SUGAR OXIDOREDUCTASES AND VERATRYL ALCOHOL OXIDASE AS RELATED TO LIGNIN DEGRADATION

Properties of cellobiose:quinone oxidoreductase (CBQ), cellobiose dehy drogenase (CDH), glyoxal oxidase (GLOX), glucose oxidases and veratryl alcohol oxidase (VAO) are reviewed. There is strong evidence that CDH reduces quinones, phenoxy and cation radicals. Glucose oxidases (gluc ose 1-oxidase and pyranose 2-oxidase) and VAO have been less investiga ted but evidence for reduction of the above compounds is accumulating. Pyranose oxidase, glyoxal oxidase and VAO are very important for hydr ogen peroxide production by white-rot fungi. CDH is only produced on c ellulose or on wood, whereas pyranose oxidase and VAO are produced bot h on wood and on rich glucose media suggesting that the lignin degradi ng white-rot fungi may use different quinone and radical reducing enzy mes to regulate lignin polymerization/depolymerization depending on th e substrate and cultivation conditions. Intracellular quinone reductas es are also produced. Whether brown-rot fungi in general produce CBQ/C DH or VAO is not clear. The Fe(III) reducing ability of both CDH and c ertain phenolate compounds agree with the rapid depolymerization of ce llulose by brown-rot fungi. The interaction of Fe(III) reduction with the hydrogen peroxide producing system in white-rot and brown-rot fung i requires more investigation. (C) 1997 Elsevier Science B.V.