Oxidation of trans-Resveratrol by a Hypodermal Peroxidase Isoenzyme from Gamay rouge Grape (Vitis vinifera) Berries

¹ Department of Plant Biology (Plant Physiology), University of Murcia, E-30100 Murcia, Spain
² Department of Organic Chemistry, University of Murcia, E-30100 Murcia, Spain.

The ability of the hypodermal grapevine peroxidase isoenzyme B₅ to oxidize trans-resveratrol was studied. The results showed that the oxidation of trans-resveratrol by this isoenzyme was strictly dependent on H₂O₂ and follows the accepted model for peroxidase oxidations, in which compound I (Col) and compound II (Coll) appear to be the main intermediates in the catalytic cycle. The reactivity of grapevine peroxidase isoenzyme B₅ with H₂O₂ [k₁ (Col formation constant) = 1.73 µM^-1 s^-1] and with trans-resveratrol [k₃ (Coll reduction constant) = 11.9 µM^-1 s^-1], suggests that the isoenzyme reacts with H₂O₂ with a similar reactivity to that shown by other peroxidases, and that trans-resveratrol is an excellent substrate for Coll reduction. Further, the strong oxidizing activity of this basic peroxidase isoenzyme at pH 3.0 to 4.0 suggests that the peroxidase-mediated reaction is well adapted to the acidic medium of the vacuole, in which grapevine peroxidase B₅ is mainly located. These results reveal the special kinetic characteristics of the grapevine peroxidase isoenzyme B₅ to oxidize trans-resveratrol, and enable us to assign a specific metabolic function to this grapevine isoenzyme which acts as a constitutive (non-inducible) marker of disease resistance in grapevine leaves and shoots.

Key words: Vitis vinifera, kinetic characteristics, trans-resveratrol oxidation, peroxidase isoenzyme B₅, vacuole

Submitted on January 29, 1995