High-affinity binding of folate to a serum protein in chronic myelogenous leukemia: effect of binder concentration, pH, and temperature.

Serum from a patient with chronic myelogenous leukemia was subjected to anion-exchange chromatography on DEAE-Sepharose CL-6B. High-affinity binding of [3H]folate to front effluent, eluted at a low salt gradient, was studied in equilibrium-dialysis experiments (37 degrees C, pH 7.4). As suggested by the data, folate binding displayed positive cooperativity. Dilution of the binder solution resulted in a shift to a simple non-cooperative binding type and increased binding affinity. Furthermore, binding was inhibited at pH 5.0 and at low temperature (7 degrees C). This study demonstrates important similarities between high-affinity folate binding in milk and serum: positive cooperativity and dependence of binding affinity on concentration of binder. Identical mechanisms may underly these phenomena in milk and serum. The apparent relationship between binding type and concentration of binder shown herein seems to agree fairly well with recent observations on sera from groups of healthy persons.