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Physiological activation of protein kinase C requires the interaction of this enzyme with cellular membranes [Nishizuka (1986) Science 233,[305][306][307][308][309][310][311][312]. In the present work a reconstituted system of protein kinase C and human inside-out erythrocyte vesicles was utilized to study the effect in vitro of naturally occurring polyamines on the activation process of protein kinase C. The active membrane-associated complex was conveniently determined by its ability to bind radioactive phorbol ester with an exact 1: 1 stoichiometry. The association reaction of the enzyme to membrane was rapid, being complete within 1 min at 25 'C. The addition of polyamines, particularly spermine, greatly decreased in a dose-dependent manner the amount of protein kinase C bound to membranes (i.e. in the activated form). The effect observed was quite specific, since it was dependent on the chemical structure of the polyamine and it was manifest at micromolar concentrations of the polycation; the order of potency was spermine > spermidine > putrescine. A characterization of this effect is presented and possible physiological implications are discussed.