Cofactor in serum for high-affinity folate binding in milk.
Affinity-chromatographic purification of the folate-binding protein from whey of cow's milk results in the removal of a heat-resistant cofactor that is important in high-affinity folate binding (Biochim, Biophys. Acta 579: 479, 1979). Thus a shift from negative to positive cooperativity occurred in the presence of cofactor (Biochim, Biophys. Acta 579: 479, 1979). We demonstrate the presence of a similar cofactor in sera from men, pregnant women, and umbilical cords. Even highly diluted (10 000-fold) serum samples were active, and the cofactor was also present in erythrocyte hemolysates (10 000-fold diluted). The identity of the cofactor, which may act as an overall modulator of high-affinity folate binding, is still obscure.
D000818:Animals; D001798:Blood Proteins / Q000378:metabolism; D002352:Carrier Proteins / Q000302:isolation & purification*; D002417:Cattle; D002846:Chromatography, Affinity; D005260:Female; D058973:Folate Receptors, GPI-Anchored; D005492:Folic Acid / Q000302:isolation & purification* / Q000378:metabolism; D006801:Humans; D008297:Male; D008892:Milk / Q000032:analysis*; D011247:Pregnancy; D011956:Receptors, Cell Surface
D001798:Blood Proteins; D002352:Carrier Proteins; D058973:Folate Receptors, GPI-Anchored; D011956:Receptors, Cell Surface; D005492:Folic Acid