The role of Cellobiose Dehydrogenases in Cellulose Biodegradation by Filamentous Fungi

白腐真菌黄孢Phanerochaete chrysosporium产生两种类型的纤维素二糖脱氢酶，即纤维素二糖氧化酶（CBO）和纤维素二糖；醌氧化还原酶（CBQ）在纤维素生物降解过程中的作用。我们已经证明CBQ是由CBO衍生而来的，在后期培养基中存在蛋白酶。因此，只有CBO与纤维素的生物降解直接相关。我已经揭示了含Fe （III）的化合物如细胞色素c是比分子氧更合适的电子受体，而分子氧在原文中被认为是CBO的电子受体。CBO本身不能溶解棉花纤维素，而且纤维素酶与CBO对棉花纤维素的溶解也没有明显的协同作用。从这个结果来看，CBO在纤维素的增溶中似乎没有任何重要的作用。与纤维素糊精相比，聚合物纤维素的还原端氧化活性非常低，这证实了这一观点。此外，纤维素的CBO吸附发生在非晶表面的一部分。从这些观察结果来看，CBO在纤维素生物降解中的作用一定是纤维素糊精或纤维素二糖代谢的一些重要功能，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，而不是分解不溶性纤维素。

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.