Kirk T K, Mozuch M D, Tien M
Biochem J. 1985 Mar 1;226(2):455-60. doi: 10.1042/bj2260455.
Hydroxyl radical (HO.) has been implicated in the degradation of lignin by Phanerochaete chrysosporium. This study assessed the possible involvement of HO. in degradation of lignin substructural models by intact cultures and by an extracellular ligninase isolated from the cultures. Two non-phenolic lignin model compounds [aryl-C(alpha)HOH-C(beta)HR-C(gamma)H2OH, in which R = aryl (beta-1) or R = O-aryl (beta-O-4)] were degraded by cultures, by the purified ligninase, and by Fenton's reagent (H2O2 + Fe2+), which generates HO.. The ligninase and the cultures formed similar products, derived via an initial cleavage between C(alpha) and C(beta) (known to be an important biodegradative reaction), indicating that the ligninase is responsible for model degradation in cultures. Products from the Fenton degradation were mainly polar phenolics that exhibited little similarity to those from the biological systems. Mass-spectral analysis, however, revealed traces of the same products in the Fenton reaction as seen in the biological reactions; even so, an 18O2-incorporation study showed that the mechanism of formation differed. E.s.r. spectroscopy with a spin-trapping agent readily detected HO. in the Fenton system, but indicated that no HO. is formed during ligninase catalysis. We conclude, therefore that HO. is not involved in fungal C(alpha)-C(beta) cleavage in the beta-1 and beta-O-4 models and, by extension, in the same reaction in lignin.
羟基自由基（HO.）被认为与黄孢原毛平革菌降解木质素有关。本研究评估了HO.在完整培养物以及从培养物中分离出的细胞外木质素酶对木质素亚结构模型降解过程中可能的参与情况。两种非酚类木质素模型化合物[芳基-C(α)HOH-C(β)HR-C(γ)H2OH，其中R = 芳基（β-1）或R = O-芳基（β-O-4）]被培养物、纯化的木质素酶以及产生HO.的芬顿试剂（H2O2 + Fe2+）降解。木质素酶和培养物形成了相似的产物，这些产物是通过C(α)和C(β)之间的初始裂解产生的（已知这是一个重要的生物降解反应），这表明木质素酶负责培养物中模型的降解。芬顿降解产生的产物主要是极性酚类，与生物系统产生的产物几乎没有相似性。然而，质谱分析显示，芬顿反应中存在与生物反应中相同产物的痕迹；即便如此，一项18O2掺入研究表明其形成机制不同。使用自旋捕获剂的电子顺磁共振光谱很容易在芬顿体系中检测到HO.，但表明在木质素酶催化过程中不会形成HO.。因此，我们得出结论，HO.不参与β-1和β-O-4模型中真菌的C(α)-C(β)裂解，进而也不参与木质素中的相同反应。
