INTERACTION OF GLUCOSE AND METFORMIN WITH ISOLATED RED-CELL MEMBRANE

Isolated human erythrocyte membranes (red blood cell (RBC) ghosts) wer e incubated with glucose at 5, 10, 20 and 100 mmol/l concentrations, w ith insulin (0.01 to 200 mU/l) and metformin (GAS 657-24-9) (0.5 up to 50.0 mu mol/l). Binding studies with C-14-glucose and subsequent gel electrophoresis revealed 60 % of the radioactivity around band 4.2-4.5 at 5 mmol/l, whereas a random distribution of radioactivity over all protein bands of the RBC membrane was found at 20 mmol/l concentration after incubation for 30 min or 48 h. Metformin does not bind covalent ly to RBC membranes, however, after photochemical linkage of C-14-metf ormin via the aminoreactive linker azidophenylglyoxal the highest radi oactivity (21 %) was counted in the range of band 4.2-4.5. In parallel with an increase of order parameters of 5-doxyl stearic acid the thio l status of the membranes decreases as determined by monobromobimane f luorescence. 20 and 100 mmol/l concentrations of glucose decrease the reactivity of membrane thiois towards bromobimane significantly to 73 and 62 % of the controls.