Binding of tumor-promoting and biologically inactive phorbol esters to artificial membranes

Multilamellar liposomes formed of phospholipids bind [20-3H(N)]-phorbol 12,13-dibutyrate, the dissociation constant and maximal binding being comparable to those found in fibroblasts or epidermal cells. The relative capacity of distinct phorbol esters to compete with the labeled ligand was similar to their relative tumor-promoting capacity. It is proposed that the specific binding of phorbol esters to biological material may be accounted for by their insertion in the phospholipid domain of membranes.