TY - JOUR T1 - Inhibition of Polyphenol Oxidase by Quercetin Derivatives in Grape Skin JF - American Journal of Enology and Viticulture JO - Am J Enol Vitic. SP - 109 LP - 113 DO - 10.5344/ajev.2018.17115 VL - 70 IS - 1 AU - Tohru Okuda AU - Emiko Kawai AU - Jun Harada AU - Eri Inoue AU - Masashi Hisamoto AU - Fumie Watanabe-Saito Y1 - 2019/01/01 UR - http://www.ajevonline.org/content/70/1/109.abstract N2 - Polyphenol oxidase (PPO) inhibitors were isolated from grape skin and identified as quercetin derivatives. Among the inhibitors isolated, quercetin-3-glucoside (Q3Glc) was the most potent. Kinetic analysis of the inhibitory activity toward PPO was carried out with authentic Q3Glc using catechol as substrate. The inhibition was reversible, the inhibitory mechanism obtained from Lineweaver-Burk plots indicated that Q3Glc is a competitive inhibitor, and the inhibitory constant (Ki) was 84.6 µM. ER -