Impaired enzyme-to-enzyme channelling between hexokinase isoenzyme(s) and phosphoglucoisomerase in rat pancreatic islets incubated at a low concentration of D-glucose.
It was recently proposed that in rat pancreatic islets exposed to 8.3 mM D-glucose, alpha-D-glucose-6-phosphate undergoes enzyme-to-enzyme channelling between hexokinase isoenzyme(s) and phosphoglucoisomerase. To explore the identity of the hexokinase isoenzyme(s) involved in such a tunnelling process, the generation of 3HOH from the alpha- and beta-anomers of either D-[2-3H]glucose or D-[5-3H]glucose was now measured over 60 min incubation at 4 degrees C in pancreatic islets exposed only to 2.8 mM D-glucose, in order to decrease the relative contribution of glucokinase to the phosphorylation of the hexose. Under these experimental conditions, the ratio for 3HOH production from D-[2-3H]glucose/D-[5-3H]glucose at anomeric equilibrium (39.7 +/- 11.6%) and the beta/alpha ratios for the generation of 3HOH from either the D-[2-3H]glucose anomers (70.9 +/- 12.6%) or the D-[5-3H]glucose anomers (59.6 +/- 12.4%) indicated that a much greater fraction of alpha-D-glucose-6-phosphate escapes from the process of enzyme-to-enzyme channelling in the islets exposed to 2.8 mM, rather than 8.3 mM D-glucose. These findings suggest, therefore, that the postulated process of enzyme-to-enzyme channelling involves mainly glucokinase.
Zhang
Ying
Y
Laboratory of Experimental Hormonology, Brussels Free University, Brussels, Belgium.
Jijakli
Hassan
H
Courtois
Philippe
P
Sener
Abdullah
A
Malaisse
Willy J
WJ
D000818:Animals; D001692:Biological Transport / Q000502:physiology; D019992:Databases as Topic; D004305:Dose-Response Relationship, Drug; D005260:Female; D005947:Glucose / Q000378:metabolism / Q000494:pharmacology*; D019298:Glucose-6-Phosphate / Q000378:metabolism / Q000494:pharmacology; D005956:Glucose-6-Phosphate Isomerase / Q000187:drug effects / Q000378:metabolism*; D006593:Hexokinase / Q000187:drug effects / Q000378:metabolism*; D066298:In Vitro Techniques; D007515:Islets of Langerhans / Q000187:drug effects / Q000201:enzymology* / Q000378:metabolism; D007527:Isoenzymes / Q000187:drug effects / Q000378:metabolism; D008954:Models, Biological; D051381:Rats; D017208:Rats, Wistar
D007527:Isoenzymes; D019298:Glucose-6-Phosphate; D006593:Hexokinase; D005956:Glucose-6-Phosphate Isomerase; D005947:Glucose