Stimulation of muscle glycogen synthase phosphatase by polyamines

Abstract

The naturally-occurring polyamines were found to stimulate glycogen synthase phosphatase from rat skeletal muscle. The sequence of effectiveness in the stimulation was spermine >. spermidine > putrescine. It was shown that the spermine-sensitive phosphatase was present primarily in the soluble fraction of the muscle extract. In the presence of spermine, the phosphatase activity can be further stimulated by Mn 2+; however, a lower Mn 2+ concentration is required for the activation of the enzyme in comparison with that in the absence of spermine. Kinetic studies indicated that activation of glycogen synthase phosphatase by spermine was achieved by an increase in its V without significant alteration in the K m, suggesting that spermine directly stimulated the catalytic efficiency of the phosphatase enzyme.