We recently demonstrated the presence of a quinone detoxification pathway present in Firmicutes. It is based on two enzyme activities, namely a hydroquinone dioxygenase, YaiA, described here, and a hydroquinone reductase, YaiB, described in a separate protocol. In Lactococcus lactis (L. lactis), these enzymes are encoded by the yahCD-yaiAB operon. The operon is induced by copper to prevent the synergistic toxicity of quinones and copper. The hydroquinone dioxygenase, YaiA, converts hydroquinones to 4-hydroxymuconic semialdehyde, using molecular oxygen as oxidant according to the reaction: hydroquinone + O2 → 4-hydroxymuconic semialdehyde + H+ We here describe two methods for measurements for hydroquinone dioxygenase activity, based on oxygen consumption measured with an oxygen electrode and the spectrophotometric detection of 4-hydroxymuconic semialdehyde. Both assays are conducted with crude cell extracts.
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