On the Mechanism of Activation of Phosphorylase b Kinase by Calcium

Kinase-activating factor, a protein required for the activation of phosphorylase b kinase by Ca++, was purified from brain tissue and from skeletal muscle and myocardium.All fractions contained calcium-activated proteinase activity as measured by the formation of acid-soluble, tyrosinepositive material with casein as substrate.The ratio of kinase-activating factor activity to proteinase activity remained constant throughout the purification, and both activities coincided on Sephadex G-100 filtration.Kinaseinhibitory factor, which prevents activation of kinase by Ca++, inhibited proteinase activity.Kinase-inhibitory factor also prevented the activation of kinase by trypsin.Acidsoluble, ninhydrin-positive material was formed during the activation of phosphorylase kinase by kinase-activating factor in the presence of Ca+f.It is concluded that kinaseactivating factor is a calcium-activated proteolytic enzyme, that kinase-inhibitory factor is a proteolytic inhibitor, and that activation of phosphorylase b kinase by Ca++ involves proteolysis.