Xu G, Goodell B
Wood Science and Technology, University of Maine, 5755 Nutting Hall, Orono, ME 04401-5755, USA.
J Biotechnol. 2001 Apr 27;87(1):43-57. doi: 10.1016/s0168-1656(00)00430-2.
Iron, hydrogen peroxide, biochelators and oxalate are believed to play important roles in cellulose degradation by brown-rot fungi. The effect of these compounds in an 'enhanced' Fenton system on alpha-cellulose degradation was investigated specifically in regard to molecular weight distribution and cellulose-iron affinity. This study shows that the degradative ability of an ultrafiltered low molecular weight preparation of chelating compounds isolated from the brown-rot fungus Gloeophyllum trabeum (termed 'Gt chelator') increased with increasing Gt chelator concentration when the FeIII to Gt chelator ratio was greater than about 30:1. When this ratio was less than 30:1, increasing Gt chelator concentration did not accelerate cellulose degradation. In excess hydrogen peroxide, cellulose degradation increased and then decreased with increasing iron concentration when FeIII was present in excess of the Gt chelator. The critical ratio of FeIII to Gt chelator varied depending on the concentration of hydrogen peroxide in the system. Increasing iron concentration above a critical iron:chelator ratio inhibited cellulose degradation. The optimum pH for cellulose degradation mediated by Gt chelator was around 4.0. A comparison of the effects of 2,3-DHBA (a chelator that reduces iron similarly to Gt chelator) and Gt chelator with respect to cellulose degradation demonstrated the same pattern of cellulose degradation. Cellulose-iron affinity studies were conducted at three pH levels (3.6, 3.8, 4.1), and the binding constants for cellulose-FeIII, cellulose-FeII and cellulose-FeIII in the presence of Gt chelator were calculated. The binding constants for cellulose-FeIII at all three pH levels were much higher than those for cellulose-FeII, and the binding constants for cellulose-FeIII in the presence of Gt chelator were very close to those for cellulose-FeII. This is probably the result of FeIII reduction to FeII by Gt chelator and suggests that chelators from the fungus may be able to sequester iron from cellulose and reduce it in near proximity to the cellulose and thereby better promote depolymerization. The free radical generating system described has potential for use in a variety of industrial processing and pollution control applications.
铁、过氧化氢、生物螯合剂和草酸盐被认为在褐腐真菌降解纤维素的过程中发挥着重要作用。具体针对分子量分布和纤维素 - 铁亲和力，研究了这些化合物在“强化”芬顿体系中对α - 纤维素降解的影响。本研究表明，当从褐腐真菌密粘褶菌（Gloeophyllum trabeum）中分离出的超滤低分子量螯合化合物制剂（称为“Gt螯合剂”）中FeIII与Gt螯合剂的比例大于约30:1时，随着Gt螯合剂浓度的增加，其降解能力增强。当该比例小于30:1时，增加Gt螯合剂浓度并不会加速纤维素降解。在过氧化氢过量的情况下，当FeIII的量超过Gt螯合剂时，纤维素降解先随铁浓度增加而增加，然后下降。FeIII与Gt螯合剂的临界比例因体系中过氧化氢的浓度而异。铁浓度超过临界铁 - 螯合剂比例会抑制纤维素降解。由Gt螯合剂介导的纤维素降解的最佳pH约为4.0。比较2,3 - 二羟基苯甲酸（一种与Gt螯合剂类似还原铁的螯合剂）和Gt螯合剂对纤维素降解的影响，显示出相同的纤维素降解模式。在三个pH水平（3.6、3.8、4.1）下进行了纤维素 - 铁亲和力研究，并计算了在Gt螯合剂存在下纤维素 - FeIII、纤维素 - FeII和纤维素 - FeIII的结合常数。在所有三个pH水平下，纤维素 - FeIII的结合常数都远高于纤维素 - FeII的结合常数，并且在Gt螯合剂存在下纤维素 - FeIII的结合常数与纤维素 - FeII的非常接近。这可能是由于Gt螯合剂将FeIII还原为FeII的结果，表明来自真菌的螯合剂可能能够从纤维素中螯合铁并在纤维素附近将其还原，从而更好地促进解聚。所描述的自由基产生系统具有用于各种工业加工和污染控制应用的潜力。
