Indirect observation by 13C NMR spectroscopy of a novel CO2 fixation pathway in methanogens.

High-field carbon-13 nuclear magnetic resonance (NMR) spectroscopy has been used to monitor the isotopic dilution of doubly carbon-13-labeled precursors for 2,3-cyclopyrophosphoglycerate, a novel primary metabolite that occurs in certain methanogens. A unique carbon dioxide fixation pathway that gives rise to asymmetric labeling of acetyl coenzyme A has been demonstrated in Methanobacterium thermoautotrophicum. The effect of selected metabolic inhibitors on the labeled species in the pathway has been examined by NMR. These techniques establish a general, sensitive method for the delineation of convergent biosynthetic pathways.