Aryl-aldehyde dehydrogenase

Nicotinamide Adenine Dinucleotide phosphate (NADP+) Glutamate dehydrogenase, Alcohol dehydrogenase, Aryl-aldehyde dehydrogenase... 

Vanillin is the second largest food additive used each year. As a consequence of limited natural sources of this ubiquitous flavor and fragrance, the bulk of commercial vanillin is synthesized from phenol (19). A two-step synthesis of vanillin from glucose via DHS intermediacy was recently reported (Figure 3) (17). DHS dehydratase-catalyzed conversion of DHS into PCA is followed by formation of the methyl ether, catalyzed by catechol-O-methyltransferase, an enzyme not native to E. coli but for which the gene (comt) has been cloned from rat liver (20). In a separate step, incubation of the resulting vanillic acid with aryl-aldehyde dehydrogenase (21) affords vanillin. 

Figure 3. Synthesis of vanillin from DHS. Enzymes (a) DHS dehydratase (aroZ) (b) catechol-O-methyltransferase (comt) (c) aryl-aldehyde dehydrogenase (d) glucose 6-phosphate dehydrogenase, glucose 6-phosphate.

Aryl-aldehyde dehydrogenase was purified from Neurospora crassa to remove a dehydrogenase that reduces vanillin to vanillyl alcohol 23). Vanillic acid, isovanillic acid, and PCA were extracted from a fermentation broth with ethyl acetate. Reprecipitation of the isolated products increased the vanillic acid PCA ratio from 1 2 to 2.5 1 (mol/mol). Incubation of the resulting mixture with aryl aldehyde dehydrogenase, NADP, and ATP for 7 h at 30 C resulted in a 92% reduction of vanillic acid to vanillin but only a 33% reduction of PCA to protocatechualdehyde. Vanillin was extracted from the reaction with CH2CI2, affording a product with 10 mol % isovanillin as the only detected contaminant. Based on the concentration of vanillic acid in the fermentation broth, reduction of vanillic acid through purification of vanillin proceeded in 66% overall yield. 

OH De novo produced vanillic acid by aryl aldehyde dehydrogenase from Neurospora crassa) Saccharomyces 45 [89]... 

The second category of aldehyde dehydrogenases are efficient catalysts of the oxidation of both aryl and alkyl aldehydes to the corresponding carboxylic acids. The most well known and common of such reactions is the oxidation of acetaldehyde, derived from alcohol, to acetic acid. 

Cytochrome P450 Alcohol dehydrogenase Aldehyde dehydrogenase Aldehyde oxidase Carboxylesterase Aiylesterase Acetylesterase Aryl 4-hydroxylase Aryl sulphatase... 

Bakers yeast is used almost exclusively for reduction, principally of ketones, by a dehydrogenase which usually follows the Prelog-Cram rule. As with chemical reductions, highest enantioselectivity obtains with aromatic aldehydes and aryl methyl ketones. /3-Keto esters arc also reduced with high canantiosclectivity by yeast. Some j8-kcto acids can also be reduced efficiently to (R)-jS-hydroxy acids. 

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