OXIDATION OF TRANS-RESVERATROL BY A HYPODERMAL PEROXIDASE ISOENZYME FROM GAMAY ROUGE GRAPE (VITIS-VINIFERA) BERRIES

The ability of the hypodermal grapevine peroxidase isoenzyme B-5 to ox idize trans-resveratrol was studied. The results showed that the oxida tion of trans-resveratrol by this isoenzyme was strictly dependent on H2O2 and follows the accepted model for peroxidase oxidations, in whic h compound I (CoI) and compound II (CoII) appear to be the main interm ediates in the catalytic cycle. The reactivity of grapevine peroxidase isoenzyme B-5 with H2O2 [k(1) (CoI formation constant) = 1.73 mu M(-1 ) s(-1)] and with trans-resveratrol [k(3) (CoII reduction constant) = 11.9 mu M(-1) s(-1)], suggests that the isoenzyme reacts with H2O2 wit h a similar reactivity to that shown by other peroxidases, and that tr ans-resveratrol is an excellent substrate for CoII reduction. Further, the strong oxidizing activity of this basic peroxidase isoenzyme at p H 3.0 to 4.0 suggests that the peroxidase-mediated reaction is well ad apted to the acidic medium of the vacuole, in which grapevine peroxida se B-5 is mainly located. These results reveal the special kinetic cha racteristics of the grapevine peroxidase isoenzyme B-5 to oxidize tran s-resveratrol, and enable us to assign a specific metabolic function t o this grapevine isoenzyme which acts as a constitutive (non-inducible ) marker of disease resistance in grapevine leaves and shoots.