The primary amino acid structures of the 43-kDa (A) and 15-kDa (B) subunits of the 58-kDa form of the hormone inhibin have been elucidated by cloning and analysis of cDNA species derived from bovine granulosa cell mRNA.The A subunit (Mr = 32,298) is a protein of 300 amino acids with two potential N-glycosylation sites and two potential proteolytic processing sites and'has a pre-pro region of 60 amino acids. The mature B sublinit (Mr = 12,977) is a protein of 116 amino acids synthesized from a separate mRNA. These data establish that a 31-kDa forn of inhibin also isolated from bovine follicular fluid, with subunits qf 20 kJa (Ac) and 15 kDa (B), is derived from the 58-kDa form by proteolytic processing of the A subunit.Considerable evidence has now accumulated to support the concept that the gonads produce a protein termed inhibin (1) that selectively suppresses the pituitary secretion of folliclestimulating hormone (2), a key hormone in controlling folliculogenesis and spermatogenesis. Controversy still exists concerning the nature of inhibin (3) partly because of the fact that some of the bioassays used in its characterization do not monitor follicle-stimulating hormone directly (4). For instance, inhibin-like activity has been detected in seminal plasma; the proteins associated with this activity have been purified and characterized but subsequently they were shown not to be of gonadal origin (5)(6)(7)(8)(9).We have isolated inhibin from a gonadal source, bovine follicular fluid, with an apparent molecular mass of 58 kDa, composed of two subunits now designated A and B, of 43 kDa and 15 kDa, respectively, linked together by disulfide bonds (10). Subsequently, 32-kDa inhibin was isolated by others from porcine follicular fluid, with two subunits of 18/20 kDa and 13/14 kDa (11,12). We have also shown that a 31-kDa form of bFF inhibin, composed of 20-kDa and 15-kDa subunits, is generated during a pH precipitation step in the purification procedure (13) but the precise relationship between the different forms has been unknown. However, the biological activity of the 31-kDa form is neutralized in vitro by an antiserum raised against the 58-kDa form (13), suggesting that the 31-kDa inhibin is a processed form of the 58-kDa inhibin.This article describes the amino acid sequences of the two subunits of the 58-kDa bovine inhibin as determined fromn cDNA sequencing and reports that the 20-kDa subunit of the 31-kDa inhibin is derived from the 43-kDa subunit of the 58-kDa inhibin, thus clarifying the relationship between these different forms.MATERIALS AND MIETIODS NH2-Terminal Amino Acid Sequencing of the 58-kDa Inhibin. The 58-kDa inhibin was isolated from bFF (10).Briefly, this involved a four-step' purjfication procedure: (i) gel permeation chromatography on Sephacryl 3200 in 0.05 M ammonium acetate, (it) gel permeation chromatography on Sephadex G100 in 4 M acetic acid, (iii) reversed-phase HPLC on an Ultrapore RPSC column-(Beckman) using a 0.1% trifluoroacetic acid-acetonitrile-H2O gradient, and (iv) prepara...

Inhibin is a gonadal hormone involved in the non-steroidal regulation of follicle stimulating hormone (FSH) secretion. Using the cDNAs coding for bovine inhibin A and B subunits we have identified inhibin genes within the human genome using Southern blot hybridisation techniques. The genes are likely to he present as single copies. Cloning and sequencing inhibin genes obtained from lambda libraries of human genomic DNA provide structural and sequence data on the human A and B genes. Comparison of the known inhibin gene sequences showed, in particular, that the B subunits have identical sequences in man, pigs and cattle thus demonstrating a remarkable evolutionary conservation in these genes.