NADH coenzyme

The NAD -NADH coenzyme system is involved m a large number of biological changes during the enzyme... 

Zincke salts have played an important role in the synthesis of NAD /NADH coenzyme analogs since a 1937 report on the Zincke synthesis of dihydropyridine 7 for use in a redox titration study.The widely utilized nicotinamide-derived Zincke salt 8, first synthesized by Lettre was also used by Shifrin in 1965 for the preparation and study of NAD /NADH analogs. In 1972, Secrist reported using 8 for synthesis of simplified NAD analogs such as 10 for use in spectroscopic studies (Scheme 8.4.4). Subsequent utilization of 8 is discussed later in this article. 

Abnormalities of the respiratoiy chain. These are increasingly identified as the hallmark of mitochondrial diseases or mitochondrial encephalomyopathies [13]. They can be identified on the basis of polarographic studies showing differential impairment in the ability of isolated intact mitochondria to use different substrates. For example, defective respiration with NAD-dependent substrates, such as pyruvate and malate, but normal respiration with FAD-dependent substrates, such as succinate, suggests an isolated defect of complex I (Fig. 42-3). However, defective respiration with both types of substrates in the presence of normal cytochrome c oxidase activity, also termed complex IV, localizes the lesions to complex III (Fig. 42-3). Because frozen muscle is much more commonly available than fresh tissue, electron transport is usually measured through discrete portions of the respiratory chain. Thus, isolated defects of NADH-cytochrome c reductase, or NADH-coenzyme Q (CoQ) reductase suggest a problem within complex I, while a simultaneous defect of NADH and succinate-cytochrome c reductase activities points to a biochemical error in complex III (Fig. 42-3). Isolated defects of complex III can be confirmed by measuring reduced CoQ-cytochrome c reductase activity. 

NADH-coenzyme Q (CoQ) oxidoreductase, transfers electrons stepwise from NADH, through a flavoprotein (containing FMN as cofactor) to a series of iron-sulfur clusters (which will be discussed in Chapter 13) and ultimately to CoQ, a lipid-soluble quinone, which transfers its electrons to Complex III. A If, for the couple NADH/CoQ is 0.36 V, corresponding to a AG° of —69.5 kJ/mol and in the process of electron transfer, protons are exported into the intermembrane space (between the mitochondrial inner and outer membranes). 

Correlations with Hantzsch esters) (70) (77BSB267). This latter type of compound is of interest as an effective model for the NAD/NADH coenzyme system, and this work provides detailed analysis of H and 13C NMR of such compounds. 

NADH coenzyme Q reductase defect (complex I) Succinate coenzyme Q reductase defect (complex II) Coenzyme Q cytochrome C reductase defect (complex III)... 

NADH cytochrome bj Adenylate kinase NADH-coenzyme Q Pyruvate dehydrogenase... 

The NAD -NADH coenzyme system is involved in a large number of biological oxidation-reductions. Another reaction similar to the ethanol-acetaldehyde conversion is the oxidation of lactic acid to pyruvic acid by NAD and the enzyme lactic acid dehydrogenase ... 

A key property of the enzyme, established by x-ray data, is the existence of two protein domains in each monomer that are relatively free to rotate relative to each other. The apo- and holo-enzymes exist in the so-called open form, whereas binding of NADH coenzyme induces rotation of one domain, resulting in the so-called closed form - " (Figures 2.34 and 2.35). Closure brings the catalytic zinc ion into an ideal position to bind the aldehyde substrate in such a way that the reactive CH2 group of the nicotinamide ring of NADH points toward... 

Iron centers undergo cyclic oxidoreduction between ferrous and ferric states, as shown here. Complex I is also called NADH-coenzyme Q reductase because the electrons are used to reduce coenzyme Q. The passage through Complex I can be blocked by the compounds rotenone and amytal and the artificial electron acceptor methylene blue can accept electrons from FMNH2 Figure 15.9. 

See also Electron Transport, NADH, Coenzyme Q, Amytal... 

See also NADH, Coenzyme Q, Inhibitors and Artificial Electron Acceptors... 

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