PURIFICATION AND KINETIC CHARACTERIZATION OF A BASIC PEROXIDASE ISOENZYME RESPONSIBLE FOR LIGNIFICATION IN GAMAY ROUGE GRAPE (VITIS-VINIFERA) BERRIES

Gamay rouge grape (Vitis vinifera) berries contain a peroxidase isoenz yme of basic pl, the peroxidase isoenzyme B5, which is the major compo nent of peroxidase polymorphism in the whole fruit, and is localized i n xylem vessels of grape berries at pigmentation. This isoenzyme has b een purified by preparative isoelectric focusing in glycerol-stabilize d 3-0-10.0 pH gradients, and characterized as regards its catalytic pr operties against coniferyl alcohol. The results showed that this isoen zyme is capable of oxidizing coniferyl alcohol with an optimal pH in t he range 3-0-6.0. K(m) values were 0-149 mm for coniferyl alcohol and 0.206 mm for H2O2. These results suggest that, although the affinity o f Gamay rouge peroxidase B-5 towards the lignification substrates is l ow compared with that shown by other peroxidases involved in lignin bi osynthesis, participation of this isoenzyme in the lignification of xy lem vessels of Gamay rouge grape berries should be taken into account.