Goodwin D C, Barr D P, Aust S D, Grover T A
Biotechnology Center, Utah State University, Logan 84322-4700.
Arch Biochem Biophys. 1994 Dec;315(2):267-72. doi: 10.1006/abbi.1994.1499.
Reduction may be an important step in the degradation of some highly oxidized environmental pollutants by Phanerochaete chrysosporium. Lignin peroxidases (LiP) from P. chrysosporium are able to catalyze reductive reactions using veratryl alcohol (VA) as a mediator and either oxalate or EDTA as electron donors. Reduction of oxygen to superoxide, monitored by oxygen consumption, was used as a measure of the reductive activity of LiP. In the presence of EDTA, the rate of O2 reduction catalyzed by LiP decreased with time and increasing concentrations of H2O2. When oxalate replaced EDTA, LiP-catalyzed O2 reduction did not decrease with time, and increasing concentrations of H2O2 increased the duration and extent of O2 reduction. LiP was converted to the compound III state in the presence of EDTA, H2O2, and veratryl alcohol. When oxalate replaced EDTA, compound II was observed. The importance of the veratryl alcohol cation radical (VA.+) in the conversion of LiP compound III to active enzyme has been previously examined (D.P. Barr and S.D. Aust, 1994, Arch. Biochem. Biophys. 311, 378-382). We propose that rapid reduction of VA.+ by EDTA results in accumulation of LiP compound III and the loss of activity resulting in a decrease in LiP-catalyzed reduction reactions. Oxalate is less effective in reducing the VA.+, therefore, some VA.+ remains to convert compound III to active enzyme and maintain LiP-catalyzed reduction reactions. Thus oxalate, a normal secondary metabolite of P. chrysosporium, is a suitable candidate for mediating reduction reactions by LiP in vivo.
还原作用可能是黄孢原毛平革菌降解某些高度氧化的环境污染物的一个重要步骤。黄孢原毛平革菌的木质素过氧化物酶（LiP）能够以藜芦醇（VA）作为介体，以草酸盐或乙二胺四乙酸（EDTA）作为电子供体催化还原反应。通过耗氧量监测氧气还原为超氧化物的过程，以此作为LiP还原活性的一种衡量指标。在EDTA存在的情况下，LiP催化的O₂还原速率随时间以及H₂O₂浓度的增加而降低。当草酸盐取代EDTA时，LiP催化的O₂还原不会随时间降低，并且H₂O₂浓度的增加会增加O₂还原的持续时间和程度。在EDTA、H₂O₂和藜芦醇存在的情况下，LiP会转化为化合物III状态。当草酸盐取代EDTA时，会观察到化合物II。之前已经研究过藜芦醇阳离子自由基（VA⁺）在LiP化合物III转化为活性酶过程中的重要性（D.P. Barr和S.D. Aust，1994年，《生物化学与生物物理学报》311卷，378 - 382页）。我们提出，EDTA对VA⁺的快速还原导致LiP化合物III的积累以及活性丧失，从而导致LiP催化的还原反应减少。草酸盐在还原VA⁺方面效果较差，因此，一些VA⁺仍然可以将化合物III转化为活性酶并维持LiP催化的还原反应。因此，草酸盐作为黄孢原毛平革菌的一种正常次生代谢产物，是在体内介导LiP还原反应的合适候选物。
