Hydroquinone degradation via reductive dehydroxylation of gentisyl-CoA by a strictly anaerobic fermenting bacterium

Anaerobic degradation of hydroquinone was studied with the fermenting bacterium strain HQGö1. The rate of hydroquinone degradation by dense cell suspensions was dramatically accelerated by addition of NaHCO₃. During fermentation of hydroquinone in the presence of ¹⁴C-Na₂CO₃ benzoate was formed as a labelled product, indicating an initial ortho-carboxylation of hydroquinone to gentisate. Gentisate was activated to the corresponding CoA-ester in a CoA ligase reaction at a specific activity of 0.15 mol x min^–1 x mg protein^–1. Gentisyl-CoA was reduced to benzoyl-CoA with reduced methyl viologen as electron donor by simultaneous reductive elimination of both the ortho and meta hydroxyl group. The specific activity of this novel gentisyl-CoA reductase was 17 nmol x min^–1 x mg protein^–1. Further degradation to acetate was catalyzed by enzymes which occur also in other bacteria degrading aromatic compounds via benzoyl-CoA.