Reactions of reduced cellobiose oxidase with oxygen. Is cellobiose oxidase primarily an oxidase?

We report rapid-mixing experiments in which cellobiose oxidase, fully reduced with cellobiose, is allowed to react with excess molecular O2. Analysis of the progress curves and their comparison with computer simulations suggests that O2 reacts only with the cytochrome b-type haem and with a rate constant of approx. 0.5 s-1. In steady state the cytochrome b is partially oxidized, whereas the flavin remains largely reduced. This situation may be contrasted with that when dichloroindophenol is substituted for O2. Under these conditions the reactions are rapid (millisecond time range), and the redox centres in the enzyme appear to be oxidized simultaneously.