tailieunhanh - Báo cáo khoa học: Production and utilization of hydrogen peroxide associated with melanogenesis and tyrosinase-mediated oxidations of DOPA and dopamine

The synthesis and involvement of H2O2 during the early stages of melano-genesis involving the oxidations of DOPA and dopamine (diphenolase activity) were established by two sensitive and specific electrochemical detection systems. Catalase-treated reaction mixtures showed diminished rates of H2O2 production during the autoxidation and tyrosinase-mediated oxidation of both diphenols. | ềFEBS Journal Production and utilization of hydrogen peroxide associated with melanogenesis and tyrosinase-mediated oxidations of DOPA and dopamine Maristella Mastore1 Lara Kohler2 and Anthony J. Nappi2 1 University degli Studi dell Insubria Dipartimento di Biologia Strutturale e Funzionale Laboratorio di Immunologia Comparata Varese Italy 2 AnimalHeath and BiomedicalSciences University of Wisconsin-Madison Madison WI USA Keywords hydrogen peroxide melanogenesis reactive intermediates of oxygen tyrosinase Correspondence A. J. Nappi AnimalHeath and Biomedical Sciences University of Wisconsin-Madison Madison WI 53706 USA Fax 1 608 2627420 Tel 1 608 2622618 E-mail anappi@ Received 10 December 2004 revised 3 February 2005 accepted 11 March 2005 doi The synthesis and involvement of H2O2 during the early stages of melanogenesis involving the oxidations of DOPA and dopamine diphenolase activity were established by two sensitive and specific electrochemical detection systems. Catalase-treated reaction mixtures showed diminished rates of H2O2 production during the autoxidation and tyrosinase-mediated oxidation of both diphenols. Inhibition studies with the radical scavenger resveratrol revealed the involvement in these reactions of additional reactive intermediate of oxygen ROI one of which appears to be superoxide anion. There was no evidence to suggest that H2O2 or any other ROI was produced during the tyrosinase-mediated conversion of tyrosine to DOPA monophenolase activity . Establishing by electrochemical methods the endogenous production H2O2 in real time confirms recent reports based in large part on the use of exogenous H2O2 that tyrosinase can manifest both catalase and peroxidase activities. The detection of ROI in tyrosinase-mediated in vitro reactions provides evidence for sequential univalent reductions of O2 most likely occurring at the enzyme active site copper. Collectively these observations focus .