Non-enzymatic glycosylation of protein: a form of molecular aging

Aldoses and ketoses react non-enzymatically with amino groups on proteins. The rates for individual amino groups differ widely. Hb AIc, the product of reaction of glucose and the N terminal amino group on beta chains, is normally present inside erythrocytes at about 4% of total haemoglobin. It is 3--5 fold increase in diabetics. Other fast haemoglobins are glycosylation products as well. The condensation between glucose and amino group first and rapidly leads to the formation of an aldimine (Schiff base) which then is slowly rearranged to give a ketoamine. The importance of the above reaction is outlined for other amino groups on haemoglobin and for many other proteins. Its role in the diabetic complications and in molecular aging in general is discussed.