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We briefly review the metabolism of the chloroplast stroma, and describe the structural modelling technique of elementary modes analysis. The technique is applied to a model of chloroplast metabolism to investigate viable pathways in the light, in the dark, and in the dark with the addition of sedoheptulose-1,7-bisphosphatase (nor-mally inactive in the dark). The results of the analysis show that it is possible for starch degradation to enhance photosynthetic triose phosphate export in the light, but the reactions of the Calvin cycle alone are not capable of providing a sustainable flux from starch to triose phos-phate in the dark. . | Eur. J. Biochem. 270 430-439 2003 FEBS 2003 doi 10.1046 j.1432-1033.2003.03390.x Elementary modes analysis of photosynthate metabolism in the chloroplast stroma Mark G. Poolman1 David A. Fell1 and Christine A. Raines2 1 School of Biology and Molecular Science Oxford Brookes University Headington UK department of Biological Sciences University of Essex Colchester UK We briefly review the metabolism of the chloroplast stroma and describe the structural modelling technique of elementary modes analysis. The technique is applied to a model of chloroplast metabolism to investigate viable pathways in the light in the dark and in the dark with the addition of sedoheptulose-1 7-bisphosphatase normally inactive in the dark . The results of the analysis show that it is possible for starch degradation to enhance photosynthetic triose phosphate export in the light but the reactions of the Calvin cycle alone are not capable of providing a sustainable flux from starch to triose phosphate in the dark. When reactions of the oxidative pentose phosphate pathway are taken into consideration triose phosphate export in the dark becomes possible by the operation of a cyclic pathway not previously described. The effect of introducing sedoheptulose-1 7-bisphospha-tase to the system are relatively minor and we predict innocuous in vivo. We conclude that in contrast with the traditional view of the Calvin cycle and oxidative pentose phosphate pathway as separate systems they are in fact in the context of the chloroplast complementary and overlapping components of the same system. Keywords Calvin cycle computer modelling elementary modes analysis oxidative pentose phosphate pathway photosynthesis. Introduction Photosynthate metabolism The Calvin cycle is a set of some 13 enzyme catalysed reactions that serve to fix external CO2 making the carbon available to the rest of metabolism and using energy stored in the form of ATP and NADPH harvested by the light reactions. The entry point is the .
