The role of Cellobiose Dehydrogenases in Cellulose Biodegradation by Filamentous Fungi

白色腐烂真菌黄孢原毛平革菌(Phanerochaete Chrysosporium)在降解纤维素的过程中产生两种类型的纤维二糖脱氢酶，即纤维二糖氧化酶(CBO)和纤维二糖；我们已经证明了CBQ是由CBO通过后期培养基中共存的蛋白水解酶产生的。因此，只有CBO必须与纤维素的生物降解直接相关。结果表明，细胞色素C等含铁化合物比分子氧更适合作为CBO的电子受体，CBO本身不能溶解棉纤维，纤维素酶和CBO之间也没有明显的协同增溶作用。从这一结果来看，CBO似乎在纤维素的增溶中没有任何重要作用。与纤维糊精相比，聚合物纤维素中还原端的氧化活性非常低，证实了这一观点。由此可见，CBO在纤维素生物降解中的作用可能是纤维糊精或纤维二糖代谢的某些重要功能，例如代谢物的膜运输或这些化合物的代谢与能量产生之间的联系，而不是不溶性纤维素的分解。

The white rotting fungi, Phanerochaete chrysosporium, produces two types of cellobiose dehydrogenases, namely cellobiose oxidase (CBO) and cellobiose ; quinone oxidoreductase (CBQ), in the course of cellulose biodegradation. We have demonstrated that CBQ is derived from CBO by proteases co-exisisted in the culture medium of the later stage. Therefore, only CBO must be associated directly on cellulose biodegradation. I have revealed that the Fe (III) containing compound such as cytochrome c are more suitable electron acceptor than molecular oxygen, which was thought as a electron acceptor for CBO in the original article.CBO is unable to solubilize cotton cellulose by itself, but also there is no obvious synergistic effects between cellulases and CBO on solubilization of cotton cellulose. From this result, CBO seems not to have any important role in the solubilization of cellulose. This idea is confirmed by the very low activity for the oxidation of the reducing ends in polymeric cellulose compared with those for cellodexrins. Furthermore, the CBO adsorption of cellulose occurs on a part of the amorphous surface.From all these observations, the role of CBO in the cellulose biodegradation must be some important function of cellodextrin or cellobiose metabolism, for example, membrane transportation of metabolites or the linkage between metabolism of these compounds and energy production, rather than the decomposition of insoluble cellulose.