Identification of a novel protein kinase C inhibitor in microsomes from phytohaemagglutinin activated human peripheral blood mononuclear cells.

Abstract A peptide inhibiting either corpuscolate or purified PKC has been identified from microsomes of PHA-activated human PBMC but it is not detectable in microsomes of resting PBMC. The peptide was obtained from a microsomal preparation in an oligomeric form that could be transformed into a monomeric form by β-MSH. The active peptide (IN) was retained on a PC-11 chromatographic column and could be eluted with Nad. IN is ineffective on PKC-dependent protamine phosphorylation of protamine and on Ca 2+ and phospholipid-independent activity generated by mild hydrolysis with trypsin of PK-C. Ca 2+ binding is permissive for IN activity. IN inhibits particulate PK.C in PHA-activated PBMC, but is ineffective after TPA activation. All these data indicate that IN acts at the regulatory domain of PKC.