Binding of protein kinase C to neutrophil membranes in the presence of Ca2+ and its activation by a Ca2+-requiring proteinase

In the presence of micromolar concentrations of Ca²⁺, both protein kinase C and a cytosolic Ca²⁺-requiring neutral proteinase of human neutrophils become associated with the neutrophil membrane. Binding to the membrane results in activation of the proteinase, which then catalyzes limited proteolysis of the kinase to produce a form that is fully active in the absence of Ca²⁺ and phospholipid. This irreversibly activated protein kinase is released from the membrane and may thus have access, in the intact cell, to intracellular protein substrates. In the absence of proteinase, Ca²⁺ promotes the binding of protein kinase C, but conversion to the Ca²⁺/phospholipid-independent form does not occur and the kinase remains associated with the membrane fraction.