Reductases replacement

A second system for fatty acid elongation exists in the mitosol, probably for provision of long fatty acids for mitochondrial structure. This system uses most of the same activities of 9-oxidation, but an NADPH dependent Enoyl-CoA reductase replaces the FAD dependent dehydrogenase. 

Recombinant Saccharomyees cerevisiae, able to ferment the pentoses D-xylose and L-arabinose, was modified for improved fermentation rates and yields. Pentose fermentation is relevant when low cost raw materials such as plant hydrolysates are fermented to ethanol. The two most widespread pentose sugars in our biosphere are D-xylose and L-arabinose. S. cerevisiae is unable to ferment pentoses but has been engineered to do so however rates and yields are low. The imbalance of redox cofactors (excess NADP and NADH are produced) is considered a major limiting factor. For the L-arabinose fermentation we identified an NADH-dependent L-xylulose reductase replacing the previously known NADPH-dependent enzyme. For D-xylose fermentation we introduced an NADP-dependent glyceraldehyde 3-phospate dehydrogenase to regenerate NADPH. 

The sulfa dmgs are stiH important as antimicrobials, although they have been replaced in many systemic infections by the natural and semisynthetic antibiotics. They are of great value in third world countries where problems of storage and lack of medical personnel make appropriate use of antibiotics difficult. They are especially useful in urinary tract infections, particularly the combination of sulfamethoxazole with trimethoprim. Their effectiveness has been enhanced by co-adniinistration with dihydrofolate reductase inhibitors, and the combination of sulfamethoxazole with trimethoprim is of value in treatment of a number of specific microbial infections. The introduction of this combination (cotrimoxazole) in the late 1960s (1973 in the United States) resulted in increased use of sulfonamides. 

HMG CoA-Reductase HMG-CoA-Reductase Inhibitors Homologous Desensitization Homologous Proteins Homologous Recombination Homology Modeling Hormonal Contraceptives Hormone Replacement Therapy (HRT)... 

There are other substrates for the E. coli Met(0) peptide reductase, one of which is Met(0)-a-l-PI. The native protein is the major serum elastase inhibitor that functions by forming a binary complex with elastase which inhibits its activity. Met(0)-a-l-PI, on the other hand, which can be formed by treatment of the protein with TV-chlorosuccinimide, cannot form a complex with elastase and therefore is not able to inhibit elastase activity117,118. Table 6 shows, however, that when Met(0)-a-l-PI is incubated in the presence of Met(0)-peptide reductase and dithiothreitol the protein regains its ability to form a complex with elastase and inhibit elastase activity119. Similar to results found with Met(0)-L12 reduced thioredoxin could replace the dithiothreitol as reductant in the enzymatic reaction. 

Sulfate reducers can use a wide range of terminal electron acceptors, and sulfate can be replaced by nitrate as a respiratory substrate. Molybdenum-containing enzymes have been discovered in SRB (also see later discussion) and, in particular, D. desulfuricans, grown in the presence of nitrate, generates a complex enzymatic system containing the following molybdenum enzymes (a) aldehyde oxidoreduc-tase (AOR), which reduces adehydes to carboxylic acids (b) formate dehydrogenase (FDH), which oxidizes formate to CO2 and (c) nitrate reductase (the first isolated from a SRB), which completes the enzy-... 

Yamazaki, H., Ueng, Y.F., Shimada, T. and Guengerich, F.P. (1995) Roles of divalent metal ions in oxidations catalyzed by recombinant cytochrome P450 3A4 and replacement of NADPH-cytochrome P450 reductase with other flavoproteins, ferredoxin, and oxygen surrogates. Biochemistry, 34, 8380—8389. 

These findings lead to (he conclusion that the reduction of MHb by its reductase requires a natural cofactor, which is abolished during the purification procedure and can be replaced by methylene blue (G5, H22, H23, K8, K14). Since methylene blue and the other effective dyes are redox intermediates, it is obvious that the postulated cofactor interacts in the electron transport sequence of the MHbR reaction (H23). This is confirmed by the finding that oxygen and cytochrome c serve as well as terminal electron acceptor as does MHb (H22, H23, K14). Nevertheless, it had been possible to separate a cytochrome c reductase from MHbR in yeast extracts (A6). 

If cyclohexanecarboxaldehyde is incubated with CYP2B4, NADPH, and cytochrome P450 reductase, the aldehyde-cyclohexyl ring carbon-carbon bond is cleaved generating cyclohexene and formic acid (150) (Fig. 4.81). The reaction is supported if hydrogen peroxide replaces NADPH and cytochrome P450 reductase but is not supported if other oxidants at the same oxidation equivalent as peroxide but bypass the peroxy form of P450 such as iodosobenzene, m-chloroperbenzoic acid, or cumyl hydroperoxide are used. These... 

The biocatalytic reduction of carboxylic acids to their respective aldehydes or alcohols is a relatively new biocatalytic process with the potential to replace conventional chemical processes that use toxic metal catalysts and noxious reagents. An enzyme known as carboxylic acid reductase (Car) from Nocardia sp. NRRL 5646 was cloned into Escherichia coli BL21(DE3). This E. coli based biocatalyst grows faster, expresses Car, and produces fewer side products than Nocardia. Although the enzyme itself can be used in small-scale reactions, whole E. coli cells containing Car and the natural cofactors ATP and NADPH, are easily used to reduce a wide range of carboxylic acids, conceivably at any scale. The biocatalytic reduction of vanillic acid to the commercially valuable product vanillin is used to illustrate the ease and efficiency of the recombinant Car E. coli reduction system." A comprehensive overview is given in Reference 6, and experimental details below are taken primarily from Reference 7. 

Scheme 25 Example of thiolation (T) domains in type I NRPS. Nostocyclopeptide is shown as a representative nonribosomal peptide. Seven T domains are found in the seven modules, each depicted in a different color, responsible for the incorporation of the seven amino acid building block constituents of nostocyclopeptide. A reductase (R) domain replaces the more common TE domain for the formation of the unusual imine functionality.

Several characterized NRPSs utilize alternative methods for chain termination. In some synthetases, the TE domain of the final module is replaced by an NAD(P)H-dependent reductase domain. Reduction of a peptidyl-S-PCP substrate through a two-electron reaction leads to the formation of a transient aldehyde, which is subsequently converted into a cyclic imine or hemiaminal through intramolecular cyclization. This two-electron reaction is utilized in the biosynthesis of nostocyclopeptides, the saframycins, ° and anthramycin. Alternatively, a four-electron reduction to the primary alcohol is observed in the biosynthesis of mycobacterial peptidolipids, linear gramicidin," " the myxalamides, lyngbyatoxin, " and myxochelin A 75,76 alternative four-electron reduction pathway involving aldehyde formation, transamination, and reduction to a primary amine occurs in the biosynthesis of myxochelin B. ... 

Formation of biliverdin or Fe(III)-biliverdin may be dependent on the nature of the reductase, since replacement of the reductase with ascorbate in the HO-catalyzed reaction leads to formation of Fe(III)-biliverdin 282). 

This enzyme [EC 1.8.4.5], also known as methionine S-oxide reductase, catalyzes the reaction of L-methionine with oxidized thioredoxin to produce L-methionine S-oxide and reduced thioredoxin. Dithiothreitol can substitute for reduced thioredoxin in the reverse reaction. In addition, other methyl sulfoxides can replace methionine sulfoxide in the reverse reaction. 

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