CHANGES IN GLYCOGEN SYNTHETASE AND PHOSPHORYLASE DURING MUSCULAR CONTRACTION

Tetanic contraction of rat skeletal muscle, previously stimulated to increase its glucose-6-P independent proportion of glycogen synthetase (I-GS), results in the transformation of GS from the independent to the dependent (D-GS) form. This I to D conversion is very rapid, since it takes place during the first 5 sec of stimulation, and occurs simultaneously with an increase of phosphorylase a. Possible mechanisms of this conversion have been investigated. During the ensueing recovery period glycogen phosphorylase is reverted to the less active b form, and GS to the more active I form. The simultaneous and opposite changes in the active forms of both enzymes are mantained, at least, through four cycles of contraction and recovery, suggesting the presence of a system which seems to interlook both enzymes to allow maximal efficiency during glycogenolysis or glycogenesis. © 1969.