Transcobalamin II in human seminal plasma.

Study of cobalamin-binding proteins revealed seminal plasma to be the most concentrated site of transcobalamin II in man. The next richest normal fluid, blood, has approximately one-tenth its concentration. Normal seminal unsaturated cobalamin-binding capacity averaged 15,030 +/- 7,290 pg/ml, of which 11,550 +/- 6,660 pg/ml was transcobalamin II. Transcobalamin II levels were markedly diminished in subjects lacking seminal vesicles (1520-1660 pg/ml), but not after vasectomy. This suggests that seminal vesicles are the chief source of this protein in semen. R binder concentration was increased in postvasectomy subjects (9,970 +/- 4,900 pg/ml vs. 2,980 +/- 1,370 pg/ml in normals) and varied in other patients. The endogenous cobalamin content of semen was only 88-699 pg/ml, and was carried largely by R binder rather than by transcobalamin II. The function of the unusually large seminal transcobalamin II pool in reproduction is unknown, but seems unlikely to be related solely to cobalamin transport needs, at least within the male reproductive tract itself.