It has been shown that intracellular injection of
protein kinase C (
calcium/
phosphatidylserine/
diacylglycerol-dependent
protein kinase), purified from mammalian brain, or application of the
tumor-promoting
phorbol diester, 12-O-tetradecanoyl-13-phorbol
acetate (TPA), leads to an enhancement of
calcium currents in the bag cell neurons of Aplysia. We now present evidence of an endogenous
enzyme in bag cell neurons which is activated by TPA and which has properties similar to those of mammalian
protein kinase C.
Calcium/
phosphatidylserine/
diacylglycerol-dependent
protein kinase activity was found in both cytosolic and particulate fractions prepared from isolated clusters of bag cell neurons. This endogenous
enzyme phosphorylated an 87,000-dalton
protein from bovine brain, which appears to be a specific substrate for
protein kinase C, as well as several substrates present in cytosolic fractions prepared from isolated bag cell clusters. Similar results were obtained using preparations made from pooled head ganglia from Aplysia. The pharmacological properties of the
calcium/
phosphatidylserine/
diacylglycerol-dependent
protein kinase activity in the Aplysia nervous system were similar to those of
protein kinase C from mammalian tissues. Thus, the same group of endogenous substrate
proteins were phosphorylated when
diacylglycerol was replaced by TPA in cytosolic fractions prepared from isolated bag cell clusters. Non-
tumor-promoting
phorbols (4-alpha-phorbol, 4-alpha-phorbol-12,13-didecanoate, and 4-O-methyl-12-O-tetradecanoylphorbol-13-acetate) did not stimulate
protein phosphorylation in these preparations. Phosphorylation by the Aplysia
calcium/
phosphatidylserine/
diacylglycerol-dependent
protein kinase was inhibited by polymixin B
sulfate, by
calmodulin, and by the "
calmodulin antagonists"
trifluoperazine,
calmidazolium and
W7.(ABSTRACT TRUNCATED AT 250 WORDS)