REDUCTION OF QUINONES AND RADICALS BY A PLASMA-MEMBRANE REDOX SYSTEM OF PHANEROCHAETE-CHRYSOSPORIUM

Quinones which are produced during the mineralization of lignin and xe nobiotics by the white rot fungus Phanerochaete chrysosporium were red uced by a plasma membrane redox system of the fungus. Both intracellul ar enzymes and the plasma membrane redox system were able to reduce 1, l-benzoquinone. However, no quinone reductase activity was observed wi th the extracellular culture fluid. The intracellular reductase activi ty had a pH optimum between 6.0 and 7.0 and a K-m of 150 mu M. Reducti on of 1,4-benzoquinone by the plasma membrane redox system had a pH op timum between 7.5 and 8.5 and exhibited saturation kinetics (K-m = 11 mu M, V-max = 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 ca n be generated by the lignin peroxidases were also reduced by the plas ma membrane redox system. Reduction of the ARTS cation radical also to tally inhibited quinone reduction until the radical was completely red uced. Finally, quinone reduction rates were identical after the reduct ion 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. (C) 1995 Academic Press, Inc.