Interaction of protein kinase C with chromaffin granule membranes: effects of Ca²⁺, phorbol esters and temperature reveal differences in the properties of the association and dissociation events

Interaction of protein kinase C with chromaffin granule membranes has been studied as a means of investigating the translocation of protein kinase C from cytosol to intracellular membrane surfaces, which is believed to occur during secretion. Protein kinase C in an adrenal medullary soluble fraction was found to bind reversibly to granule membranes in a Ca²⁺-dependent fashion. Association and dissociation events were sensitive to Ca²⁺ concentrations in the low micromolar range, and the Ca²⁺ sensitivity of both processes was increased when the membranes had been preincubated with the protein kinase C-activating phorbol ester, 4ß-phorbol 12-myristate 13-acetate (TPA). Binding of protein kinase C to granule membranes occurred at 0 and 37°C, irrespective of whether the membranes had been preincubated with TPA. However, dissociation of protein kinase C from granule membranes that had been preincubated with TPA occurred only at 37°C and not at 0°C, even though dissociation of the enzyme from membranes which had not been preincubated with TPA would occur at both 37 and 0°C. These effects of TPA were not reproduced by 4α-phorbol 12,13-didecanoate (4αPDD), a phorbol ester which does not activate protein kinase C. Soluble protein kinase C activity also associated with chromaffin granules in a Ca²⁺-dependent manner in an adrenal medullary homogenate, indicating that granules can compete with other intracellular membranes for the binding of protein kinase C. Results obtained with this model system differ from other systems where the interaction of protein kinase C with plasma membranes has been studied and have general implications for studies performed on the translocation of protein kinase C in intact cells and for the role of protein kinase C in stimulus-secretion coupling in the chromaffin cell.