MODE OF THYROXINE ACTION IN ACTIVATION OF GLYCOGEN SYNTHETASE OF RANA CATESBEIANA TADPOLES

Tadpole-liver glycogen synthetase, which is completely dependent on glucose 6-phosphate, is activated by insulin. Activation involves transformation of the enzyme to a form with a lower Km for substrate, UDPG. Several factors mimic the hormone and activate the enzyme to a similar degree. These include thyroxine, dibutyryl cyclic 3′,5′-adenylic acid, theophylline, puromycin and clucose. In all case studied so far, a series of events which leads to the release of insulin is initiated. By using alloxan-treated and pancreatectomized tadpoles, we have shown that thyroxine activation of glycogen synthetase requires functional pancreatic β-cells to produce insulin. © 1969.