YUANHUACIN-A IS A SELECTIVE ANTAGONIST OF PHORBOL ESTER RECEPTOR IN PROTEIN-KINASE-C

Protein kinase C with a molecular weight of 82 kD has been purified to electrophoresis homogenous from rat brain through a series of chromat ography columns including DE-52, Sepharose G-200 and phenyl-Sepharose. The enzyme possessed autophosphorylation activity. Yuanhuacin A inhib ited the H-3-phorbol-12, 13-dibutyrate (H-3-PdBu) binding of PKC with an IC50 value of 1.48 +/- 0.28 X 10(-8) mol/L when the concentration o f H-3-PdBu was 1.5 X 10(-9) mol/L (K(i) = 1.2 X 10(-8) mol/L). Yuanhua cin A inhibited the PdBu-stimulated PKC activity in the catalysis of t he phosphorylation of Histone III-S with an IC50 of 2.82 +/- 0.37 X 10 (-9) mol/L (PdBu = 10(-6) mol/L), while it had no effect on the basal and Ca2+-stimulated PKC activity in the same assay system. This result suggests that Yuanhuacin A is a selective antagonist of the phorbol e ster receptor in protein kinase C.