Cellobiose dehydrogenase (CDH), an extracellular flavocytochrome produced by several wood-degrading fungi, was detected in cultures of the selective delignifier Ceriporiopsis subvermispora when grown on a cellulose-and yeast extract-based liquid medium. CDH amounted to up to 2.5% of total extracellular protein during latter phases of the cultivation and thus suggested an important function for the fungus under the given conditions. The enzyme was purified 44-fold to apparent homogeneity. It was found to be present in two glycoforms of 98 kDa and 87 kDa with carbohydrate contents of 16 and 4%, respectively. The isoelectric point of both glycoforms is around 3.0, differing by 0.1 units, which is the most acidic value so far reported for a CDH. By using degenerated primers of known CDH sequences, one cdh gene was found in the genomic DNA, cloned, and sequenced. Alignment of the 774-amino-acid protein sequence revealed a high similarity to CDH from other white rot fungi. One notable difference was found in the longer interdomain peptide linker, which might affect the interdomain electron transfer at higher temperatures. The preferred substrate of C. subvermispora CDH is cellobiose, while glucose conversion is strongly discriminated by a 155,000-fold-lower catalytic efficiency. This is a typical feature of a basidiomycete CDH, as are the acidic pH optima for all tested electron acceptors in the range from 2.5 to 4.5.White rot fungi are the most efficient lignocellulose degraders in our ecosystem, and several species, e.g., Phanerochaete chrysosporium, Trametes versicolor, and Ceriporiopsis subvermispora, have been studied in great detail as model organisms for this complex process. The ability to degrade phenolic and nonphenolic lignin structures in wood has made these strains attractive for biotechnological applications mainly in the pulp and paper industry, where C. subvermispora exhibits a substantial advantage over P. chrysosporium and T. versicolor through its ability for selective removal of a large fraction of lignin without attacking the valuable cellulose (16, 38). The lignindegrading system of these fungi is composed of extracellular enzymes together with low-molecular-mass cofactors (21, 46). Typically found ligninolytic enzymes are lignin peroxidase, manganese peroxidase (MnP), and laccase. The secretion pattern of these enzymes varies greatly in white rot fungi (22) and is influenced by culture conditions and medium composition. Whereas P. chrysoporium secretes high lignin and manganese peroxidase activities but no laccase activity (32, 33), C. subvermispora produces several MnP and laccase isoforms but no lignin peroxidase. T. versicolor is the only one of these model organisms known so far to express all three of these ligninolytic enzymes efficiently (5). Together with the cellulolytic enzyme system, these patterns of enzyme activities cause varied degrees of lignin and cellulose breakdown at different cultivation stages. The simultaneous attack of cellulose and lignin is the preferred strategy of T. ...