The effect of hypoglycin on some parameters of glucose metabolism in the rat.

that they are unlikely to be complexes between protein phosphatase-I11 and/or the il and iz inhibitors. Muscle extracts which had been filtered through Sephadex G-25 were assayed for protein phosphatase activities in the presence of a quantity of i2 sufficient to inhibit protein phosphatase-I11 by 90 %. Inhibition of phosphorylase phosphatase and glycogen synthase phosphatases-1 and -2 was 80 %, demonstrating that at least 90 % of these three activities in muscle extracts, in the standard assay, are attributable to protein phosphatase-111. In contrast, when 32P-labelled phosphorylase kinase phosphorylated in both the aand B-subunits was used as a substrate, the release of [32P]Pi was inhibited by only 35 % in muscle extracts. This is consistent with previous results, which showed that a-phosphorylase kinase phosphatase activity in muscle extracts (not inhibited by i2) is greater than /?-phosphorylase kinase phosphatase activity (which is inhibitable by i2) (Antoniw & Cohen, 19766).