High-Affinity Folate Binding in Leukocyte Lysate from Normal Subjects: Effect of Concentration of Binding Protein, Temperature and pH

Abstract

Folate binding in lysate prepared from leukocytes containing large amounts of the folate-binding protein was studied in equilibrium dialysis experiments (pH 7.4, 37 °C). Binding displayed positive cooperativity, and the binding affinity increased with decreasing concentration of binding protein (affinity constants in the range of 5 × 10⁹1/mol to 7 × 10¹⁰l/mol). Both phenomena could be interpreted in terms of ligand binding to a polymerizing system where the affinity of ligand for the oligomer is greater than its affinity for the polymer prevailing at high concentrations of the binding protein. Binding affinity was decreased at a low temperature (7 °C) and particularly at pH 5.0 where positive cooperativity also disappeared. The binder (M_r∼25,000–30,000) eluted in the front effluent after DEAE-Sepharose® CL-6B chromatography of the lysate at pH 6.3.

Engineering Tumor-Targeted Gadolinium Hexanedione Nanoparticles for Potential Application in Neutron Capture Therapy

“…For instance, Gd uptake efficiency at nanoparticles concentration of 360 µg/mL was about 82% at 37 °C and only 4.5% at 4 °C. Since ligand binding and uptake is dependent on temperature (Holm et al, 1981;Holm et al, 1983), the uptake of Gd nanoparticles by KB cells was likely an energy dependent process. The enhanced cellular uptake at 37 °C was attributed to endocytosis that was active at 37 °C but suppressed at 4 °C.…”