On the identity of bovine seminal plasma inhibin

Abstract

In light of current discussions on multiple forms of inhibin, it was thought of interest to ascertain the identity of the postulated ‘iso-hormones’ of bull seminal plasma inhibin (Chari et al., 1978). By subjecting the biologically active fraction, obtained by Sephadex G-100 gel filtration of bull seminal plasma acetone powder, to extensive dialysis in distilled water adjusted to pH 5.8, it was possible to remove the bulk of inert protein as a precipitate. The resulting active preparation could be readily fractionated by preparative iso-electric focusing in the pH range 4.0–6.5 yielding 2 distinct homogeneous peptides, α and β, capable of suppressing hCG-induced uterine weight increase in immature mice, in a ‘reversed Steelman-Pohley’ assay design. However, of these, a alone was able to suppress post-castrational serum gonadotropin rise in appropriate animal models. This peptide is highly acidic in nature (iso-electric point = 2.2) and has a molecular weight ( M r ) of 18200 and a Stokes radius of 1.90 nm. On the basis of currently available evidence, it is concluded that the molecule consists of a single peptide chain.