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Beta-Microseminoprotein (β-MSP) is not an Inhibin1

1987; Oxford University Press; Volume: 36; Issue: 4 Linguagem: Inglês

10.1095/biolreprod36.4.829

1529-7268

Wayne L. Gordon, Wan-Kyng Liu, Kazuko Akiyama, R Tsuda, Mitsuwo Hara, Karl Schmid, Darrell N. Ward,

Growth Hormone and Insulin-like Growth Factors

Beta-microseminoprotein (β-MSP), a sperm-coating antigen isolated from human seminal plasma, has apparent structural identity with “β-inhibin” isolated from the same source. Publication of the amino acid sequence of β-MSP revealed a greater than 96% homology with “β-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 “β-inhibin” and β-MSP, we examined the ability of β-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. β-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, β-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 β-MSP is not an inhibin under our assay conditions.