Coniferyl alcohol oxidase, anew enzyme of lignification

Abstract

Coniferyl alcohol oxidase (CAO), a catechol oxidase (o-diphenol:oxygen oxidoreductase, E.C.1.10.3.1) specifically associated with lignification during wood formation in conifers, is described and its activity is compared with that of peroxidase. CAO activity is not affected by provision of H2O2, and although CAO is an O2-requiring enzyme able to oxidize substrates in common with laccase, CAO is distinct from laccase in catalytic rate, amino acid composition, response to effectors, copper content and type, protein size, and immunodetectability. Peroxidase activity, readily detected in phloem, cambium and xylem, was inversely correlated with lignification. In contrast, CAO activity was restricted to the lignifying zone. Peroxide and superoxide anion were found in the phloem and cambial zone, respectively, but a pool of H2O2 in support of lignification could not be detected in lignifying xylem or elsewhere. Additional evidence has indicated that coniferin hydrolysis may be the rate limiting step in the supply of coniferyl alcohol for oxidation by CAO.