Degradation of p-toluic acid (p-toluenecarboxylic acid) and p-toluenesulphonic acid via oxygenation of the methyl sidechain is initiated by the same set of enzymes in Comamonas testosteroni T-2

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Summary: Comamonas testosteroni T-2 utilizes p-toluate (TC, 4-toluenecarboxylate) as sole source of carbon and energy for growth. Cells grown in TC-salts medium oxygenated terephthalate (PcB, 4-carboxybenzoate) and contained protocatechuate 4,5-dioxygenase but no detectable (methyl)catechol dioxygenase. The intermediates 4-carboxybenzyl alcohol (COL), 4-carboxybenzaldehyde (CYD) and PcB were detected during the metabolism of TC. A TC methyl-monooxygenase system, a COL dehydrogenase and a CYD dehydrogenase were detected, analogous to the known degradative pathway and enzymes for 4-toluenesulphonate (TS) to 4-sulphobenzoate (PSB) (Locher et al., Journal of General Microbiology 135, 1969-1978, 1989). Genetic evidence indicated that the steps from TS to PSB and from TC to PcB were catalysed by the same enzymes. This hypothesis was substantiated by purifying or separating the appropriate enzymes from cells grown in TS-salts and TC-salts media. The behaviour of pairs of enzymes was effectively identical in all chromatographic and catalytic properties that were compared. The data support the existence of a novel pathway for the degradation of TC, with the same initial pathway enzymes being used to metabolize TS.