Catabolic half reaction

Using growing CHO 320 cells as the example of the advocated method, the growth reaction given in Equation (13) is divided into two half-reactions, namely the catabolic half-reaction. Equation (18), and the anabolic half-reaction. Equation (19),... 

Acceptance of Equation (20) means that, as stated in Section 2, the heat flux of the growth reaction is entirely reflected by that of the catabolic half-reaction (Equation (18)). The details of the methodology are too lengthy for inclusion in this Chapter and are given in Reference [105] but in essence the enthalpy of the catabolic half-reaction constructed as shown in Equation (18) is calculated in the way stated in Section 5.2.4 from the experimental reaction flux data. If this value balances the observed heat flux, then the complete description of the growth reaction is correct and the enthalpy recovery is unity. It should be remembered, however, that batch cultures are not in steady state. The metabolic activity and therefore the heat flux changes in terms of the environmental... 

All organisms use the same pair of pyridine nucleotides as carrier molecules for hydrogen and electrons. Both of these molecules accept hydrogen and electrons in the redox reactions of catabolism and become reduced. The oxidative half-reactions of catabolism generally produce two H+ and two electrons. The nicotinamide ring can accept two electrons and one H+ and, since the second H+ is released into the solution, most redox reactions in biological systems take the form ... 

Figure 53. Half cycles in dissipative maintenance metabolism with steady state ATP turnover, decoupled by futile cycling. The fhictose 6-phosphate/fructose 1,6-bisphosphate cycle is shown as an example. The net enthalpy change is calculated from the net biochemical change which, at steady state levels of ATP and all anabolic intermediates, is exclusively due to the catabolic half cycle reaction, equivalent to uncoupled catabolism (oxycaloric equivalent), Enthalpy is intermittently conserved in endothermic half cycles (p, phosphorylation a, anabolic), but an equivalent amount of enthalpy is exothermic in the reversed exergonic half cycles (-p, dephosphorylation d, dissipative). Therefore, ATP turnover and futile cycling raise the heat flux strictly proportional to the catabolic flux which, however, can be augmented by anaerobic catabolism with a corresponding anaerobic contribution to total heat flux (Reproduced from Reference [25] with permission).

Another catabolic enzyme, barbiturase, which catalyzed the hydrolysis of barbituric acid to urea and malonic acid (Fig. 23), has been purified partially (896). The mechanism involved in this reaction has not been established. Since it is unlikely that two linkages would be broken simultaneously in the same molecule by a single enzyme, it seems plaurible that the initial cleavage would have yielded a half ureide of malonic acid. So far there has been no evidence to suggest the formation of a half ureide of malonic acid. 

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