We recently demonstrated the presence of a quinone detoxification pathway present in Firmicutes. It is based on two enzyme activities, namely a quinone reductase, YaiB, described here, and a hydroquinone dioxygenase, YaiA, 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 quinone reductase, YaiB, reduces p-benzoquinone and a range of quinone derivatives to hydroquinone, using NADPH as a reductant, according to the reaction: p-benzoquinone + NADPH + H+ → hydroquinone + NADP+. We here describe the measurement of quinone reductase activity, based on the spectrophotometric measurement of NADPH-oxidation.
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