Production and chemiluminescent free radical reactions of glyoxal in lipidperoxidation of linoleic acid by the ligninolytic enzyme, manganese peroxidase

Glyoxal is a key compound involved in glyoxal oxidase (GLOX)-dependent prod uction of glyoxylate, oxalate and H2O2 by lignin-degrading basidiomycetes. In this paper, we report that glyoxal was produced from a metabolite of lig ninolytic fungi, linoleic acid. by manganese peroxidase (MnP)-dependent lip id peroxidation. In the absence of the parent substrate of linoleic acid, t he dialdehyde was oxidized by MnP and Mn(III) chelate to start free radical reactions with emission of chemiluminescence at 700-710 nm. The spectrosco pic profile of the light emission is distinguishable from (a) singlet oxyge n, (b) triplet carbonyls from dioxetane and alpha -hydroxyperoxyl radicals, and (c) biacyl triplet formed by the coupling of two acyl radicals. The ph oton emission of glyoxal by MnP was activated by co-oxidation of tartrate. The MnP-dependent oxidation of glyoxal in tartrate buffers continued for 10 days without addition of exogenous H2O2. The importance of these results i s discussed in relation to the free radical chemistry of lignin biodegradat ion by wood rot fungi.