A homodimer of the beta-subunits of inhibin A stimulates the secretion of pituitary follicle stimulating hormone.

A 24,000 Dalton protein with follicle stimulating hormone (FSH)-releasing activity, named activin, has been characterized previously from porcine follicular fluid as a heterodimer composed of the beta-subunits of inhibins A and B linked by disulfide bond(s) [Ling et al. (1986) Nature, in press]. In this paper we report the isolation of another 24,000 Dalton protein with FSH-releasing activity from porcine follicular fluid, using successive steps of heparin-Sepharose affinity chromatography, gel filtration on Sephacryl S-200, and four steps of reversed-phase HPLC, followed by preparative sodium dodecyl-sulfate-polyacrylamide gel electrophoresis chromatography. Based on the molecular weight of the isolated molecule and its deduced NH2-terminal sequence, we propose that this second FSH-releasing substance present in porcine follicular fluid is a homodimeric protein composed of two beta-subunits of inhibin A joined together by disulfide bond(s). The name homo-activin-A is proposed for this substance.