title: Beta-microseminoprotein (beta-MSP) is not an inhibin.
abstract: Beta-microseminoprotein (beta-MSP), a sperm-coating antigen isolated from human seminal plasma, has apparent structural identity with "beta-inhibin" isolated from the same source. Publication of the amino acid sequence of beta-MSP revealed a greater than 96% homology with "beta-inhibin," with only a proline-threonine substitution at positions 39 and 40, and the omission of a glycine at position 93. Due to the nearly identical sequences of "beta-inhibin" and beta-MSP, we examined the ability of beta-MSP and its tryptic peptides to inhibit basal follicle-stimulating hormone (FSH) secretion from rat pituitary cells in culture, the inhibin bioassay. Whole pituitaries collected from 250- to 300-g male rats were dispersed enzymatically and plated onto 24-well culture dishes for 3 days. beta-MSP and its tryptic peptides were dissolved in cell culture medium, applied to the pituitary monolayer cell cultures, and incubated for an additional 3 days. FSH levels in the medium were determined by radioimmunoassay. A partially purified preparation of inhibin and our in-house inhibin standard, both prepared from porcine follicular fluid (pFFl), were included in the same assay. Whereas the partially purified inhibin from pFFl showed a dose-dependent inhibition of FSH secretion, with a 50% inhibitory dose (ID50) of 50 ng, which paralleled that of the standard, beta-MSP and its tryptic peptides failed to depress FSH levels in the medium at any of the doses tested (10-10,000 ng/ml). We conclude that beta-MSP is not an inhibin under our assay conditions.
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D005260:Female; D005640:Follicle Stimulating Hormone / Q000378:metabolism; D007265:Inhibins / Q000302:isolation & purification / Q000494:pharmacology; D008297:Male; D006080:Ovarian Follicle / Q000032:analysis; D010446:Peptide Fragments / Q000032:analysis; D010902:Pituitary Gland / Q000187:drug effects / Q000378:metabolism; D029584:Prostatic Secretory Proteins; D011506:Proteins / Q000302:isolation & purification / Q000494:pharmacology; D051381:Rats; D029589:Seminal Plasma Proteins; D013552:Swine; D013735:Testicular Hormones; D014357:Trypsin
chemical_list: D010446:Peptide Fragments; D029584:Prostatic Secretory Proteins; D011506:Proteins; D029589:Seminal Plasma Proteins; D013735:Testicular Hormones; C043076:beta-microseminoprotein; D007265:Inhibins; D005640:Follicle Stimulating Hormone; D014357:Trypsin