Kuan I C, Tien M
Department of Molecular and Cell Biology, Pennsylvania State University, University Park 16802.
Proc Natl Acad Sci U S A. 1993 Feb 15;90(4):1242-6. doi: 10.1073/pnas.90.4.1242.
Oxalate is produced by numerous wood-degrading fungi. Our studies here show that the white-rot fungus Phanerochaete chrysosporium produces extracellular oxalate under conditions that induce synthesis of the ligninolytic system. Little or no oxalate was detected in cultures grown under high nutrient nitrogen or carbon. This extracellular oxalate was identified and quantitated by HPLC. Its identity was further substantiated by its decomposition by the enzyme oxalate oxidase. The oxalate content of the extracellular fluid (peaking at 60 microM) paralleled the extracellular activity of the lignin-degrading enzyme, Mn peroxidase. Significantly, we demonstrated that oxalate, at physiological concentrations, substantially stimulated Mn peroxidase-catalyzed phenol red oxidation, presumably by its ability to chelate Mn. Stopped flow studies also indicate that oxalate accelerates the turnover of Mn peroxidase. Furthermore, we discovered that oxalate can support Mn peroxidase-catalyzed oxidations in the absence of exogenous H2O2 and in the presence of dioxygen. These results allow us to propose an important role for oxalate, a ubiquitous compound produced by wood-destroying fungi, in lignin biodegradation.
草酸由多种木材降解真菌产生。我们在此的研究表明，白腐真菌黄孢原毛平革菌在诱导木质素降解系统合成的条件下会产生细胞外草酸。在高氮或高碳营养条件下培养的菌株中检测到很少或几乎没有草酸。通过高效液相色谱法对这种细胞外草酸进行了鉴定和定量。草酸氧化酶对其分解进一步证实了其特性。细胞外液中的草酸含量（峰值为60微摩尔）与木质素降解酶锰过氧化物酶的细胞外活性平行。值得注意的是，我们证明，在生理浓度下，草酸可能通过其螯合锰的能力，极大地刺激了锰过氧化物酶催化的酚红氧化。停流研究还表明，草酸加速了锰过氧化物酶的周转。此外，我们发现，在没有外源过氧化氢且存在双氧的情况下，草酸能够支持锰过氧化物酶催化的氧化反应。这些结果使我们能够提出，草酸这种由木材破坏真菌产生的普遍存在的化合物，在木质素生物降解中具有重要作用。
