Oxidation branches

Fig. 17. Cyclic voltammogram of the water-soluble Rieske fragment from the bci complex of Paracoccus denitrificans (ISFpd) at the nitric acid modified glassy carbon electrode. Protein concentration, 1 mg/ml in 50 mM NaCl, 10 mM MOPS, 5 mM EPPS, pH 7.3 T, 25°C scan rate, 10 mV/s. The cathodic (reducing branch, 7 < 0) and anodic (oxidizing branch, 7 > 0) peak potentisds Emd the resulting midpoint potential are indicated. SHE, standEU d hydrogen electrode.

Characterization results have been reported for dendrigraft-polylpthylene ox-ide)s of generation Gl, prepared by adding different amounts of ethylene oxide to the initiator core in the side chain growth reaction (Table 9.8). Because of the grafting from method used, the molecular weight of the polyethylene oxide) branches cannot be accurately determined, and hence it is impossible to confirm... 

In the oxidative branch of malate dismutation, malic enzyme oxidizes malate to pyruvate, which is then further oxidized to acetyl-CoA by pyruvate dehydrogenase, an enzyme complex specially adapted to anaerobic functioning in Ascaris suum and possibly in other parasitic helminths like the trematode F. hepatica and the cestode Dipylidium caninum (Diaz and Komuniecki, 1994 Klingbeil et al., 1996). Parasitic helminths like F. hepatica use an acetate succinate CoA-transferase (ASCT) for... 

The results shown in Figures 7 and 9 also indicate that the sensors based on the poly(ethylene oxide) and siloxane-ethylene oxide branch polymer systems can operate efficiently at relatively low applied potentials. In fact, the sensors containing these polymers show steady-state glucose responses at a potential of +100 mV (vs. SCE) which are similar to the response of the best poly(siloxane)-based sensor at +300 mV. This is an important consideration because lower operating potentials are often advantageous in real measurements, where easily oxidizable interfering species are usually present. 

It is clear from these results that the ability of the redox polymers to mediate electron transfer from reduced choline oxidase is dependent upon the structure of the polymer backbone. The trend in mediating efficiency is qualitatively the same as that found for the glucose sensors siloxane-ethylene oxide branch polymer > poly(ethylene oxide) > poly(siloxane). 

It is likely that pyruvate, the product of the oxidative branch of the mitochondrial dismutation reaction, is further metabolised in cestodes to acetyl-CoA by oxidation with NAD+, as catalysed by the lipoamide-dependent mitochondrial pyruvate dehydrogenase complex. This enzyme has been reported in H. diminuta (935) and S. solidus (406). The acetyl-CoA is then hydrolysed to acetate. During this step, ATP synthesis may occur through the conservation of the acetyl-CoA energy-rich thioester bond by the combined action of an acyl-CoA transferase and a thiokinase (398) as follows ... 

As shown in Figure 8.4, the synthesis of NAD from tryptophan involves the nonenzymic cyclization of aminocarhoxymuconic semialdehyde to quinolinic acid. The alternative metahoUc fate of aminocarhoxymuconic semialdehyde is decarboxylation, catalyzed hy picolinate carboxylase, leading into the oxidative branch of the pathway, and catabolism via acetyl coenzyme A. There is thus competition between an enzyme-catalyzed reaction that has hyperbolic, saturable kinetics, and a nonenzymic reaction thathas linear, first-order kinetics. 

Fujioka, S., Takatsuto, S. and Yoshida, S. (2002) An early C-22 oxidation branch in the brassinosteroid biosynthetic pathway. Plant Physiol., 130, 930-9. 

Activated ribose phosphate. Write a balanced equation for the synthesis of PRPP from glucose through the oxidative branch of the pentose phosphate pathway. 

Which one of the following compounds is common to both the oxidative branch and the nonoxidative branch of the pentose phosphate pathway ... 

The answer is e. (Murray, pp 219-229. Scrivei pp 1521-1552. Sack, pp 121-138. Wilson, pp 287-317.) The pentose phosphate pathway generates reducing power in the form of NADPH in the oxidative branch of the pathway and synthesizes five-carbon sugars in the nonoxidative branch of the pathway. The pentose phosphate pathway also carries out the interconversion of three-, four-, five-, six-, and seven-carbon sugars in the nonoxidative reactions. The final sugar product of the oxidative branch of the pathway is ribulose-5-phosphate. The first step of the nonoxidative branch of the pathway is the conversion of ribulose-5-phosphate to ribose-5-phosphate or xylulose-5-phosphate in the presence of the enzymes phosphopentose isomerase and phosphopentose epimerase, respectively. Thus ribulose-5-phosphate is a key intermediate that is common to both the oxidative and nonoxidative branches of the pentose phosphate pathway. 

Tsitsilianis et al. recently published [245] preliminary results on the micelliza-tion behavior of anionically synthesized amphiphilic heteroarm star copolymers with polystyrene and poly(ethylene oxide) branches in THF and water. The former solvent is not very selective for one of the segments whereas the latter is strongly selective for PEO. The apparent molecular weights found for the micelles in THF were two orders of magnitude larger than the ones measured for the unimers. By increasing concentration an increase in the depolarization ratio was observed supporting the conclusion that multimolecular micelles are formed by this kind of miktoarm star copolymer. 

Only the nonoxidative branch of the pathway is significantly active when much more ribose 5-phosphate than NADPH needs to be synthesized. Under these conditions, fructose 6-phosphate and glyceraldehyde 3-phosphate (formed by the glycolytic pathway) are converted into ribose 5-phosphate without the formation of NADPH. Alternatively, ribose 5-phosphate formed by the oxidative branch can be converted into pyruvate through fructose 6-phosphate and glyceraldehyde 3-phosphate. In this mode, ATP and NADPH are generated, and five... 

On the other hand, the shape of the current-potential curve is different in the oxidation branch because metallic copper is not concerned by any mass transport phenomenon, since copper is always present at the interface. The zone where the current undergoes large variations is close to the open-circuit potential, which is, in this case, equal to the equilibrium potential of the system. The latter, which can be calculated using the Nernst law, is shifted slightly from the standard potential. To give an order of magnitude for a concentration in Cu ions equal to 10" mol L , there is the following ... 

The working point of the whole system, i.e., the (U,I) couple, corresponds to two points (found on the current-potential curve E,I) of each electrode) such that the values of the current are equal in absolute value (see figure 2.35, dotted vertical lines). Operating such an electrochemical system involves having a point in the oxidation branch and a point in the reduction branch at two different electrodes. Moreover, if there is a difference between the surfaces of the two electrodes, care must be taken to consider the equality of the absolute current values and not that of the current densities . ... 

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