HEXOSE-SPECIFIC INHIBITION INVITRO OF HUMAN RED-CELL CA2+-ATPASE ACTIVITY

In a concentration-dependent manner (5.5-27.5 mmol/l), D-glucose incubated in vitro with human erythrocyte membranes at 37-degrees-C for 1 h inhibited membrane Ca2+-ATPase activity by up to 75%. The IC50 was 11 mmol/l. L-Glucose was ineffective, as were 3-O-methylglucose, 2-deoxyglucose, sorbitol and myo-inositol. In contrast, D-fructose decreased Ca2+-ATPase activity nearly as effectively as D-glucose and mannose and galactose at 11 mmol/l were less than 50% as effective as D-glucose. Tunicamycin (12 pmol/l), but not 10 mmol/l aminoguanidine, progressively antagonized in vitro the D-glucose effect on the enzyme. Erythrocyte membrane Ca2+-ATPase activity may be regulated by glycosylation, rather than nonenzymatic glycation.