Glycosylated minor components of human fetal hemoglobin. Chromatographic separation, identification, and functional characterization.

Human adult red cell lysate contains glycosylated minor hemoglobins AIa1, AIa2, AIb, and AIc. Similar minor hemoglobins, designated FIa1, FIa2, Fib, and FIc, have been separated by a Biorex 70 column chromatographic procedure from red cell lysates of newborn children and from an adult homozygote for hereditary persistence of fetal Hb. The minor Hb components were characterized by analyzing for carbohydrate and phosphate contents, by oxygen equilibrium analysis, and by comparing the chromatographic elution profiles of naturally occurring and in vitro synthesized minor components. The results indicate that Hb FIa1, Hb FIa2, and Hb FIc have been formed by the modification of gamma chains of Hb F by reacting with fructose-1,6-P2, glucose-6-P, and glucose, respectively. Hb FIb is a glycoprotein; the mechanism of its formation is unclear. Hb FIa1 and Hb FIa2 had significantly lower oxygen affinities and n values than the other minor components and the major Hb F0. Moreover, 2,3-diphosphoglycerate did not influence the oxygenation of the minor or the major fetal Hb components. Incubations of Hb F with [14C]hexoses and subsequent chromatographic separation of hemoglobins and their globin chains confirm the previous findings that the binding of carbohydrate to Hb involves both specific and nonspecific reactions.