Nonenzymatic glycosylation of normal and abnormal haemoglobin alpha chains.

The total amount of haemoglobin-bound glucose is determined by the chemical method for quantification of glycosylated haemoglobin, used in the control of diabetic patients. About 40 per cent of the measured amount of glucose is bound by the alpha chains of haemoglobin. The effect of substitution of alpha chains on the glycosylation of the abnormal and normal chains was investigated in a J Buda and G Pest heterozygote. Intact red blood cells were incubated in the presence of labelled glucose of 0.20 MBq/mumol specific activity and 35 mM concentration, and nonenzymatic glucose incorporation into normal and abnormal alpha chains was followed. By the help of fingerprinting and autoradiography of separated chains the distribution of the incorporated radioactivity was investigated. Based on the results we may conclude that (i) 65 per cent of incorporated glucose is bound to five peptides; (ii) the abnormal chain does not affect the glycosylation of the normal alpha chain; (iii) the substitution of a potent glucose binding site (alpha 61) does not affect the glycosylation of the other residues in the abnormal chain; (iv) the presence of the abnormal chain does not interfere with the diagnostic use of the chemical method for quantification of glycosylated haemoglobin.