Human nitrogen balanceFig. Nitrogen balance is controlled by the free amino acid pool; Note: this nitrogen homeostasis is not a real 'stasis' but effectively experiences a high, but stable turn-over rate known as steady state equi-but stable turnover rate known as steady state equilibrium; the cycle between excreted and dietary N is of course closed by metabolism of microorganisms and plants. Voet, Fundamentals, 3rdInorganic nitrogen is taken up by the fungal extra radical mycelium and assimilated via nitrate reductase and the glutamine synthetase-glutamate synthase cycleglutamine synthetase-glutamate synthase cycle.BacteriaFungiBacteriaFungiPlantGovindarajulu, M., P. E. Pfeffer, et al. (2005). "Nitrogen transfer in the arbuscular mycorrhizal symbiosis." 435(7043): 819-823.Ornithine aminotransferase (OAT)ammonia channels (AMT)PlantBacterial nitrogen metabolismmetabolismVoet, Fundamentals, 3rdFig. 21.45Microbial nitrogen fixation by bacterial it i t d l bi initrogenase in root nodule symbiosis Fig. 21.40Voet, Fundamentals, 3rdNitrogenase complex of Azotobacter vinelandiiReduced P-clusterMo-FeclusterKlebsiella pneumoniaeMo-Fe clusterKlebsiella pneumoniaeVoet, Fundamentals, 3rdFig. 21.41The flow of electrons in the nitrogenase-catalyzed reduction of N2The flow of electrons in the nitrogenase-catalyzed reduction of N2.Voet, Fundamentals, 3rdFig. 21.43Assimilation and decomposition of ammonia(PLP dependent)T i ti tiTransamination reactionsVoet, Fundamentals, 3rdOn page 738Page 738Voet, Fundamentals, 3rdPyridoxal phosphate is a versatile coenzyme being used in enzymes catalyzing the following reactions by temporarily accepting the transferred reactant: - transamination decarboxylation-decarboxylation - deamination - racemization - aldole cleavage g- elimination and replacement reactions at βcarbons and γcarbons Voet, Fundamentals, 3rdAmino acid degradation and metabolic fate of end productsVoet, Fundamentals, 3rdFig. 21.6Urea cycleLithiLit lli L-ornithine L-citrulline Fig. Unusual amino acids not used for protein synthesis Fig. Structure of argininosuccinic acidFree NH3comes from deaminationSecond NH3comes from aspartateUrea formation from arginineVoet, Fundamentals, 3rdFig. 21.9Interaction between Krebs cycle and urea
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