Evidence that cellobiose:quinone oxidoreductase from Phanerochaete chrysosporium is a breakdown product of cellobiose oxidase.

Phanerochaete chrysosporium releases two enzymes that oxidize cellobiose and higher cellodextrins: the flavohaemoprotein cellobiose oxidase and the flavoprotein cellobiose:quinone oxidoreductase (CBQase). Partial digestion of these enzymes with Staphylococcal V8 proteinase or cyanogen bromide yielded many identical bands on SDS-polyacrylamide gels. A polyclonal antibody to either purified protein gave cross-reaction. The purification procedure also yielded a haem protein that ran on dodecyl sulphate gels at Mr 31,000, as compared with 91,000 for cellobiose oxidase and 63,000 for CBQase. The 31 kDa haem protein cross-reacted with polyclonal antibody to cellobiose oxidase, but not with antibody to CBQase. Sulphite bleached the flavin of cellobiose oxidase, but gave no reaction with the 31 kDa haem protein, suggesting an absence of flavin. It is proposed that CBQase and the 31 kDa haem protein are formed from cellobiose oxidase by proteolytic cleavage.