Studies on biodegration mechanism of cellulose by white-rotting fungi.

生长在纤维素上的白色木腐真菌黄孢原毛革菌产生氧化还原酶纤维二糖脱氢酶（CDH）。本文研究了CDH在纤维素降解中的作用. CDH只吸附在纤维素的无定形表面上，而不吸附在纤维素的结晶表面上，表明CDH的功能不是直接分解纤维素的结晶结构.在纤维素上生长的黄孢原毛平革菌的静态培养中，CDH活性主要在菌丝体-纤维素复合体中观察到，但在培养液中不释放。此外，CDH在纤维素表面的定位是专门的纤维素酶的作用形成的裂纹。本研究通过优化培养条件，获得了大量的CDH，并在培养基中加入小牛血清，使细胞外液中CDH的产量显著提高。为了探究这一现象的原因，建立了RT-PCR检测相应mRNA水平的方法，研究了纤维二糖水解酶I（CBH I）结果表明，CDH氧化还原体系通过解除产物抑制而提高CBH Ⅰ的活性，并对pH依赖性的黄素与CDH之间的电子传递机理进行了探讨和血红素辅因子。结果表明，这一现象是由pH依赖性的蛋白质结构的构象变化的黄素含有域。

The white wood-rotting fungus Phanerochaete chrysosporium grown on cellulose produces the oxidoreductase cellobiose dehydrogenase (CDH). In this study, the role of CDH in cellulose degradation was investigated.Adsorption of CDH is occurred only on the amorphous surface of cellulose, but not on the crystalline surface, suggesting that the function of CDH is not directly responsible for decomposition of the crystalline structure of cellulose.In the static cultures of P.chrysosporium grown on cellulose, most of CDH activity is observed in the mycelium-cellulose complex, but not released in the culture solution. Moreover, localization of CDH on the cellulose surface is specialized to the crack formed by the action of cellulases. This observation is a good evicdence to suggest the cooperative function between cellulases and CDH in vivo.The optimization of cultivation condition has been elaborated to obtain a large amount of CDH.The addition of calf bovine serum in the culture medium is resulted in the significant enhancement of CDH production in the extracellular solution. To investigated the reason of this phenomenon, the method using RT-PCR for measurement of the corresponding mRNA level have been established.The interaction between cellobiohydrolase I (CBH I) and CDH in the decomposition of the microcrystalline bacterial cellulose was investigated The result demonstrated that the CDH redox system enhances CBH I activity by relieving the product inhibition.The mechanism on pH dependence of electron transportation between flavin and heme cofactors in CDH was investigated. The result suggests that this phenomenon is caused by the pH depending conformational changes of the protein structure of the flavin containing domain.