Immunoreactive folate-binding proteins from human saliva. Isolation and comparison of two distinct species.

摘要: Human saliva contains a single 72,000-M(r) species which specifically reacted with rabbit anti-[human placental folate receptor (PFR)] serum on SDS/PAGE and Western blots. Although specific radioimmunoassay for human PFR related folate-binding proteins (FBPs) identified 55 ng of cross-reacting material (CRM) per mg crude salivary proteins, only minor fraction (1.6 ng) bound radiolabelled folate. The major CRM did not contain endogenous bind folates. On the basis binding, to were designated as either functional (f-FBP) or non-functional (nf-FBP) respectively. nf-FBPs f-FBPs isolated by different purification schemes. Both purified migrated apparent SDS/PAGE, but Sephacryl S-200 gel filtration sucrose-density-gradient ultracentrifugation they eluted/sedimented 40,000-M(r) markers. Each microgram f-FBP nf-FBP was measured in being equivalent 18 24 respectively, indicating low epitope-relatedness PFR. Kd 50 pM 0.94 mol bound/mol protein. exhibited an unusual dependence Triton X-100 optimal ligand despite fact that micelle binding demonstrated. relative order affinity pteroylglutamate greater than methotrexate 5-formyltetrahydrofolate 5-methyltetrahydrofolate also distinct from Whereas amino acid carbohydrate analysis revealed (M(r) 51,400) 39,200) glycoproteins 8 13% isoelectric focusing immunological studies suggested some structural identity. presence normal raises new questions about their possible role vivo.