Li+-induced release of the folate binding protein from human granulocytes

Release of folate binding protein from human leucocytes suspended in isotonic NaCl was studied in experiments where folate binding activity of the suspending medium was determined by equilibrium dialysis (pH 7.4, 37 degrees C) against 3H-folate. Release from leucocytes containing particularly high concentrations of folate binding protein was significantly increased in the presence of 70 mmol/l Li+. The stimulated release was apparently not an osmotic phenomenon since no effect was observed with isomolar Na+/K+. The released protein resembled the folate binding protein in leucocyte lysate as to characteristics of radioligand binding, ionic properties and molecular size. Hence no transformation of the protein seemed to occur during Li+-induced release.