Formate-producing pathway

As discussed herein, it can be concluded that the mechanistic pathways of the per-oxyoxalate system in the presence of imidazole are well described and that there is a consensus at least in regard to the steps prior to the formation of the HEI. Conventional kinetic studies on this complex transformation, with various consecutive and parallel reaction steps, permit the formulation of a mechanistic scheme, containing the important steps in the Tight-producing pathways, for which rate constants have been determined. Even so, the smdies concerning the EIEI strucmre are still controversial. Many authors favor 3 and/or 48 as the most probable candidates for the HEI, while others have suggested... 

The pentose-phosphate pathway. The early steps of the pentose-phosphate pathway are shown in detail as for a pentose-phosphate formation. This pathway produces two NADPHs and ribose-5-phosphate. The reformation of hexose phosphate involves C3,... 

Figure 28 Three putative reaction pathways of A/ -succinyiarginine dihydrolase. The urea (35)-forming pathway (a) is disfavored due to a iack of detectabie urease activity. Based on structural similarities to ADI enzymes, the N -succinylcitrulline (34)-forming pathway (b) has been proposed, but W -succinylcitrulline does not serve as an alternative substrate. The W -succinylornithine (32)-producing pathway (c) is consistent with the current data, but no intermediates have been isolated. An alternative pathway not shown is elimination of ammonia and retention of a covalent Cys365-S-(1-iminomethyl)-L-ornithine intermediate. In the final step of each pathway, the formation of bicarbonate or carbon dioxide has not been distinguished.

Two pathways have been described for formate metabolism a peroxidatic pathway via catalase and a folate dependent one carbon pathway. Treatment of rats with amino-triazole, an irreversible inhibitor of catalase, severely depressed a-oxidation activity but only slightly decreased the production of CO2 from exogenously added formate. " Whether the effect of aminotriazole is (solely) linked to the inhibition of catalase is unclear (see further). In addition to these above mentioned pathways our data point to a cytosolic NAD -dependent dehydrogenase activity that acts on the formate produced during a-oxidation. In peimeabilized cells or broken systems, suppUed with the qi-propriate cofactors (see further), almost no CO2 is formed, during a-oxidation unless NAD is added. ... 

Purification of drinking water by adding CI2 to kill bacteria is a source of electrophilic chlorine and contributes a nonenzymatic pathway for a chlorina tion and subsequent chloroform formation Al though some of the odor associated with tap water may be due to chloroform more of it probably results from chlorination of algae produced organic com pounds... 

Most of the enzymes mediating the reactions of the Calvin cycle also participate in either glycolysis (Chapter 19) or the pentose phosphate pathway (Chapter 23). The aim of the Calvin scheme is to account for hexose formation from 3-phosphoglycerate. In the course of this metabolic sequence, the NADPH and ATP produced in the light reactions are consumed, as indicated earlier in Equation (22.3). 

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