The intramolecular 13C‐distribution in ethanol reveals the influence of the CO2‐fixation pathway and environmental conditions on the site‐specific 13C variation in glucose

• DOI: 10.1111/j.1365-3040.2011.02308.x
• Publication Date: 2011-03-17T09:58:40Z
• Authors: ALEXIS GILBERT; VIRGINIE SILVESTRE; NICOLAS SEGEBARTH; GUILLAUME TCHERKEZ; CLAUDE GUILLOU; RICHARD J. ROBINS; SERGE AKOKA; GÉRALD S. REMAUD
• Keywords: 0301 basic medicine; 03 medical and health sciences

ABSTRACTEfforts to understand the cause of 12C versus 13C isotope fractionation in plants during photosynthesis and post‐photosynthetic metabolism are frustrated by the lack of data on the intramolecular 13C‐distribution in metabolites and its variation with environmental conditions. We have exploited isotopic carbon‐13 nuclear magnetic resonance (13C NMR) spectrometry to measure the positional isotope composition (δ13Ci, ‰) in ethanol samples from different origins: European wines, liquors and sugars from C3, C4 and crassulacean acid metabolism (CAM) plants. In C3‐ethanol samples, the methylene group was always 13C‐enriched (∼2‰) relative to the methyl group. In wines, this pattern was correlated with both air temperature and δ18O of wine water, indicating that water vapour deficit may be a critical defining factor. Furthermore, in C4‐ethanol, the reverse relationship was observed (methylene‐C relatively 13C‐depleted), supporting the concept that photorespiration is the key metabolic process leading to the 13C distribution in C3‐ethanol. By contrast, in CAM‐ethanol, the isotopic pattern was similar to but stronger than C3‐ethanol, with a relative 13C‐enrichment in the methylene‐C of up to 13‰. Plausible causes of this 13C‐pattern are briefly discussed. As the intramolecular δ13Ci‐values in ethanol reflect that in source glucose, our data point out the crucial impact on the ratio of metabolic pathways sustaining glucose synthesis.