Kawai S, Jensen K A, Bao W, Hammel K E
Institute for Microbial and Biochemical Technology, USDA Forest Products Laboratory, Madison, Wisconsin 53705, USA.
Appl Environ Microbiol. 1995 Sep;61(9):3407-14. doi: 10.1128/aem.61.9.3407-3414.1995.
Lignin model dimers are valuable tools for the elucidation of microbial ligninolytic mechanisms, but their low molecular weight (MW) makes them susceptible to nonligninolytic intracellular metabolism. To address this problem, we prepared lignin models in which unlabeled and alpha-14C-labeled beta-O-4-linked dimers were covalently attached to 8,000-MW polyethylene glycol (PEG) or to 45,000-MW polystyrene (PS). The water-soluble PEG-linked model was mineralized extensively in liquid medium and in solid wood cultures by the white rot fungus Phanerochaete chrysosporium, whereas the water-insoluble PS-linked model was not. Gel permeation chromatography showed that P. chrysosporium degraded the PEG-linked model by cleaving its lignin dimer substructure rather than its PEG moiety. C alpha-C beta cleavage was the major fate of the PEG-linked model after incubation with P. chrysosporium in vivo and also after oxidation with P. chrysosporium lignin peroxidase in vitro. The brown rot fungus Gloeophyllum trabeum, which unlike P. chrysosporium lacks a vigorous extracellular ligninolytic system, was unable to degrade the PEG-linked model efficiently. These results show that PEG-linked lignin models are a marked improvement over the low-MW models that have been used in the past.
木质素模型二聚体是阐明微生物木质素分解机制的重要工具，但其低分子量使其易受非木质素分解性细胞内代谢的影响。为了解决这个问题，我们制备了木质素模型，其中未标记的和α-14C标记的β-O-4连接的二聚体共价连接到8000分子量的聚乙二醇（PEG）或45000分子量的聚苯乙烯（PS）上。水溶性PEG连接的模型在液体培养基和固体木材培养物中被白腐真菌黄孢原毛平革菌广泛矿化，而水不溶性PS连接的模型则没有。凝胶渗透色谱表明，黄孢原毛平革菌通过切割其木质素二聚体亚结构而非其PEG部分来降解PEG连接的模型。在体内与黄孢原毛平革菌孵育后以及在体外被黄孢原毛平革菌木质素过氧化物酶氧化后，PEG连接模型的主要命运是Cα-Cβ裂解。与黄孢原毛平革菌不同，褐腐真菌密粘褶菌缺乏强大的细胞外木质素分解系统，无法有效降解PEG连接的模型。这些结果表明，PEG连接的木质素模型比过去使用的低分子量模型有显著改进。
