Coupled metabolism

Amador JA, BF Taylor (1990) Coupled metabolic and photolytic pathway for degradation of pyridinedicarbox-ylic acids, especially dipicolinic acid. Appl Environ Microbiol 56 1352-1356. 

The maintenance of both the membrane potential and the steep gradients of ionic concentrations is essential to cells, both as a means of coupling metabolic energy to transport and other processes and for electrical signaling. The effects are most pronounced for mitochondrial membranes for which Em may attain -140 to -170 mV and for plasma membranes of excitable cells such as neurons (Em = -70 to -90 mV). For liver and kidney cells Em of plasma membranes maybe approximately - 35 mV and for erythrocytes only -9 mV.480... 

Sick, T.J., M. Perez-Pinon, P.L. Lutz, and M. Rosenthal (1993). Maintaining coupled metabolism and membrane function in anoxic brain A comparison between the turtle and rat. In Surviving Hypoxia, pp 351-363, ed. J.R. Sutton, C.S. Houston and G. Coates. Burlington, Vt. Queen City Printers. 

Figure 6.7 Enzymes coupling metabolism of PolyPs and nucleoside phosphates in bacteria (1) polyphosphate kinases (2) glucokinases (3) NAD kinases (4) PolyP AMP phosphotransferase (5) adenylate kinase.

To characterize the system, in terms of state-independent properties, we need to impose initial and boundary conditions, as well as concentrations of nutrients, enzymes, metabolites, mRNA, temperature, and pressure. The state-dependent properties include rates of free energy dissipation, rates of heat production, nutrient uptake flows, and growth rates. System biology requires quantitative predictions on the degree of coupling, metabolic consequences of gene deletion, attenuation, and overexpression. 

Tabata K, Koizumi S, Endo T, Ozaki A. Production of UDP-N-acetylglucosamine by coupling metabolically engineered bacteria. Biotechnol. Lett. 2000 22 479-483. 

Butta N, Urcelay E, Gonzalezmanchon C, Parrilla R, Ayuso MS. Pertussis toxin inhibition of -adrenergic or vasopressin-induced Ca2+ fluxes in rat-liver—selective-inhibition of the 0CJ-adrenergic receptor-coupled metabolic-activation. J Biol Chem 1993 268 6081-6089. 

For example, the induction of metabolizing enzymes by a chemical can greatly modify its PK and that of other substances, which is the subject of metabolic interactions [59], Intestinal barrier alterations due to intestinal toxicity can also affect PK [3]. Toxicity-induced retro-action mechanisms can also increase volumes of distribution The interaction of a chemical with aromatase can lead to a decrease in estradiol production and hence a decrease in FSH secretion, followed by a decrease in follicular growth and a reduction of the ovary volume [56], This should have implications for the design of in vitro assay systems. Integrated systems, such as those coupling metabolism and effect observations in human on chip micro-devices [5], offer a way to model experimentally the PK/PD continuum. 

TLC has been used to isolate and identify—at least by general chemical class—the potential mutagens. Again, the Salmonella histidine-reversion assay has been used to detect the activities, capitalizing on the ease of coupling metabolic activation to the system. 

Table X shows the inhibitory action of sodium azide and 2,4-dinitro-phenol on the accumulation of free glutamic acid within Slaph. aureus incubated with some of the derivatives listed in Table IX. In general all the systems studied are sensitive to the action of these uncoupling agents and no one system is markedly less sensitive than the others. This may mean that the accumulation process in all cases, even with diethylglutamic ester as source, involves some coupled metabolism.

Figure 52. Energy transformation half cycles in (a) fully coupled conservative metabolism, and (b) uncoupled catabolism, a Net synthesis of ATP in fully coupled metabolism. The enthalpy change per mol O2 is the sum of the catabolic (k, exothermic) and phosphorylation (p, endothermic) half cycle, b The dissipative catabolic half cycle provides the stoichiometric basis for calculating the oxycaloric equivalent, (Reproduced from Reference [25] with...

The direct incorporation of glutamic acid, as indicated by the dotted line on the structure, would account for the 2-8 coupling. Metabolism of the glutamate via the Krebs cycle could yield [2,3- C2]phosphoenol pyruvate, which is considered to be a precursor of C-5,6,7. Reformed glutamic acid after operation of the Krebs cycle could result in the observed couplings at 2-3 and 3-10. )... 

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