PHYSIOLOGICAL REGULATION OF GLYOXAL OXIDASE FROM PHANEROCHAETE-CHRYSOSPORIUM BY PEROXIDASE SYSTEMS

Glyoxal oxidase (GLOX) is an H2O2-producing enzyme secreted by lignino lytic cultures of Phanerochaete chrysosporium. The oxidase is reversib ly inactivated during purification, but can be reactived when coupled to lignin peroxidase (LiP) with veratryl alcohol as the peroxidase sub strate. To characterize the modulation of this extracellular oxidase a ctivity, we studied effects of pH, peroxide concentration, peroxidase source (fungal vs plant), and peroxidase substrate with recombinant GL OX (rGLOX). Our results show that a peroxidase system is not required for rGLOX activity. However, the activity is transient and the enzyme is partly and reversibly inactivated by the produced peroxide. rGLOX a ctivity is more sustained at pH 6 than pH 4.5, and therefore the activ ation at pH 4.5 by a coupled peroxidase system is more clearly demonst rable. Results with peroxidase substrates of widely varying redox pote ntials strongly suggest that oxidized intermediates produced by couple d peroxidases are the GLOX activators. Both LiP and horseradish peroxi dase (HRP) may be used to fully activate rGLOX using methoxybenzenes a s peroxidase substrates. Notably, rGLOX is activated when lignin itsel f is used in coupled reactions with Lip. In contrast, guaiacol and cat echols are both inactivating and lignin degradation products are expec ted to have similar effects. Taken together, our results suggest that ligninolysis by peroxidase could be regulated by GLOX activity and inf luenced by the presence of veratryl alcohol, lignin, and lignin degrad ation products. Such coordinated metabolism would influence the kineti cs of free radical generation by the Lips and, therefore, the overall efficiency of lignin depolymerization.