Kinetics of the D and I glycogen synthetase forms and their interconversion, in the sea scallop Pecten maximus

I. Vázquez-Baanante
M. Rosell-Pérez
47

Abstract

In extracts from the adductor muscle of the shell-fish, Pecten maximus, glycogen synthetase (EC.2.4.1.11) was found. The enzyme occurs predominantly as D form (glucose-06-P dependent for activity). An I form (G-06-P independent) was also present. Kinetics of glycogen synthetase showed that the Ka for G-06-P in the D form was 10 fold higher than in the I form. Both forms of glycogen synthetase were interconverted through reactions catalyzed by phosphatase and kinase enzymes respectively. Glucose-06-P and Mg+2 must be present to stabilize glycogen synthetase and to activate the synthetase D phosphatase, found in the 90,000 X g protein-glycogen complex. The conversion of synthetase D to I was inhibited by F-, glycogen, ATP and UTP. When F- was present the effect of G-06-P on synthetase and phosphatase suggested that conversion involved the existence of more than a single glycogen synthetase phosphatase enzyme. ATP and Mg+2 were necessary for the conversion of synthetase I to D, and the conversion was stimulated by cAMP.

Keywords:
Cyclic AMP/pharmacology, Glucose-06-Phosphatase/analysis/metabolism, Glycogen Synthase/metabolism, Magnesium/pharmacology, Mollusca/enzymology/metabolism, Uridine Diphosphate Glucose/pharmacology

Authors

I. Vázquez-Baanante
M. Rosell-Pérez


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