Wheat prolamine crosslinking through dityrosine formation catalyzed by peroxidases: improvement in the modification of a poorly accessible substrate by "indirect" catalysis
"Enzyme-assisted" oxidative polymerization of wheat gliadins was performed in an attempt to obtain new protein-based networks. Two plant peroxidases (soybean and horseradish) were used to induce the dimerization of tyrosine residues. The results show that tyrosines are poorly modified by these enzymes in an aqueous medium (dityrosine corresponded to 2% of the total amount of tyrosine). Two approaches were tested to overcome problems relating to accessibility to the target tyrosines: First, the efficiency of protein crosslinking via tyrosine-tyrosine aromatic ring condensation was enhanced in water when the proteins were oxidized by a fungus peroxidase (manganese-dependent peroxidase from Phanerochaete chrysosporium), which acts according to an indirect catalysis mechanism (up to 12% of the total amount of tyrosine is recovered under a dimeric form). Second, when the gliadins were dispersed in a water/dioxane (3/1) mixed solvent system, the tyrosines were more accessible on the protein surface, and similar yields were obtained with both types of peroxidase. The two types of catalysis (contact and indirect) are considered from the standpoint of the accessibility of the target residues. Enzymatic oxidations were also performed on synthetic peptides mimicking the repeatitive domains of gliadins. The results show that exposure of tyrosine to the solvent may not be sufficient to induce dityrosine formation. The mechanical properties of some films obtained from peroxidase-treated gliadins were investigated to correlate protein crosslinking with a potential application. One effect of the enzymatic treatment was to increase the tensile strength of the films. Copyright 1999 John Wiley & Sons, Inc.
Michon
T
Division of Chemical Engineering 210-41 California Institute of Technology 1200E, California Boulevard, Pasadena, California 91125, USA.
Wang
W
Ferrasson
E
Gueguen
J