Biological Kolbe-Schmitt carboxylation

Possible use of enzymes for the direct carboxylation of organic substrates 

Department of Biomolecular Science, Faculty of Engineering, Gifu University, Yanagido, Gifu, Japan 

Phenol is an important intermediate in the anaerobic degradation of many complex and simple aromatic compounds. Tschech and Fuchs proposed that the carboxylation of phenol to 4-hydroxybenzoate is the first step in the degradation of phenol under denitrifying conditions. However, 4-hydroxybenzoate is not detected in the cultures or cell extracts of the denitrifying Pseudomonas species in the presence of CO2 and phenol, but it is detected if phenol is replaced by phenolphosphate. In contrast, 4-hydroxybenzoate is readily detected as an intermediate of phenol degradation in the iron-reducing bacterium GS-15, and 4-hydroxybenzoate may prove to be a common intermediate in the anaerobic transformation. Thus, in anaerobic degradation of phenolic compounds, it has been postulated that carboxylation reactions may play important roles. 

Zhang et al. isolated Clostridium hydroxybenzoicum containing two inducible 4-hydroxybenzoate decarboxylase and 3,4-dihydroxybenzoate decarboxylase that form phenol and catechol (1,2-dihydroxybenzene), respectively. The organism does not further metabolize phenol and catechol produced by these reactions. The carboxylation activities of the two purified decarboxylases are not 

Pure cultures growing anaerobically with catechol and sulfate were isolated,and the carboxylation of catechol was proposed to be the initial reaction of anaerobic catechol degradation by Desulfobacterium sp. strain Cat2. Zhang and Young proposed that the initial key reaction for anaerobic degradation of naphthalene and phenanthrene was also carboxylation. 

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