Demonstration of high molecular weight forms of inhibin in bovine follicular fluid (bFF) by using monoclonal antibodies to bFF 32K inhibin.

Monoclonal antibodies specifically recognizing each 20K and 13K subunit of bovine follicular fluid (bFF) 32K inhibin have been prepared. By immunoblotting procedures using these antibodies, we have demonstrated in bFF at least six inhibin forms, the apparent molecular weights of which are estimated to be 120K, 108K, 88K, 65K, 55K and 32K daltons, respectively. Amongst them 65K, 55K and 32K inhibin forms comprise two polypeptide subunits linked by disulfide bridge(s). In these inhibin forms a polypeptide of 13K daltons, a shorter subunit of bFF 32K inhibin, is attached by disulfide linkage(s) to polypeptides of 57K, 44K and 20K daltons, which are immunologically related to a larger subunit of the 32K inhibin, to yield 65K, 55K and 32K inhibins, respectively. On the other hand the higher molecular weight forms, 120K, 108K and 88K inhibins, are composed of three polypeptide subunits. In these forms a polypeptide of 62K daltons, immunologically related to the shorter subunit of bFF 32K inhibin, is attached by disulfide bridge(s) as the third component to the respective smaller inhibin forms which are composed of two subunits. These findings suggest that the complex formation of the subunit precursors may be extremely important and that restricted proteolytic cleavages following the complex formation may yield such divergent forms of inhibin in bFF.