Purification and Characterization of the Low Molecular Weight Human Folate Binding Protein Using Affinity Chromatography

The low molecular weight folate binding protein (FABP) has been purified 10000-fold to a specific activity of 7.2 μg of pteroylglutamic acid (PGA) bound per mg of protein. This purified FABP represents two protein bands that bind PGA on polyacrylamide disc gel electrophoresis, elutes from DEAE-cellulose in 0.001 M phosphate buffer, stains positive with PAS, elutes from concanavalin A Sepharose affinity columns with methyl α-mannoside, and shows three major peaks (pI = 6.8, 7.5, 8.2) by isoelectric focusing. The binding of PGA to purified FABP is dependent on pH and is inhibited by urea. PGA bound to purified FABP is not available for uptake by HeLa cells. These data characterize purified FABP to represent two basic glycoproteins which bind folates by noncovalent bonds.