4-Hydroxybenzoylformate decarboxylase enzymes from Rhodococcus jostii RHA1 and Pseudomonas fluorescens Pf-5: Characterisation and involvement in bacterial lignin degradation.

Genes encoding thiamine diphosphate-dependent benzoylformate decarboxylase (BFDC) enzymes are found in a gene cluster implicated in lignin degradation in Rhodococcus jostii RHA1, and in a related gene cluster in Pseudomonas fluorescens Pf-5. In order to study their function, the recombinant enzymes were expressed and characterised kinetically. The article describes methods for continuous UV-visible assay and HPLC assay of BFDC, and determination of kinetic constants. Carboligase activity with vanillin and acetaldehyde as substrates was also studied for these enzymes. Two hypotheses for possible degradation pathways involving BFDC were studied, and evidence obtained in favour of a pathway proceeding via 4-hydroxy-3-methoxybenzoylformic acid, for degradation of aryl C2 fragments arising from lignin degradation.