Decreased Ca2(+)-ATPase activity after glycosylation of erythrocyte membranes in vivo and in vitro.
Erythrocyte membranes drawn from diabetic patients with poor metabolic control have increased protein glycosylation and decreased Ca2(+)-ATPase activity. A significant relationship was found between these two parameters. Similar results were obtained when protein glycosylation and Ca2(+)-ATPase activity were measured in membranes from normal erythrocytes preincubated with glucose. In this condition, both parameters showed a clear time and dose dependence. Incubation of erythrocyte membranes instead of intact erythrocytes with glucose and glucose-6-phosphate strongly suggests that only the glycosylation of the membrane inner-surface proteins can affect Ca2(+)-ATPase activity. The simultaneous presence of 10 mM glucose and 5 mM ATP in the incubation medium did not affect the degree of erythrocyte membrane protein glycosylation but significantly blocked the inhibitory effect of glucose on Ca2(+)-ATPase activity. However, 5 mM ATP only partially blocked the inhibitory effect of 100 mM glucose, suggesting a competitive mechanism of glucose and ATP for the enzyme active site. Our results show that glycosylation of erythrocyte membrane proteins significantly inhibits Ca2(+)-ATPase activity. This effect could contribute to the development of the capillary closure process observed in diabetic patients. Furthermore, it could represent an index of a general impairment of enzyme function arising in cells chronically exposed to high glucose levels.
González Flecha
F L
FL
Institute of Chemistry and Biophysical Chemistry, Faculty of Pharmacy and Biochemistry, Buenos Aires University, Argentina.
Bermúdez
M C
MC
Cédola
N V
NV
Gagliardino
J J
JJ
Rossi
J P
JP
D000293:Adolescent; D000328:Adult; D001798:Blood Proteins / Q000378:metabolism; D000252:Calcium-Transporting ATPases / Q000097:blood*; D003470:Culture Media; D003922:Diabetes Mellitus, Type 1 / Q000097:blood; D004305:Dose-Response Relationship, Drug; D004910:Erythrocyte Membrane / Q000378:metabolism*; D005260:Female; D005947:Glucose / Q000494:pharmacology; D019298:Glucose-6-Phosphate; D005958:Glucosephosphates / Q000494:pharmacology; D006031:Glycosylation; D006801:Humans; D006863:Hydrogen-Ion Concentration; D006943:Hyperglycemia / Q000097:blood; D008297:Male; D008875:Middle Aged; D012016:Reference Values
D001798:Blood Proteins; D003470:Culture Media; D005958:Glucosephosphates; D019298:Glucose-6-Phosphate; D000252:Calcium-Transporting ATPases; D005947:Glucose