[Properties of phosphorylase kinase activated by subtilisin]

The activation of phosphorylase kinase during limited proteolysis by subtilisin was studied. It was shown that phosphorylase kinase undergoes rapid activation and its activity remains unchanged throughout a prolonged incubation. Electrophoresis in the presence of Na-SDS revealed a rapid decomposition of the alpha-subunit and a gradual disappearance of the beta-subunit; the protein molecule was shown to be composed of the degradation products of alpha- and beta-subunits with different molecular weights and unchanged proteolysis of the gamma-subunit. The phosphorylase kinase hydrolysate was separated using chromatography on a cellulose phosphate column. The active protein fraction contains a new form of phosphorylase kinase with a low molecular weight (approximately 80 000) which is insensitive to Ca2+. The subtilisin-activated phosphorylase kinase does not affect the activity of phosphodiesterase from cyclic nucleotides.