Elucidation of novel biosynthetic pathways and metabolite flux patterns by retrobiosynthetic NMR analysis

The labelling patterns of metabolites from experiments with stable isotope‐labelled precursors can be determined by NMR spectroscopy. Complex isotopomer mixtures are found when general metabolites such as glucose are used as stable isotope‐labelled precursors which are diverted to all branches of intermediary metabolism. The complex results can be interpreted by a pattern recognition approach based on comparison between the labelling patterns of secondary metabolites and primary metabolites such as amino acids and ribonucleosides. The isotope labelling patterns of intermediates in central metabolic pools such as carbohydrate phosphates, dicarboxylic acids, and acetyl CoA can be obtained by biosynthetic retroanalysis. Biosynthetic pathways as well as metabolite flux patterns can be determined from these data. The method is illustrated using the classical mevalonate pathway and the more recently discovered deoxyxylulose pathway of terpenoid biosynthesis as examples. Applications of the retrobiosynthetic method of the biosynthesis of molybdopterin and of riboflavin are also discussed. Stable isotope experiments monitored by NMR spectroscopy have also been shown to be a powerful tool for the elucidation of metabolic flux in microorganisms with unusual lifestyles and in fermentation processes.