Carboxylic acid reductases

He A, T Li, L Daniels, I Fotheringham, JPN Rosazza (2004) Nocardia sp. carboxylic acid reductase cloning, expression, and characterization of a new aldehyde oxidoreductase family. Appl Environ Microbiol 70 1874-1881. 

White H, R Feicht, C Huber, F Lottspeich, H Simon (1991) Purification and some properties of the tungsten-containing carboxylic acid reductase from Clostridium formicoaceticum. Biol Chem Hoppe-Seyler 372 999-1005. 

The carboxylic acid reductase in acetogenic Clostridia such as Clostridium thermoaceti-cum (White et al. 1989 Strobl et al. 1992). 

White H, G Strobl, R Feicht, H Simon (1989) Carboxylic acid reductase a new tungsten enzyme catalyses the reduction of non-activated carboxylic acids to aldehydes. Eur J Biochem 184 89-96. 

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. 

Reduction of Carboxylic Acids by Carboxylic Acid Reductase 297 Whole-cell Carboxylic Acid Reduction... 

Clostridium peifringens ferredoxin, 38 261 Clostridium thermoaceticum, 32 326 carboxylic acid reductase, 40 73 CO dehydrogenase, 38 362 formate dehydrogenase, 40 71-72 CISCN, 33 81... 

The aldehyde ferredoxin oxidoreductase from the hyperthermophile Pyrococcus furiosus was the first molybdopterin-dependent enzyme for which a three-dimensional structure became available.683,684 The tungstoenzyme resembles that of the related molybdo-enzyme (Fig. 16-31). A similar ferredoxin-dependent enzyme reduces glyceraldehyde-3-phosphate.685 Another member of the tungstoenzyme aldehyde oxidoreductase family is carboxylic acid reductase, an enzyme found in certain acetogenic clostridia. It is able to use reduced ferredoxin to convert unactivated carboxylic acids into aldehydes, even though E° for the acetaldehyde/acetate couple is -0.58 V.686... 

Carboxylic acid reductase Bacterial aP, a3p3y (MPT)W(0)f Unknown Fe2S2, 2 FAD 267... 

Although molybdenum and tungsten enzymes carry the name of a single substrate, they are often not as selective as this nomenclature suggests. Many of the enzymes process more than one substrate, both in vivo and in vitro. Several enzymes can function as both oxidases and reductases, for example, xanthine oxidases not only oxidize purines but can deoxygenate amine N-oxides [82]. There are also sets of enzymes that catalyze the same reaction but in opposite directions. These enzymes include aldehyde and formate oxidases/carboxylic acid reductase [31,75] and nitrate reductase/nitrite oxidase [83-87]. These complementary enzymes have considerable sequence homology, and the direction of the preferred catalytic reaction depends on the electrochemical reduction potentials of the redox partners that have evolved to couple the reactions to cellular redox systems and metabolic requirements. 

Another tungstoen2yme contained in acetogens is carboxylic acid reductase (CAR), which catalyzes the reduction of carboxylic acids to the corresponding aldehyde ... 

FDH = Formate dehydrogenase CAR = Carboxylic acid reductase FMDH = Formylmethanofuran dehydrogenase MFR = Methanofuran AOR = Aldehyde ferredoxin oxi-doreductase MPT = Molybdopterin Fd x = Oxidized ferredoxin Fdred = Reduced ferredoxin FOR = Formaldehyde ferredoxin oxidoreductase EXAFS = X-ray absorption edge fine structure kDa = Kilodaltons EPR = Electron paramagnetic resonance. 

At the beginning of 2014, Evolva and IFF announced entering the preproduction phase of natural vanillin by a new de novo process starting from glucose [199] in Schizosaccharomyces pombe, andS. cerevisiae. The engineered pathways involve the incorporation of 3-dehydroshikimate dehydratase from the dung mold Podospora pauciseta, an aromatic carboxylic acid reductase (ACAR) from... 

The acetone powder extracts also contained an enzyme that reduced hydroxyglutamic semialdehyde to hydroxyproline, with DPNH serving as the electron donor 177c). It appears that this enzyme is the same as A -pyrroline-5-carboxylic acid reductase 177a-d). 

The reduction of carboxylic acids to aldehydes is of preparative interest and a number of microbial carboxylic acid reductases (CARs) (aldehyde oxidoreductases) have been found since the discovery of the tungsten-containing CAR that reduced nonactivated carboxylic acids to the corresponding aldehydes with no further reduction of the aldehydes to alcohols [83]. The reduction of vanillic add to the aldehyde vanillin has been achieved in vitro with the CAR from Nocardia sp. [84] and as part of a de novo biosynthesis in yeast [85]. A CAR from Mycobacterium marinum has been discovered that can convert a wide range of aliphatic fatty acids (C6-C18) into corresponding aldehydes [86]. 

Akhtara, M.K., Turner, N.J., and Jones, P, R. (2013) Carboxylic acid reductase is a versatile enzyme for the conversion of fatty acids into fuels and chemical commodities, Proc, Natl. Acad. Sci. USA, 110, 87-92,... 

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