A C-13 NUCLEAR-MAGNETIC-RESONANCE INVESTIGATION OF THE METABOLIC FLUXES ASSOCIATED WITH GLUCOSE-METABOLISM IN HUMAN ERYTHROCYTES

We have used [2-C-13]D-glucose and carbon-13 nuclear magnetic resonanc e (NMR) spectroscopy to investigate metabolic fluxes through the major pathways of glucose metabolism in intact human erythrocytes and to de termine the interactions among these pathways under conditions that pe rturb metabolism. Using the method described, we have been able to mea sure fluxes through the pentose phosphate pathway, phosphofructokinase , the 2,3-diphosphoglycerate bypass, and phosphoglycerate kinase, as w ell as glucose uptake, concurrently and in a single experiment. We hav e measured these fluxes in normal human erythrocytes under the followi ng conditions: (1) fully oxygenated; (2) treated with methylene blue; and (3) deoxygenated. This method makes it possible to monitor various metabolic effects of stresses in normal and pathological states. Not only has C-13-NMR spectroscopy proved to be a useful method for measur ing in vivo flux through the pentose phosphate pathway, but it has als o provided additional information about the cycling of metabolites thr ough the non-oxidative portion of the pentose phosphate pathway. Our e vidence from experiments with [1-C-13]-, [2-C-13]-, and [3-C-13]D-gluc oses indicates that there is an observable reverse flux of fructose 6- phosphate through the reactions catalyzed by transketolase and transal dolase, even in the presence of a net flux through the pentose phospha te pathway.