DETERMINATION OF THE FLUXES IN THE CENTRAL METABOLISM OF CORYNEBACTERIUM-GLUTAMICUM BY NUCLEAR-MAGNETIC-RESONANCE SPECTROSCOPY COMBINED WITH METABOLITE BALANCING

To determine the in vivo fluxes of the central metabolism we have deve loped a comprehensive approach exclusively based on the fundamental en zyme reactions known to be present, the fate of the carbon atoms of in dividual reactions, and the metabolite balance of the culture. No info rmation on the energy balance is required, nor information on enzyme a ctivities, or the directionalities of reactions. Our approach combines the power of H-1-detected C-13 nuclear magnetic resonance spectroscop y to follow individual carbons with the simplicity of establishing car bon balances of bacterial cultures. We grew a lysine-producing strain of Corynebacterium glutamicum to the metabolic and isotopic steady sta te with [1-C-13]glucose and determined the fractional enrichments in 2 7 carbon atoms of 11 amino acids isolated from the cell. Since precurs or metabolites of the central metabolism are incorporated in an exactl y defined manner in the carbon skeleton of amino acids, the fractional enrichments in carbons of precursor metabolites (oxaloacetate, glycer aldehyde 3-phosphate, erythrose 4-phosphate, etc.) became directly acc essible. A concise and generally applicable mathematical model was est ablished using matrix calculus to express all metabolite mass and carb on labeling balances. An appropriate all-purpose software for the iter ative solution of the equations is supplied. Applying this comprehensi ve methodology to C. glutamicum, all major fluxes within the central m etabolism were determined. The result is that the flux through the pen tose phosphate pathway is 66.4% (relative to the glucose input flux of 1.49 mmol/g dry weight h), that of entry into the tricarboxylic acid cycle 62.2%, and the contribution of the succinylase pathway of lysine synthesis 13.7%. Due to the large amount and high quality of measured data in vivo exchange reactions could also be quantitated with partic ularly high exchange rates within the pentose phosphate pathway for th e ribose 5-phosphate transketolase reaction. Moreover, the total net f lux of the anaplerotic reactions was quantitated as 38.0%. Most import antly, we found that in vivo one component within these anaplerotic re actions is a back flux from the carbon 4 units of the tricarboxylic ac id cycle to the carbon 3 units of glycolysis of 30.6%. (C) 1996 John W iley & Sons, Inc.