Determination of the natural deuterium distribution in glucose from plants having different photosynthetic pathways

Abstract

The site-specific natural isotope fractionation of hydrogen in glucose was investigated by nuclear magnetic resonance spectroscopy (SNIF-NMR). Several glucose samples obtained from plants undergoing either C, (potato, barley, sunflower, wheat) or C4 (maize, sorghum) photosynthetic metabolism were investigated. Since the glucose molecule is not suitable for direct SNIF-NMR analysis, several kinds of derivatives were synthesized. Three clusters of isotopomers were identified in glucose penta-acetate which is easily prepared. Up to 5-6 sites could be distinguished in 6 other derivatives. An integrated statistical analysis of the whole sets of cluster lines was performed in order to determine the individual isotope contents in the carbon-bound hydrogen positions of the glucose skeleton. Both the mole fractions of the monodeuterated isotopomers and the deuterium/hydrogen ratios of the individual sites thus become accessible. Using this approach, it is shown that similar trends in the isotopic distribution are exhibited within a given photosynthetic C3 or C4 family. Larger deviations with respect to a statistical distribution of deuterium are observed in glucose from C3 plants as compared to C4 plants. The methylenic sites 6,6' in particular are significantly depleted in C, glucose as compared to C4 glucose.

Intramolecular deuterium distributions reveal disequilibrium of chloroplast phosphoglucose isomerase

“…This pattern is much less pronounced in bean endosperm starch, but deviations from a random distribution are still approximately 20%. As far as a comparison is possible, our results agree qualitatively with the results by Martin et al (1986) and Zhang et al (1994). The most striking effect in the spectra is the apparent depletion by approximately 40% of C(2)‐D of chloroplastic starch relative to sucrose or endosperm starch.…”

“…Derivatives of glucose have to be synthesized because the deuterium NMR spectra of glucose show poor resolution. Intramolecular D distributions of glucose were measured using deuterium NMR and were found to be non‐random (Martin et al 1986; Zhang et al 1994). However, in published derivatization procedures (Martin et al 1986; Williams et al 1993), at least two glucose derivatives have to be synthesized to measure the deuterium abundance of all seven carbon‐bound deuterium atoms, and gram amounts of sample are needed.…”

Detecting long-term metabolic shifts using isotopomers: CO2-driven suppression of photorespiration in C3plants over the 20th century

“…Although photorespiration leads to C loss, 3-phosphoglycerate (3-PGA) is formed after both carboxylation and oxygenation, but with differing stoichiometries and along differing paths. Numerous observations have shown that synthesis of a compound via different pathways induces different isotopomer distributions (18,19,(28)(29)(30)(31)(32). No exception to this rule has been observed, and it agrees with the theory of isotope effects.…”

Multi-factorialin vivostable isotope fractionation: causes, correlations, consequences and applications

“…The same must be true for other intermediates and final products. So, for example, although the Calvin cycle itself comprises only a sole reduction step, the glyceraldehyde phosphate dehydrogenase (GAPDH) reaction, glucose from different plants [174] and from different compartments within the same plant [175] has, depending on metabolic conditions, a slightly different and variable 2 H pattern of the C-bound hydrogen atoms. Details must be due to the complexity of sugar metabolism, the overlap of synthesis, glycolysis and gluconeogenesis.…”