NADH , internal complexes

For example, liver alcohol dehydrogenase was crystallized as the enzyme N AD1 p-bromobenzyl alcohol complex with saturating concentrations of substrates in an equilibrium mixture51b and studied at low resolution. Transient kinetic studies or direct spectroscopic determinations led to the conclusion that the internal equilibrium (E NAD alcohol = E NADH aldehyde) favors the NAD1 alcohol complex.52 Subsequently, the complex was studied at higher resolution, and the basic structural features were confirmed with a... 

In a fifth method (International Reagents Corp., Kokusai-Kobe, Japan), its first reagent contains the detergent cal-ixarene that converts LDL to a soluble complex. Cholesterol esters of HDL-C and VLDL-C are preferentially hydrolyzed by a cholesterol esterase (chromobacterium), cholesterol oxidase, and hydrazine, which divert the accessible cholesterol to cholestenone hydrazone. A second reagent with deoxycholate brealcs up the LDL-calixarene complex, allowing LDL-C to react with the esterase, a dehydrogenase, and P-NAD to yield cholestenone and fi-NADH, the latter measured by a spectrophotometer. 

The electrons provided in the light reaction, however, may also be directly exported from the cells and used to reduce a variety of extracellular substrates. This electron export is effected by surface enzymes (called transplasmamembrane reductases) spanning the plasmamembrane from the inside surface to the outside. They transfer electrons from an internal electron donor [chiefly NADH and NADPH see Crane et al. (1985)] to an external electron acceptor. Direct reduction of extracellular compounds by transplasmamembrane electron transport proteins is prevalent in all cells thus far examined (Fig. 2.2). Although the function of this redox system is still subject to speculation, in phytoplankton it shows considerable activity, relative to other biochemical processes. A host of membrane-impermeable substrates, including ferricyanide, cytochrome c, and copper complexes, are reduced directly at the cells surface by electrons originating from within the cell. In phytoplankton, where the source of electrons is the light reactions of photosynthesis, the other half-redox reaction is the evolution of ()2 from H20. In heterotrophs, the electrons originate in the respiration of reduced substances. 

In the inner mitochondrial membrane there reside many copies of a molecular complex that is a marvel of nanoengineering the FoFiATPase. This consists of an intramembranous channel, the Fq section, that conducts protons across the membrane, and another section of the complex located on the internal side of the inner mitochondrial membrane, FiATPase it phosphorylates ADP with P, to generate ATP. The three-dimensional structure and the molecular mechanism of this incredible ATP generator are discussed further in Sec. 10.11. The mechanism of synthesis of ATP by the FqF, ATPase that is coupled to the flow of electrons from NADH and FADHj along the ETC is called oxidative phosphorylation. 

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