Interrelationship between ovine follicular fluid inhibin and serum albumin.

Ovine follicular fluid inhibin (oFF-I) as isolated in this laboratory, proved to be a monomeric protein (M(r).65 kDa). It was found to share very many of the physico-chemical characteristics of ovine serum albumin (oSA)-such as molecular size, iso-electric point, N-terminal aminoacid, finger-print patterns following enzymatic or cyanogen bromide cleavage, as well as binding of estradiol-17 beta and tryptophan. Furthermore, an antiserum containing polyclonal antibodies to oSA showed perfect cross-reaction with oFF-I. Nevertheless, oFF-I is distinct and different from oSA, as would be evident from the data reported here. Of the two proteins, oFF-I alone is capable of suppressing pituitary FSH output in a dose-dependent manner. Secondly, an antiserum containing polyclonal antibodies against Fraction-S2, a partially purified, biologically active fragment (M(r): 30-40 kDa)-derived from oFF-I, cross-reacted with the 65 kDa inhibin, but did not recognize oSA. Finally, the CD-spectra of the two proteins, when examined as a function of pH, show characteristic differences.