Analytical studies on cobalamin-binding proteins of human seminal plasma

Abstract

Cobalamin-binding capacity of human seminal plasma amounted on average, to 23pmol/ml which was 20 times larger than that of serum. Most of the binding capacity was, in contrast to serum, unsaturated. Cobalamin-binders of seminal plasma separated into two distinct peaks on gel filtration; their elution positions and reactivity with antisera revealed that the largest portion of binding capacity is attributable to haptocorrin and the smaller portion to transcobalamin respectively. Total cobalamin-binding capacity and the ratio haptocorrin to transcobalamin varied significantly among samples examined. On column isoelectrofocusing, major peaks were seen at pH4.7 and 6.6; the former peak corresponding to 121 kDa reacted with an antihaptocorrin serum. One peculiar feature of the cobalamin-binder in seminal plasma is marked heterogeneity of components with pI below 4 as observed by the modified agarose-gel isoelectrofocusing technique. This suggested the presence of increased amounts of sialic acid residues on the binder molecule. The physiological role of cobalamin-binders in seminal plasma, such as the relationship to spermatogenesis, is still largely unknown. Detailed analysis of the binder may open up a new arena of cobalamin bioeffects.