Measurement of a folate binding protein from rat liver cytosol by radioimmunoassay

A radioimmunoassay has been developed for the folate binding protein from rat liver cytosol with a molecular weight of 150,000 which was recently purified to homogeneity (Suzuki, N., and Wagner, C., 1980, Arch. Biochem. Biophys.199, 236–248). This method has indicated that the binding protein (FBP-CII) is found primarily in the liver. A significant amount of FBP-CII was also found in the kidney and much reduced levels in spleen, serum, brain, lung, and heart. No FBP-CII could be detected in small intestine, skeletal muscle, or testes. Small amounts of cross-reacting material were found in the livers of mouse, dog, chick, and humans. Levels of FBP-CII were not decreased in the livers of folate-deficient rats. Assays of rat fetal liver and kidney 2 days prior to birth showed much lower levels which increased rapidly at birth. These data are consistent with the FBP-CII fulfilling a role as a folate storage protein in rat liver.