title: Tyrosinase inhibitory polyphenols from roots of Morus lhou.
abstract: Twelve polyphenols (1-12) possessing tyrosinase inhibitory properties were isolated from the methanol (95%) extract of Morus lhou. The isolated compounds consisted of four flavanones (1-4), four flavones (5-8), and four phenylbenzofuranes (9-12). Moracin derivative 12 proved to be new a compound which was fully characterized. Compounds 1-12 were evaluated for both monophenolase and diphenolase (the two steps catalyzed by tyrosinase) inhibition to identify the structural characteristics required for mushroom tyrosinase inhibition. We observed that all parent compounds (1, 5, and 9) possessing an unsubstituted resorcinol group were highly effective inhibitors of monophenolase activity (IC(50) values of 1.3, 1.2, and 7.4 microM). The potency of the inhibitors diminished with alkyl substitution on either the aromatic ring or the hydroxyl functions. Interestingly, flavone 5 was shown to possess only monophenolase inhibitory activity, but flavanone 1 and phenylbenzofuran 9 inhibited diphenolase as well as monophenolase significantly. The inhibitory mode of these species was also dependent upon the skeleton: phenylbenzofuran 9 manifested a simple competitive inhibition mode for monophenolase and diphenolase; on the other hand flavanone 1 (monophenolase, k(3) = 0.1966 min(-1) microM(-1), k(4) = 0.0082 min(-1), and K(i)(app) = 0.0468 microM; diphenolase, k(3) = 0.0014 min(-1) microM(-1), k(4) = 0.0013 min(-1), and K(i)(app) = 0.8996 microM) and flavone 5 both showed time-dependent inhibition against monophenolase. Compound 1 operated according to the simple reversible slow binding model whereas compound 5 operated under the enzyme isomerization model.
authors.affiliation: Division of Applied Life Science (BK21 Program), EB-NCRC, Institute of Agriculture & Life Science, Graduate School of Gyeongsang National University, Jinju 660-701, Korea.
authors.forename: Seong Hun
authors.initials: SH
authors.lastname: Jeong
authors.forename: Young Bae
authors.initials: YB
authors.lastname: Ryu
authors.forename: Marcus J
authors.initials: MJ
authors.lastname: Curtis-Long
authors.forename: Hyung Won
authors.initials: HW
authors.lastname: Ryu
authors.forename: Yoon Su
authors.initials: YS
authors.lastname: Baek
authors.forename: Jae Eun
authors.initials: JE
authors.lastname: Kang
authors.forename: Woo Song
authors.initials: WS
authors.lastname: Lee
authors.forename: Ki Hun
authors.initials: KH
authors.lastname: Park
mesh_terms: D004791:Enzyme Inhibitors / Q000737:chemistry / Q000302:isolation & purification* / Q000494:pharmacology; D005419:Flavonoids / Q000302:isolation & purification* / Q000494:pharmacology; D007700:Kinetics; D014442:Monophenol Monooxygenase / Q000037:antagonists & inhibitors* / Q000378:metabolism; D031625:Morus / Q000737:chemistry* / Q000201:enzymology; D010636:Phenols / Q000302:isolation & purification* / Q000494:pharmacology; D018517:Plant Roots / Q000737:chemistry*; D059808:Polyphenols
chemical_list: D004791:Enzyme Inhibitors; D005419:Flavonoids; D010636:Phenols; D059808:Polyphenols; D014442:Monophenol Monooxygenase