Regulatory effect of phosphorylation of protein kinase C Apl I in the nervous system of Aplysia californica

Phosphorylation of calcium-activated protein kinase Cs (PKCs) at threonine 634 (T634) and/or threonine 641 increases during long-term potentiation or associative learning in rodents. We have raised an antibody to a peptide from PKC Apl I phosphorylated at T613 and T620 (sites homologous to T634 and T641). This antibody recognizes PKC Apl I only when it is phosphorylated at T613. Both phorbol esters and serotonin increase the percentage of kinase phosphorylated at T613 in Aplysia neurons. Furthermore, the pool of PKC that is phosphorylated at T613 in neurons is resistant to both membrane translocation and downregulation. Replacement of T613 with alanine increases the affinity of PKC Apl I for calcium, suggesting that phosphorylation of this site may reduce the ability of PKC Apl I to translocate to membranes in the presence of calcium. We propose that phosphorylation of this site is important for removal of PKC from the membrane and may be a mechanism for negative feedback of PKC activation