Characterization of two isoforms of protein kinase C in the nervous system of Aplysia californica.

By molecular cloning Kruger et al. (Kruger, K. E., Sossin, W. S., Sacktor, T. C., Bergold, P. J., Beushausen, S., and Schwartz, J. H. (1991) J. Neurosci. 11, 2303-2313) provided evidence for three isoforms of protein kinase C (PKC) in Aplysia, two of which, Apl I and Apl II, are expressed abundantly in the nervous system. We resolve two major kinase activities from nervous tissue by column chromatography on DEAE-cellulose and hydroxylapatite (HAP), one Ca(2+)-activated and the other Ca(2+)-independent. We show that these two activities correspond to the previously cloned Apl I and II. These two isoforms appear to be the only major PKCs present in nervous tissue. The Apl I kinase is strongly activated by cis-fatty acids but only in the presence of Ca2+. Thus functionally, Apl I is more like the alpha and beta isoforms of vertebrate PKC, than to the vertebrate neural gamma isoform. The Apl II kinase is Ca(2+)-independent and resembles vertebrate PKC epsilon. The simplicity of the PKC isoform distribution in Aplysia makes this mollusc an attractive animal for understanding the differential regulation and physiological activities of Ca(2+)-activated and Ca(2+)-independent PKCs.