Metabolism of tritiated D-glucose anomers in rat erythrocytes.
It was recently proposed that alpha-D-glucose 6-phosphate may undergo enzyme-to-enzyme channelling between glucokinase and phosphoglucoisomerase in rat pancreatic islets. The present study aims at exploring whether a different situation prevails in cells deprived of glucokinase, namely in erythrocytes. At anomeric equilibrium, the ratio between D-[2-3H]glucose and D-[5-3H]glucose conversion to 3HOH was lower in rat erythrocytes incubated for 60 min at 4 degrees C in the presence of 2.8 mM, rather than 8.3 mM, D-glucose. This coincided with both a greater relative increase in beta-D-[5-3H]glucose, as compared to alpha-D-[5-3H]glucose, conversion to 3HOH and an increase in the beta/alpha ratio for 3HOH generation from D-[5-3H]glucose in response to an increase in the anomeric concentration from 2.8 to 8.3 mM, the suppression of the difference between the beta/alpha ratios for 3HOH generation from D-[2-3H]glucose and D-[5-3H]glucose in the erythrocytes incubated at 8.3 mM, as distinct from 2.8 mM, alpha- and beta-D-glucose, and a [2-3H]/[5-3H] ratio for 3HOH generation lower than unity in erythrocytes exposed to alpha-D-glucose but not significantly different from unity in the presence of beta-D-glucose. These findings emphasize the relevance of alpha-D-glucose 6-phosphate channelling between hexokinase and phosphoglucoisomerase as a determinant of the difference between D-[2-3H]glucose and D-[5-3H]glucose conversion to 3HOH, and reveal that the regulation of such a tunnelling process by the concentration of the D-glucose represents, in rat erythrocytes, a mirror image of that observed in rat pancreatic islets. The regulation of this process thus tightly depends on the identity of the hexokinase enzyme mainly responsible for the phosphorylation of D-glucose in distinct cell types.
Zhang
Y
Y
Laboratory of Experimental Hormonology, Brussels Free University, Brussels, Belgium.
Jijakli
H
H
Courtois
P
P
Sener
A
A
Malaisse
W J
WJ
D000818:Animals; D004912:Erythrocytes / Q000201:enzymology*; D005260:Female; D005941:Glucokinase / Q000378:metabolism*; D005947:Glucose / Q000737:chemistry* / Q000378:metabolism*; D019298:Glucose-6-Phosphate / Q000378:metabolism*; D005956:Glucose-6-Phosphate Isomerase / Q000378:metabolism*; D007515:Islets of Langerhans / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D014316:Tritium
D014316:Tritium; D019298:Glucose-6-Phosphate; D005941:Glucokinase; D005956:Glucose-6-Phosphate Isomerase; D005947:Glucose