NADH/NADPH

Ketoreductases catalyze the reversible reduction of ketones and oxidation of alcohols using cofactor NADH/NADPH as the reductant or NAD + /NADP+ as oxidant. Alcohol oxidases catalyze the oxidation of alcohols with dioxygen as the oxidant. Both categories of enzymes belong to the oxidoreductase family. In this chapter, the recent advances in the synthetic application of these two categories of enzymes are described. 

At least two enzymes compete for acetyl-CoA - the citrate synthase and 3-ke-tothiolase. The affinities of these enzymes differ for acetyl-CoA (Table l),and at low concentrations of it the citrate synthase reaction tends to dominate, provided that the concentration of 2/H/ is not inhibiting. The fine regulation of the citrate synthases of various poly(3HB) accumulating bacteria has been studied [ 14, 47, 48]. They appear to be controlled by cellular energy status indicators (ATP, NADH, NADPH) and/or intermediates of the TCA cycle. The 3-ketothio-lase has also been investigated [10-14,49, 50]. This enzyme is, above all, inhibited by CoASH [10,14,49]. This important feature will be further considered below. 

Reduced flavins (FADH2, FMNH2, and riboflavin) generated by flavin-dependent reductases have been hypothesized to reduce azo dyes in a nonspecific chemical reaction, and flavin reductases have been revealed to be indeed anaerobic azoreductases. Other reduced enzyme cofactors, for example, NADH, NADH, NADPH, and an NADPH-generating system, have also been reported to reduce azo dyes. Except for enzyme cofactors, different artificial redox mediating compounds, especially such as quinines, are important redox mediators of azo dye anaerobic reduction (Table 1). 

It has been proposed [91] that nitric dioxide radical formation during the oxidation of nitrite by HRP or lactoperoxidase (LPO) can contribute to tyrosine nitration and be involved in cell and tissue injuries. This proposal was supported in the later work [92] where it has been shown that N02 formed in peroxide-catalyzed reactions is able to enter cells and induce tyrosyl nitration. Reszka et al. [93] demonstrated that N02 mediated the oxidation of biological electron donors and antioxidants (NADH, NADPH, cysteine, glutathione, ascorbate, and Trolox C) catalyzed by lactoperoxidase in the presence of nitrite. 

NADH/NADPH SURFACE FLUORESCENCE IN LIVING TISSUES... 

Surface fluorescence of NADH/NADPH can be recorded continuously with a DC fluorimeter and correlated with changes in experimental conditions. A mercury arc lamp (with a 340-375 nm filter in front) is used as a hght source for fluorescence excitation. The fluorescence response of reduced NADH/NADPH was measured at 450-510 nm. The DC fluorimeter and the Hg arc lamp are connected to the kidney by a trifurcated fiber optics light guide. NADH/NADPH fluorescence emission can be corrected for changes in tissue opacity by a 1 1 subtraction of reflectance changes at 340-375 nm from the fluorescence. To determine NADH/NADPH redox state of the total surface area of kidney cortex and to evaluate whether certain areas were insufficiently perfused, fluorescence photographs of the total surface area were taken. The study demonstrated that the surface fluorescence method is simple and provides specific information about the mitochondrial oxidation-reduction state. 

Mitochondrial oxidation-reduction state, NADH/NADPH SURFACE FLUORESCENCE IN LIVING TISSUES MITOGEN-ACTIVATED PROTEIN KINASE... 

DT diaphorase Dicoumarol-sensitive NADH/NADPH dye reductase, ductule small duct, dyspnea labored breathing. 

Catabolism is the degradative phase of metabolism in which organic nutrient molecules (carbohydrates, fats, and proteins) are converted into smaller, simpler end products (such as lactic acid, C02, NH3). Catabolic pathways release energy, some of which is conserved in the formation of ATP and reduced electron carriers (NADH, NADPH, and FADH2) the rest is lost as heat. In anabolism, also called biosynthesis, small, simple precursors are built up into larger and more complex... 

FIGURE 3 Energy relationships between catabolic and anabolic pathways Catabolic pathways deliver chemical energy in the form of ATP, NADH, NADPH, and FADH2. These energy carriers are used in anabolic pathways to convert small precursor moleculesinto cell macromolecules. 

Azumi H, Inoue N, Takeshita S, Rikitake Y, Kawashima S, Hayashi Y, Itoh H, Yokoyama M. 1999. Expression of NADH/NADPH oxidase p22phox in human coronary arteries. Circulation 100 1494-1498. 

Enantioselective oxidation of racemic alcohols as well as reduction of racemic ketones and aldehydes have been widely applied to obtain optically active alcohols.25 27 The enzymes catalyzing these reactions are alcohol dehydrogenase, oxidases, and reductases etc. Coenzymes (NADH, NADPH, flavine etc) are usually necessary for theses enzymes. For example, for the oxidation of alcohols, NAD(P)+ are used. The hydride removed from the substrate is transferred to the coenzyme bound in the enzyme, as shown in Figure 24. There are four stereochemical patterns, but only three types of the enzymes are known. 

Rajagopalan, S., Kurz, S., Munzel, T., et al. 1996. Angiotensin II-mediated hypertension in the rat increases vascular superoxide production via membrane NADH/NADPH oxidase activation. Contribution to alterations of vasomotor tone. J Clin Invest 97 1916-1923. 

Zafari, A. M., Ushio-Fukai, M., Minieri, C. A., et al. 1999. Arachidonic acid metabolites mediate angiotensin Il-induced NADH/NADPH oxidase activity and hypertrophy in vascular smooth muscle cells. Antioxidants Redox Signal 1 167-179. 

Nicotinamide nucleotide (NAD, NADP, NADH, NADPH) levels (Table 4.6) have been measured only in one cestode, H. diminuta (42), which probably reflects the difficulty of carrying out such an analysis. In this... 

---