Resveratrol and a novel tyrosinase in Carignan grape juice

Polyphenol levels in wines are affected by the wine-making process. Resvera trol is one polyphenol which has been the subject of a commendable amount o f recent research. In this work, we found that resveratrol is immediately d egraded by tyrosinase. A novel tyrosinase was purified from Carignan grapes , The purification process included salting out and separation on a cation- exchange column, followed by gel filtration. Tyrosinase was purified in a h omogeneous form by SDS-PAGE and was characterized: its specific activity to ward 3-(3,4-dihydroxyphenyl)-L-alanine (DOPA) increased by a factor of 24 w ith an overall recovery of 3% of initial activity. The apparent molecular m ass of the purified tyrosinase was 40 kDa as determined by SDS-PAGE, and 42 kDa as determined by gel filtration. Its:activity was optimal at pH 6 and at 25 degreesC. The enzyme exhibited high activity toward phenylenediamine, epicatechin, pyrogallol, DOPA, and resveratrol. Tyrosinase activity was in hibited by KCN, thiourea, and SO2. Resveratrol levels were stable following the removal of proteins from the juice, suggesting that early spraying of grapes with SO2 is an important factor affecting the final amount of resver atrol in wine.