Triiodide reduction by cellobiose:quinone oxidoreductase of Phanerochaete chrysosporium.

Cellobiose:quinone oxidoreductase (CBQase) in the presence of cellobiose inhibits peroxidase-catalyzed oxidation of iodide to triiodide (I3). This inhibition is due to the two-electron reduction of I3- by CBQase. The apparent Km of I3- for this reaction is 120 microM and the specific activity is 57 mumol.min-1.mg-1. A proposed mechanism for I3- reduction by CBQase involves initial reduction of the flavin moiety by cellobiose to produce a dihydroflavin. This is followed by the substitution of one of the iodine atoms of I3- at the C(4a)-position of dihydroflavin to generate C(4a)-iododihydroflavin and two iodide ions. The C(4a)-iododihydroflavin eliminates HI to regenerate the oxidized CBQase.