THE ROLE OF OXALATE IN LIGNIN PEROXIDASE-CATALYZED REDUCTION - PROTECTION FROM COMPOUND-III ACCUMULATION

Reduction may be an important step in the degradation of some highly o xidized environmental pollutants by Phanerochaete chrysosporium. Ligni n peroxidases (LiP) from P. chrysosporium are able to catalyze reducti ve reactions using veratryl alcohol (VA) as a mediator and either oxal ate or EDTA as electron donors. Reduction of oxygen to superoxide, mon itored by oxygen consumption, was used as a measure of the reductive a ctivity of LiP. In the presence of EDTA, the rate of O-2 reduction cat alyzed by LiP decreased with time and increasing concentrations of H2O 2. When oxalate replaced EDTA, LiP-catalyzed O-2 reduction did not dec rease with time, and increasing concentrations of H2O2 increased the d uration and extent of O-2 reduction. LiP was converted to the compound III state in the presence of EDTA, H2O2, and veratryl alcohol. When o xalate replaced EDTA, compound II was observed. The importance of the veratryl alcohol cation radical (VA(+)) in the conversion of LiP compo und III to active enzyme has been previously examined (D. P. Barr and S. D. Aust, 1994, Arch. Biochem. Biophys. 311, 378-382). We propose th at rapid reduction of VA(+) by EDTA results in accumulation of LiP com pound III and the loss of activity resulting in a decrease in LiP-cata lyzed reduction reactions. Oxalate is less effective in reducing the V A(+), 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 candid ate for mediating reduction reactions by LiP in vivo. (C) 1994 Academi c Press, Inc.