THE CELLOBIOSE-OXIDIZING ENZYMES CBQ AND CBO AS RELATED TO LIGNIN ANDCELLULOSE DEGRADATION - A REVIEW

In this review properties of cellobiose:quinone oxidoreductase (CBQ) a nd cellobiose oxidase (CbO) are presented and their possible involveme nt in lignin and cellulose degradation is discussed. Although these en zymes are produced by many different fungi, their importance for wood- degrading fungi is the topic here. CBQ is a FAD enzyme, while CbO also contains a heme group of the cytochrome b type. Protease activity is reported to convert CbO to CBQ. During oxidation of cellobiose (emanat ing from cellulose) to cellobiono-1,5-lactone, both enzymes reduce qui nones produced by laccase and peroxidase during lignin degradation to the corresponding phenols. Many phenoxy and cation radicals are also r educed. Quinone reduction is more rapid than oxygen reduction, althoug h oxygen is slowly reduced to superoxide and/OT hydrogen peroxide. Thu s, a more appropriate name for CbO is cellobiose dehydrogenase. CbO al so reduces Fe(III) and together with hydrogen peroxide produced by the enzyme Fenton's reagent may be formed, resulting in hydroxyl radical production. This radical can degrade both lignin and cellulose, possib ly indicating that cellobiose oxidase has a central role in degradatio n of wood by wood-degrading fungi.