MODEL APPLICABLE TO NMR-STUDIES FOR CALCULATING FLUX RATES IN 5 CYCLES INVOLVED IN GLUTAMATE METABOLISM

Based on the same principles as those utilized in a recent study for m odeling glucose metabolism (Martin, G., Chauvin, M. F., Dugelay, S., a nd Baverel, G. (1994) J. Biol. Chem. 269, 26034-26039), a method is pr esented for determining metabolic fluxes involved in glutamate metabol ism in mammalian cells. This model consists of five different cycles t hat operate simultaneously. It includes not only the tricarboxylic aci d cycle, the ''oxaloacetate --> phosphoenolpyruvate --> pyruvate --> o xaloacetate'' cycle and the ''oxaloacetate --> phosphoenolpyruvate --> pyruvate --> acetyl-CoA --> citrate --> oxaloacetate'' cycle but also the ''glutamate --> alpha-ketoglutarate --> glutamate'' and the ''glu tamate --> glutamine --> glutamate'' cycles, The fates of each carbon of glutamate, expressed as ratios of integrated transfer of this carbo n to corresponding carbons in subsequent metabolites, are described by a set of equations, Since the data introduced in the model are microg rams of atom of traced carbon incorporated into each carbon of end pro ducts, the calculation strategy was determined on the basis of the mos t reliable parameters determined experimentally. This model, whose cal culation routes offer a large degree of flexibility, is applicable to data obtained by C-13 NMR spectroscopy, gas chromatography - mass spec trometry, or C-14 counting in a great variety of mammalian cells.