Abstract. Polyclonal isoenzyme-specific antisera were developed against four calcium-independent protein kinase C (PKC) isoenzymes (S, e, e', and~) as well as the calcium-dependent isoforms (a, 01, ßn, and -y).These antisera showed high specificities, high titers, and high binding affinities (3-370 nM) for the peptide antigens to which they were raised . Each antiserum detected a species of the predicted molecular weight by Western blot that could be blocked with the immunizing peptide . PKC was sequentially purified from rat brain, and the calcium-dependent forms were finally resolved by hydroxyapatite chromatography . Peak I reacted exclusively with antisera to PKCy, peak II with PKCß, and -ßu, and peak III with PKCa. These same fractions, however, were devoid of immunoreactivity for the calcium-independent isoenzymes. The PKC isoenzymes demonstrated a distinc-P ROTEIN kinase C (PKC)' plays a major role in transmembrane signal transduction (35). PKC is activated by diacylglycerol, which is generated from membrane phospholipids upon stimulation of cells with various agonists (4) . PKC also serves as the receptor for phorbol esters and related tumor promoters (34), which activate the kinase by substituting for endogenous diacylglycerol (8) . Because of the pleiotropic actions of diacylglycerol and phorbol esters, PKC has been implicated in the regulation ofa variety of cellular processes, including proliferation, differentiation, and release of hormones and neurotransmitters (35,36).Molecular cloning studies have revealed that PKC consists of a large family of at least eight different isoenzymes (36, 37) that can be divided into two major groups. Initially, four isoforms of PKC were described . This group consists of PKCca, -01, -ß, 1, and -y, with PKCß, and -ß arising via alternate splicing of the same gene transcript and resulting in distinct carboxy-terminal regions . All four of these isoen-1. Abbreviations used in this paper: PKC, protein kinase C.O The Rockefeller University Press,
