Inhibin in the male.

Abstract

Structure of Inhibin and Related Proteins Two forms of inhibin were isolated from ovarian follicular fluid. They are termed inhibin A and inhibin B to denote two differing glycoprotein hormones, which share a common subunit (a) and dissimilar subunits, respectively called 13A and 13B’ which formed disulfide-linked dimeric proteins with the capacity to suppress FSH secretion (de Kretser and Robertson, 1989). Inhibin A is thus noted as aI3 and inhibin B as aI3B. Each of the subunits is encoded by separate genes, which produce translated products, represented as pro-proteins, that are proteolytically cleaved during the synthesis of the dimer to produce a and 13subunits considerable smaller than the pro-proteins. Furthermore, free a subunits or products thereof are secreted from the sites of production, and some evidence exists that 13 subunit products may also occur. The monomeric products derived from the a subunit have been more carefully characterized and consist of pro-ac, aN, and a (Fig. 1) (Sugino et al, 1989). No evidence exists to indicate that the a subunit products are able to influence FSH secretion, but some data exist in the female to suggest that they may have some specific actions in the process of ovulation. The complexity of this field increased by the demonstration that dimers of the 13 subunit, termed activin A (l3Al3A) activin B (I3l3), and activin AB (I3A13B) have been isolated from a number of sources, including follicular fluid, and demonstrate the capacity to stimulate FSH