Metabolism of tritiated D-glucose in rat erythrocytes.
The metabolism of D-[U-14C]glucose, D-[1-14C]glucose, D-[6-14C]glucose, D-[1-3H]glucose, D-[2-3H]glucose, D-[3-3H]glucose, D-[3,4-3H]glucose, D-[5-3H]glucose, and D-[6-3H]glucose was examined in rat erythrocytes. There was a fair agreement between the rate of 3HOH production from either D-[3-3H]glucose and D-[5-3H]glucose, the decrease in the 2,3-diphosphoglycerate pool, its fractional turnover rate, the production of 14C-labeled lactate from D-[U-14C]glucose, and the total lactate output. The generation of both 3HOH and tritiated acidic metabolites from D-[3,4-3H]glucose indicated incomplete detritiation of the C4 during interconversion of fructose-1,6-bisphosphate and triose phosphates. Erythrocytes unexpectedly generated 3HOH from D-[6-3H]glucose, a phenomenon possibly attributable to the detritiation of [3-3H]pyruvate in the reaction catalyzed by glutamate pyruvate transaminase. The production of 3HOH from D-[2-3H]glucose was lower than that from D-[5-3H]glucose, suggesting enzyme-to-enzyme tunneling of glycolytic intermediates in the hexokinase/phosphoglucoisomerase/phosphofructokinase sequence. The production of 3HOH from D-[1-3H]glucose largely exceeded that of 14CO2 from D-[1-14C]glucose, a situation tentatively ascribed to the generation of 3HOH in the phosphomannoisomerase reaction. It is further speculated that the adjustment in specific radioactivity of D-[1-3H]glucose-6-phosphate cannot simultaneously match the vastly different degrees of isotopic discrimination in velocity at the levels of the reactions catalyzed by either glucose-6-phosphate dehydrogenase or phosphoglucoisomerase. The interpretation of the present findings thus raises a number of questions, which are proposed as a scope for further investigations.
Manuel y Keenoy
B
B
Laboratory of Experimental Medicine, Brussels Free University, Belgium.
Malaisse-Lagae
F
F
Malaisse
W J
WJ
D000143:Acids / Q000378:metabolism; D000818:Animals; D001786:Blood Glucose / Q000378:metabolism*; D004163:Diphosphoglyceric Acids / Q000097:blood; D004912:Erythrocytes / Q000378:metabolism*; D005947:Glucose / Q000737:chemistry; D007773:Lactates / Q000097:blood; D019344:Lactic Acid; D010084:Oxidation-Reduction; D051381:Rats; D014316:Tritium; D014501:Uranium
D000143:Acids; D001786:Blood Glucose; D004163:Diphosphoglyceric Acids; D007773:Lactates; D014316:Tritium; D019344:Lactic Acid; D014501:Uranium; D005947:Glucose