Glycosylation of hemoglobin in vitro: affinity labeling of hemoglobin by glucose-6-phosphate.
To determine the mechanism for the formation of hemoglobin A1c (Hb A1c) in vivo, we incubated human hemoglobin with glucose and metabolites of glucose. [14C]Glucose-6-phosphate (G6P) reacted readily with deoxyhemoglobin, and formed a covalent linkage. The reaction rate was considerably reduced in the presence of carbon monoxide or 2,3-diphosphoglycerate (2,3-DPG). Purified G6P hemoglobin had a lowered oxygen affinity and decreased reactivity with 2,3-DPG compared to Hb A. G6P behaved as a 2,3-DPG analog and reacted specifically at the NH2-terminal amino group of the beta chain. In contrast, the interaction of hemoglobin with glucose was much slower, and was unaffected by carbon monoxide or 2,3-DPG. Neither glucose-1-phosphate, fructose-6-phosphate, nor fructose-1,6-diphosphate formed a reaction product with hemoglobin. G6P behaves as an affinity label with the phosphate group forming electrostatic bonds at the 2,3-DPG binding site and the aldehvde group reacting with the NH2-terminal amino group of the beta chain. Thus, G6P hemoglobin may be an intermediate in the conversion of Hb A to Hb A1c.
D000595:Amino Acid Sequence; D002263:Carboxyhemoglobin; D055598:Chemical Phenomena; D002621:Chemistry; D004163:Diphosphoglyceric Acids / Q000378:metabolism; D005958:Glucosephosphates; D006441:Hemoglobin A / Q000378:metabolism; D006454:Hemoglobins / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D010100:Oxygen / Q000378:metabolism; D010108:Oxyhemoglobins
D004163:Diphosphoglyceric Acids; D005958:Glucosephosphates; D006454:Hemoglobins; D010108:Oxyhemoglobins; D006441:Hemoglobin A; D002263:Carboxyhemoglobin; D010100:Oxygen