Glycogen synthase in the mantle tissue of the freshwater snail Lymnaea stagnalis: Interconversion of kinetic forms and evidence for activity regulation by a concerted push-pull mechanism

Abstract 1. 1. Glycogen synthase (EC 2.4.1.11) from mantle tissue of Lymnaea stagnalis occurs in interconvertible kinetic forms. 2. 2. Transition to a carbohydrate-rich diet resulted in elevated haemolymph glucose levels and in activation of the enzyme as measured by changes in the activity ratio ( − G6P + G6P ) and the activation constant ( A 0.5 ) for G6P. 3. 3. Intracellular glucose levels in the mantle were highly variable, being a being a reflection of the haemolymph glucose levels. Glucose, however, had no direct effect on the activation state of glycogen synthase in mantle tissue in vitro , although it is known to stimulate glycogen synthesis. 4. 4. It is suggested that glycogen synthesis in the mantle is activated by a pull mechanism, implying interconversion of kinetic forms of glycogen synthase, and by a push mechanism via increased levels of metabolites.