PHORBOL ESTER IN CONCENTRATIONS 10(-18)-1 0(-7)M INHIBITS LIPID-PEROXIDATION IN THE RAT-BRAIN PLASMA-MEMBRANES - EFFECT VIA PROTEIN-KINASE-C ACTIVATION

Effects of 12-O-tetradecanoylphorbol-13-acetate (TPA) and protein kina se C (PKC) in a broad range of concentrations (10(-18) - 10(-7) M) on the lipid peroxidation (LPO) in the rat brain plasma membranes were st udied, It was shown that TPA and PKC inhibit LPO; the concentration de pendence curves have two maxima at 10(-15) M and 10(-12) M for TPA and at 10(-16) M and 10(-13) M for PKC, During combined action of TPA (10 (-12) M) and PKC (10(-16) M), the synergism in LPO inhibition was obse rved. The data obtained indicate that PKC probably exhibits two enzyma tic activities, kinase and antioxidative, simultaneously, The properti es of TPA as an LPO inhibitor (via PKC activation) and tumor promoter (LPO inhibition is one of the necessary steps of tumor promotion) can be explained based on this suggestion.