Sphingomyelin is a possible constituent of binding sites for the tumor promoters phorbol ester, indole alkaloids and polyacetates.

Specific binding of 12-0-tetradecanoylphorbol-13-acetate to the epidermal particulate fraction was susceptible to phospholipase A2 and phospholipase C, but was almost resistant to protease and completely resistant to a mixture of several glycosidases. Of vesicles prepared from five phospholipids associated with the epidermal particulate fraction, sphingomyelin vesicles bound 12-0-tetradecanoylphorbol-13-acetate specifically and most effectively. This binding was inhibited by not only phorbol esters but also two other classes of tumor promoters, indole alkaloids and polyacetates. These results suggest that sphingomyelin is involved in the binding sites of tumor promoters to the cell membrane.