Reduction of Quinones and Radicals by a Plasma Membrane Redox System of Phanerochaete chrysosporium

Quinones which are produced during the mineralization of lignin and xenobiotics by the white rot fungus Phanerochaete chrysosporium were reduced by a plasma membrane redox system of the fungus. Both intracellular enzymes and the plasma membrane redox system were able to reduce 1,l-benzoquinone. However, no quinone reductase activity was observed with the extracellular culture fluid. The intracellular reductase activity had a pH optimum between 6.0 and 7.0 and a Km of 150 μM. Reduction of 1,4-benzoquinone by the plasma membrane redox system had a pH optimum between 7.5 and 8.5 and exhibited saturation kinetics (Km = 11 μM, Vmax = 16 nmol/min/mg mycelia dry weight). Ferricyanide totally inhibited the quinone reduction until the ferricyanide was completely reduced by the membrane. Radicals (chlorpromazine and 2,2′-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS)) that can be generated by the lignin peroxidases were also reduced by the plasma membrane redox system. Reduction of the ABTS cation radical also totally inhibited quinone reduction until the radical was completely reduced. Finally, quinone reduction rates were identical after the reduction of ferricyanide, ABTS cation radical, or quinone, suggesting that the plasma membrane redox system may actually protect the fungus from oxidative damage from free radicals generated by the lignin degrading system.