Reduction of methemoglobin and ferricytochrome c by glycosylated amino acids and albumin.

The fraction of Amadori products gradually decreased during heavy glycosylation of amino acids and human serum albumin while the amount of a colored product with the maximum fluorescence at 420 nm decreased. The addition of the produced ketoamines of amino acids to the solution of native albumin quenched its own fluorescence due to generation of a Schiff base with amino groups of the protein. Carbonyl-containing Amadori products obtained during the early steps of glycosylation were less potent electron donors than amino acids more heavily modified by the carbohydrate. Under anaerobic conditions, glycosylated amino acids and human serum albumin reduced metHb and ferricytochrome c to ferroforms. In the presence of oxygen, the electron was transferred from glycosylated amino acids to ferriforms of the heme proteins and also to oxygen molecules with the generation of superoxide anions and hydrogen peroxide. Free oxygen radicals and hydrogen peroxide induced damage to the protein globule of Hb associated with the release of hemin, Fe(III) ions, and cleavage of the porphyrin ring.