Physicochemical and biological characterization of recombinant human inhibin A

Recombinant human inhibin A was isolated from recombinant mammalian cell line culture media. Two forms of inhibin were identified with Mr of 34 and 31 Kd composed of subunits (alpha, beta) of 24 and 15 Kd and 21 and 15 Kd respectively. Both forms are bioactive in an inhibin in vitro bioassay and immunoactive with potencies comparable to or higher than purified bovine inhibin. Amino acid analyses and NH2-terminal sequences of each of the subunits are consistent with those predicted from their cDNA structures. The inhibin alpha- but not beta-subunit is glycosylated based on its binding to the lectins concanavalin A and wheat germ lectin. The difference in molecular weight of 31 and 34 Kd inhibin is attributed to variation in glycosylation of the alpha-subunit. The 31+34 Kd inhibin is heterogeneous on isoelectric focusing gels consisting of four isoforms in the pH range 6.2-7.6. Inhibition also exhibits in vivo biological activity by suppressing serum FSH but not LH in castrate male rats. These physicochemical and biological characteristics of recombinant human inhibin are similar to those described for native inhibin isolated from a variety of other species.