Banci L, Ciofi-Baffoni S, Tien M
Department of Chemistry, University of Florence, Italy.
Biochemistry. 1999 Mar 9;38(10):3205-10. doi: 10.1021/bi982139g.
The oxidation of phenolic oligomers by lignin and manganese peroxidases was studied by transient-state kinetic methods. The reactivity of peroxidase intermediates compound I and compound II was studied with the phenol guaiacol along with a beta-O-4 phenolic dimer, trimer, and tetramer. Compound I of both peroxidases is much more reactive than compound II. The rate constants for these substrates with Mn peroxidase compound I range from 1.0 x 10(5) M-1 s-1 for guaiacol to 1.1 x 10(3) M-1 s-1 for the tetramer. Reactivity is much higher with lignin peroxidase compound I with rate constants ranging from 1.2 x 10(6) M-1s-1 for guaiacol to 3.6 x 10(5) M-1 s-1 for the tetramer. Rate constants with compound II are much lower with Mn peroxidase exhibiting very little reactivity. The rate constants dramatically decreased with both peroxidases as the size of the substrate increased. The extent of the decrease was much more dramatic with Mn peroxidase, leading us to conclude that, despite its ability to oxidize phenols, Mn2+ is the only physiologically significant substrate. The rate decrease associated with increasing substrate size was more gradual with lignin peroxidase. These data indicate that whereas Mn peroxidase cannot efficiently directly oxidize the lignin polymer, lignin peroxidase is well suited for direct oxidation of polymeric lignin.
采用瞬态动力学方法研究了木质素和锰过氧化物酶对酚类低聚物的氧化作用。用愈创木酚以及一种β-O-4酚二聚体、三聚体和四聚体研究了过氧化物酶中间体化合物I和化合物II的反应活性。两种过氧化物酶的化合物I比化合物II的反应活性高得多。这些底物与锰过氧化物酶化合物I的速率常数范围从愈创木酚的1.0×10⁵ M⁻¹ s⁻¹到四聚体的1.1×10³ M⁻¹ s⁻¹。木质素过氧化物酶化合物I的反应活性要高得多，速率常数范围从愈创木酚的1.2×10⁶ M⁻¹ s⁻¹到四聚体的3.6×10⁵ M⁻¹ s⁻¹。化合物II的速率常数要低得多，锰过氧化物酶的反应活性非常小。随着底物尺寸的增加，两种过氧化物酶的速率常数都显著降低。锰过氧化物酶的降低程度更为显著，这使我们得出结论，尽管它有氧化酚类的能力，但Mn²⁺是唯一具有生理意义的底物。木质素过氧化物酶随着底物尺寸增加而导致的速率降低更为平缓。这些数据表明，虽然锰过氧化物酶不能有效地直接氧化木质素聚合物，但木质素过氧化物酶非常适合直接氧化聚合木质素。
