C-13 NMR ISOTOPOMER AND COMPUTER-SIMULATION STUDIES OF THE NONOXIDATIVE PENTOSE-PHOSPHATE PATHWAY OF HUMAN ERYTHROCYTES

C-13 double-quantum filtered correlation spectroscopy (DQF-COSY) provides a novel method for the detection of reactions involving carbon-bond scissions. We report the use of this technique to investigate isotopic exchange reactions of the nonoxidative pentose phosphate pathway in human erythrocytes. These exchange reactions resulted in the formation of a range of isotopic isomers (isotopomers) of glucose 6-phosphate after incubation of a mixture of universally C-13-labelled and unlabelled glucose 6-phosphate with fructose 1,6-bisphosphate and haemolysates. These isotopomers were detected in the coupling patterns of cross-peaks within the DQF-COSY spectrum of the deproteinized sample. A computer model which fully describes the reactions of the non-oxidative pentose phosphate pathway in human erythrocytes has previously been constructed and tested with P-31 n.m.r. time-course data in our laboratory. This model was refined using C-13 n.m.r. time-course data and extended to include the range of isotopomers which may be formed experimentally by the reactions of the non-oxidative pentose phosphate pathway. The isotopomer ratios obtained experimentally from the DQF-COSY spectrum were consistent with simulations generated by this model.