GLYOXAL OXIDASE FROM PHANEROCHAETE-CHRYSOSPORIUM IS A NEW RADICAL-COPPER OXIDASE

A free radical-coupled copper complex has been identified as the catal ytic structure in the active site of glyoxal oxidase from Phanerochaet e chrysosporium based on a combination of spectroscopic and biochemica l studies, The native (inactive) enzyme is activated by oxidants leadi ng to the elimination of the cupric EPR signal consistent with formati on of an antiferromagnetically coupled radical-copper complex, Oxidati on also leads to the appearance of a substoichiometric free radical EP R signal with an average g value (g(av) = 2.0055) characteristic of ph enoxyl pi-radicals arising from a minority apoenzyme fraction, Optical absorption, CD, and spectroelectrochemical measurements on the active enzyme reveal complex spectra extending into the near IR and define t he redox potential for radical formation (E(1/2) = 0.64 V versus NHE, pH 7.0), Resonance Raman spectra have identified the signature of a mo dified (cysteinyl-tyrosine) phenoxyl in the vibrational spectra of the active complex, This radical-copper motif has previously been found o nly in galactose oxidase, with which glyoxal oxidase shares many prope rties despite lacking obvious sequence identity, and catalyzing a dist inct reaction, The enzymes thus represent members of a growing class o f free radical metalloenzymes based on the radical-copper catalytic mo tif and appear to represent functional variants that have evolved to d istinct catalytic roles.