Enzyme-to-enzyme channelling in the early steps of glycolysis in rat pancreatic islets.
The metabolism of D-glucose displays anomeric specificity in rat pancreatic islets. The aim of the present report is to investigate whether such a situation implies enzyme-to-enzyme tunnelling of metabolites in the early steps of glycolysis. For such a purpose, the modelling of alpha- and beta-D-glucose catabolism, itself based on available information concerning both the utilisation of these two anomers and the intrinsic properties of phosphoglucoisomerase, was first examined. According to a theoretical model with enzyme-to-enzyme channelling, the generation of 3HOH from D-[2-3H]glucose should be higher in islets exposed to beta-D-glucose rather than alpha-D-glucose, whilst the opposite situation should prevail in the case of D-[5-3H]glucose conversion to 3HOH. Experimental data collected in rat islets incubated for 60 min at 4 degrees C in the presence of either alpha- or beta-D-glucose mixed with tracer amounts of either alpha- or beta-D-[2- 3H]glucose and alpha- or beta-D-[5-3H]glucose indicate that the beta/alpha ratio for D-[2-3H]glucose conversion to 3HOH is indeed higher than the beta/alpha ratio for D-[5-3H]glucose conversion to 3HOH. These findings are consistent with the postulated enzyme-to-enzyme tunnelling of glycolytic intermediates between hexokinase isoenzyme(s), phosphoglucoisomerase and, possibly, phosphofructokinase.
Malaisse
W J
WJ
Laboratory of Experimental Hormonology, Faculty of Medicine, Brussels Free University, 808 Route de Lennik, B-1070 Brussels, Belgium. malaisse@ulb.ac.be
Zhang
Y
Y
Jijakli
H
H
Courtois
P
P
Sener
A
A
D000818:Animals; D004798:Enzymes / Q000378:metabolism*; D005260:Female; D005947:Glucose / Q000378:metabolism; D005956:Glucose-6-Phosphate Isomerase / Q000378:metabolism; D006019:Glycolysis; D007515:Islets of Langerhans / Q000201:enzymology / Q000378:metabolism*; D008956:Models, Chemical; D010732:Phosphofructokinase-1 / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D014316:Tritium; D014867:Water / Q000378:metabolism
D004798:Enzymes; D014867:Water; D014316:Tritium; D010732:Phosphofructokinase-1; D005956:Glucose-6-Phosphate Isomerase; D005947:Glucose