HIGH-AFFINITY FOLATE BINDING IN HUMAN PROSTATE

Binding of H-3-folate in Triton X-100 solubilized human prostate homogenate was of a high-affinity type and displayed apparent positive cooperativity typical of specific folate binding. Radioligand dissociation was slow at pH 7.4, but rapid at pH 3.5. Gel chromatography revealed two major folate binding proteins (M(r) almost-equal-to 100 and 25 kDa), but only one single band (M(r) almost-equal-to 65-70 kDa) was detectable on SDS-PAGE and immunoblotting with rabbit-anti human milk folate binding protein. Concentration of folate binding protein in prostate homogenate expressed as maximum H-3-folate binding was 1.10 nmol/g protein, and the cross-reactivity with rabbit-anti human milk folate binding protein serum was 15% as determined by an enzyme-linked immunosorbent assay (median values; n = 6).