C-13 NMR evidence of the failure of human erythrocytes to metabolize ascorbate and dehydroascorbate to lactate

C-13-NMR spectroscopy was used to record time courses of the metabolism of [1-C-13]-L-ascorbic acid (AA) and [2-C-13]-L-ascorbic acid and their dehydr o-counterparts (DHAA) by human erythrocytes. Under a range of experimental conditions, but most notably in the absence of glucose in the incubation me dium, no C-13-NMR signal for lactate emerged during any of the 5 h time cou rses. The NMR resonances that did emerge over time were assigned to diketog ulonic (DKG) acid and CO2. Only very minor resonances from degradation prod ucts of DKG appeared from samples that contained physiologically high conce ntrations of DHAA. These results are in contrast with those in a recent rep ort that lactate is derived from AA in human erythrocytes. However, an expl anation for this possible artifact is given. (C) 2000 Elsevier Science Inc.