A high-affinity folate binding protein in human cerebrospinal fluid.

Binding of 3H-folic acid to a protein in human cerebrospinal fluid (CSF) was studied in equilibrium dialysis experiments at 37 degrees C and pH 7.4. The binding was of a high-affinity type (10(10) l/mol), and the relative molecular mass of the protein was 25,000 as determined by gel filtration. The concentration of folate binding protein in CSF, expressed as maximum folate bound per 1, was 0.3 nmol/l. This value was of the same order of magnitude as that of serum.