The effect of alpha-tocopheryl succinate (TS) on protein kinase C (PKC) activity was examined. TS increased the auto-phosphorylation of PKC in vascular smooth muscle cells. Furthermore TS activated isolated PKC-like phorbol 12-myristate 13-acetate (PMA), although it was required at a significantly higher concentration than PMA for PKC activation. Molecular superimposition of the TS on PMA by computation suggested that TS took an active binding conformation to the PKC-like PMA, but that the conformational population was about 1/1.000. Consequently, we conclude that TS interacts directly with PKC, and activates it by taking an active conformation like PMA.