodextrin.