PLANT PHYSIOLOGY , Vol 106, Issue 3 1095-1102, Copyright © 1994 by American Society of Plant Biologists
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METABOLISM AND ENZYMOLOGY |
Characterization and Localization of a Phenoloxidase in Mung Bean Hypocotyl Cell Walls
A. Chabanet, R. Goldberg, A. M. Catesson, M. Quinet-Szely, A. M. Delaunay and L. Faye
Biomembranes et Surfaces Cellulaires Vegetales, Ecole Nozmale Superieure, 46 Rue d' Ulm, 75230 Paris Cedex 05, France (A.C., A.-M.C., M.Q.-S.)
The occurrence of proteins able to oxidize polyphenols even in the absence
of H2O2 was recently reported in mung bean (Vigna radiata L.) hypocotyl
cell wall extracts (R. Goldberg, A. Chabanet, A.M. Catesson [1993] In K.G.
Welinder, S.K. Rasmussen, C. Penel, H. Greppin, eds, Plant Peroxidases:
Biochemistry and Physiology, pp. 296-300). Therefore, the possible presence
of a laccase in the extracts was investigated using immunocytological and
biochemical approaches. An enzyme catalyzing phenol oxidation in the
presence of molecular O2 was extracted and purified from the cell walls.
This 38-kD cationic protein, like o-diphenoloxidases, was unable to oxidize
p-diphenols or p-diamines. However, it crossreacted with an anti-laccase
antiserum and, like laccases, its activity was inhibited by
N-cetyl-N,N,N-trimethylammonium bromide but not by ferulic acid salts.
Immunolabeling data showed that the 38-kD oxidase was absent from all
cellulosic cell walls. It was localized only in lignifying and lignified
cell walls. This restricted localization suggests that this laccase-like
phenoloxidase could participate in the lignification process but not in the
primary wall stiffening, which develops in the epidermal and cortical
tissues along the mung bean hypocotyl.
