Isolation, characterization and possible mode of action of antiseminalplasmin, a new protein that inhibits the antimicrobial activity of seminalplasmin.

The isolation from bovine seminal plasma and purification of a new protein called 'antiseminalplasmin', which reverses the inhibition of the growth of, and RNA synthesis in, Escherichia coli by seminalplasmin (another protein of bovine seminal plasma), is described. Antiseminalplasmin, a weakly acidic protein, has a minimum Mr of about 39 000 and appears to consist of three acidic peptide chains that move close to each other on electrophoresis on cellulose acetate strips or on sodium dodecyl sulphate/18%-(w/v)-polyacrylamide gels. Antiseminalplasmin has a tendency to oligomerize at slightly alkaline pH values; it does not bind to seminalplasmin or to DNA, and does not reverse the inhibition by seminalplasmin of transcription in vitro by purified E. coli RNA polymerase. It appears that antiseminalplasmin may act by binding to the cell surface and preventing the entry of seminalplasmin into the cells. By itself, antiseminalplasmin has no effect on the growth of E. coli.