Transferase, glycogen-UDPglucosyl

The specificity of rat-muscle glycogen-UDPglucosyl transferase has been examined by Goldemberg. A marked difference from starch-UDPglucosyl transferase is that adenosine 5- D-glucosyl pyrophosphate) is only 50% as effective as the uridine analog. In contrast to the rabbit-muscle enzyme, maltoheptaose (and maltosaccharides of DP 4, 5, 6, and 8) will slowly act as acceptors of low efficiency. Maltose and malto-triose are very inefficient acceptors, and at concentrations of 0.64 and... 

Details of many of the properties of glycogen-UDPglucosyl transferase are not yet available, although the activation by n-glucose 6-phosphate is intriguing. With yeast and rat-liver preparations, the activity is increased... 

Fig. 6.—Interconversion of Glycogen and n-Glucose by way of Glycogen Cycle. (Key (1), hexokinase-adenosine 5-triphospliate (2), phosphoglucomutaae (3),UDPG-pyrophoaphorylase (4), glycogen-UDPglucosyl transferase and branching enzyme (5), phosphorylase and amylo-l,6-glucosidase (6), D-glucose 6-phosphatase.)...

Since glycogen-metabolizing tissues contain phosphoglucomutase, UDPG-pyrophosphorylase, ° glycogen-UDPglucosyl transferase, and phosphorylase, the presence of a glycogen cycle has been proposed (see Fig. 6). In rat tissues, the levels of the individual, enzymic activities are... 

There is, therefore, no reason to doubt that the concurrent action of glycogen-UDPglucosyl transferase and branching enzyme could provide one pathway for the in vivo synthesis of glycogen. 

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