An extracellular enzyme from culture filtrates of Sporotrichum (Chrysosporium) thermophile (A.T.C.C. 42 464) after growth on cellulose or cellobiose was shown to oxidize cellobiose to cellobionic acid in vitro. Lactose and cellodextrins were also efficiently oxidized, but the enzyme was not active against most mono- and di-saccharides. Several redox substances could act as electron acceptors, but molecular oxygen, tetrazolium salts and NAD(P) were not reduced. Activity was stimulated up to 2-fold in the presence of 0.05 M-Mg2+. The pH optimum of the enzymic reaction was acidic when the activity was tested with dichlorophenol-indophenol or Methylene Blue, but was neutral to alkaline for 3,5-di-t-butyl-1,2-benzoquinone or phenazine methosulphate as electron acceptors. As the enzyme was formed inductively in parallel with the endocellulase, its possible function in relation to cellulolysis is discussed.
