Mandelate pathway

Hegeman GD (1966) Synthesis of the enzymes of the mandelate pathway by Pseudomonas putida I synthesis of enzymes of the wild type. J Bacteriol 91 1140-1154. 

Tsou AY, SC Ransom, JA Gerlt, DD Buechter, PC Babbitt, GL Kenyon (1990) Mandelate pathway of Pseudomonas putida sequence relationships involving mandelate racemase, (5)-mandelate dehydrogenase, and benzoylformate decarboxylase and expression of benzoylformate decarboxylase in Escherichia coli. Biochemistry 29 9856-9862. 

Rosenberg S (1971) Regulation of the mandelate pathway in Pseudomonas aeruginosa. J Bacterial 108 1257-1269. 

The mandelate pathway in Pseudomonas putida involves successive oxidation to benzoyl formate and benzoate, which is further metabolized via catechol and the 3-ketoadipate pathway (Figure 8.35a) (Hegeman 1966). Both enantiomers of mandelate were degraded through the activity of a mandelate racemase (Hegeman 1966), and the racemase (mdlA) is encoded in an operon that includes the next two enzymes in the pathway—5-mandel-ate dehydrogenase (mdlB) and benzoylformate decarboxylase (mdlC) (Tsou et al. 1990). 

Scheme 2.2.1.1 Mandelate pathway benzoylformate decarboxylase (BFD), encoded by the gene md/C, catalyzes the conversion of benzoylformate 3 to benzaldehyde 4 and carbon dioxide.

Another enzyme of the mandelate pathway of degradation of aromatic rings (Fig. 25-8) is the cis,cis-muconate lactonizing enzyme which catalyzes the reaction of Eq. 13-23. It has a three-dimensional struc-... 

Most known thiamin diphosphate-dependent reactions (Table 14-2) can be derived from the five halfreactions, a through e, shown in Fig. 14-3. Each halfreaction is an a cleavage which leads to a thiamin- bound enamine (center, Fig. 14-3) The decarboxylation of an a-oxo acid to an aldehyde is represented by step b followed by a in reverse. The most studied enzyme catalyzing a reaction of this type is yeast pyruvate decarboxylase, an enzyme essential to alcoholic fermentation (Fig. 10-3). There are two 250-kDa isoenzyme forms, one an a4 tetramer and one with an ( P)2 quaternary structure. The isolation of ohydroxyethylthiamin diphosphate from reaction mixtures of this enzyme with pyruvate52 provided important verification of the mechanisms of Eqs. 14-14,14-15. Other decarboxylases produce aldehydes in specialized metabolic pathways indolepyruvate decarboxylase126 in the biosynthesis of the plant hormone indoIe-3-acetate and ben-zoylformate decarboxylase in the mandelate pathway of bacterial metabolism (Chapter 25).1243/127... 

After comparison of DNA sequences of an open reading frame (orf) of the mandelate pathway with databases it was found that there exists sequence similarity of an otherwise unannotated piece of sequence with some amide hydrolases. It is suspected that this DNA sequence piece codes for a mandelate amidase which catalyzes hydrolysis of mandelamide into mandelate and ammonium ion. This hypothesis recently was borne out and the mandelamide hydrolase found (MacLeish, 2003). 

Classic studies were devoted to the regulation of the enzymes for conversion of catechol and protocatechuate to (l-ketoadipate by Pseudomonas putida (Om-ston 1966), the [f-ketoadipate pathway in Moraxella calcoacetica (Canovas and Stanier 1967), and the mandelate pathway in P. aeruginosa (Rosenberg 1971). All of these organisms cleave the catechol by intradiol fission catalyzed by a... 

The second representative of the class of thiamine pyrophosphate-dependent nonoxidative a-keto acid decarboxylases is phenylglyoxylate decarboxylase (benzoylformate decarboxylase EC 4.1.1.7). This enzyme participates in the catabolism of aromatic compounds as part of mandelate pathway in different Pseudomonas and Acinetobacter species, normally converting benzoylformate to benzaldehyde [81-83]. This pathway is induced by mandelic acid [84]. 

Benzoylformate decarboxylase from Pseudomonas and Acinetobacter species, also an a-keto acid decarboxylase, has higher substrate specificity than pyruvate decarboxylase. Cells of these species grown in media inducing the mandelate pathway enzymes can convert benzoylformate and acetaldehyde to optically active 2-hydroxypropiophenone. Benzaldehyde is produced in this biotransformation reaction, as it is the normal product of benzoylformate decarboxylase. Some benzyl alcohol is also produced, in this case probably by reduction of benzaldehyde by cell oxidoreductases. In the case of P. putida the (S) enantiomer form of 2-hydrox) ropiophenone was produced, with an e.e. of 91-92%. The same product produced by A. calcoaceticus had an e.e. of 98%. An optimal volumetric production of 2-hydroxypropiophenone of 6.95 g per L per h was reported. 

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