Enzyme-to-enzyme channelling in the early steps of glycolysis in rat pancreatic islets |
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Authors: | Malaisse W J Zhang Y Jijakli H Courtois P Sener A |
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Institution: | Laboratory of Experimental Hormonology, Faculty of Medicine, Brussels Free University, 808 Route de Lennik, B-1070 Brussels, Belgium. malaisse@ulb.ac.be |
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Abstract: | 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. |
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