Three distinct types of rat brain protein kinase C: their molecular heterogeneity and individual enzymological properties.

Abstract

Protein kinase C exists as a large family of multiple subspecies with subtle individual characteristics. Three types of protein kinase C designated type I, II, and III were purified from rat brain cytosol, which have been shown to correspond to the cDNA clones, gamma, beta, and alpha, respectively. Their relative activities in the whole brain tissue were found to be roughly 26%, 49%, and 25% with H1 histone as a substrate. Type II enzyme was an unequal mixture of two subspecies (roughly 1 : 7) encoded by beta I and beta II-sequences which differ from each other only in a short range of their carboxyl-terminal end regions. Although the three types have closely similar structures, they show a slightly different mode of activation and kinetic properties. Type I enzyme was sensitive to synthetic permeable diacylglycerol and significantly activated by low concentrations of free arachidonic acid. Type II enzyme exhibited substantial activity without elevated Ca2+ levels, and responded well to diacylglycerol and, to some extent, arachidonic acid. Type III enzyme shows nearly full activity in the presence of higher concentrations of arachidonic acid but is less sensitive to synthetic permeable diacylglycerol. The amino acid sequences predicted by cDNA analysis have indicated that the three types of protein kinase C have a tandem repeat of amino acid residues, that resemble the characteristic in "cysteine-zinc DNA-binding finger motif." Type I, but not type II or III enzyme could be activated by Zn2+ and showed some affinity for DNA-agarose, although its significance remains unclear. It is concluded that the three types of protein kinase C show subtle individual characteristics, and possibly play distinctly different physiological roles in signal transduction.