Glycogen synthetase in the sea mussel Mytilus edulis L.—I. Purification, interconversion and kinetic properties of the I and D forms

Abstract

1. 1. The two forms, I (active, independent of G6P) and D (inactive, dependent on G6P), of glycogen synthetase have been identified in Mytilus edulis. 2. 2. Incubation of a crude extract of the mantle enzyme at 30°C resulted in conversion of the D to I form due to endogenous phosphatase activity. 3. 3. The mantle enzyme was purified by affinity chromatography on Con A-Sepharose. The K m values for UDPG were 0.32 and 2.8 mM for the D and I forms of the enzyme, respectively. The K a for G6P, of the D form was 0.76 mM. 4. 4. Inorganic phosphate (2–10 mM) strongly inhibited the D form of glycogen synthetase. The inhibition was not reversed by increased concentrations of G6P (10 mM); in contrast, 5 mM G6P reversed the inhibition of the I form by inorganic phosphate.