Hyperglycaemia alters the physico-chemical properties of proteins in erythrocyte membranes of diabetic patients.

1. The dynamic properties of erythrocyte membranes in diabetic children and of control erythrocyte membranes subjected to in vitro glycation have been investigated by means of fluorescence quenching of membrane tryptophan residues and ESR spectroscopy. 2. The apparent distance separating the membrane protein tryptophan and the bound 1-anilino-8-naphthalenesulphonate (ANS) molecules was decreased in erythrocyte membranes from children with diabetes. This resulted in a significant increase of the maximum energy transfer efficiency in diabetic membranes. 3. The relevant alterations occurred in the above parameters due to the in vitro nonenzymatic glycosylation of control membranes. 4. These changes were accompanied by the decreased hw/hs parameter of MSL and the increased relative rotational correlation time (tau c) of ISL in diabetic membranes and in the membranes subjected to in vitro glycation. 5. The results suggest that the conformational changes in membrane proteins may occur at both the intrinsic and exposed thiol groups. 6. Both the in vivo and the in vitro data indicate that nonenzymatic glycosylation of membrane proteins may be the major factor attributable to the alterations in the dynamic properties of erythrocyte membrane in diabetic state.