Oral communication, CS12 / C54

Official XXIst International Pigment Cell Conference website - 21-24 Sept 2011, Bordeaux - France | updated: September 04 2011

Pigment Melanin Mediates a Redox Reaction between Adsorbed Nitric Oxide and O2 in vitro

SPEAKER J. Menter #whois submiter ?
AUTHOR(s) J. Menter, C. Nokkaew, A. Sprewell, D. Eatman, S. Harris-Hooker

BACKGROUND AND OBJECTIVES: Pigment melanin can adsorb molecular O2, scavenge nitric oxide (NO) and thereby couple a redox reaction between them. In this work, we show formation of peroxynitrite (ONOO-) in the presence but not in the absence of melanin. METHODS: NO generated by DEA/NO or SNAP was dialyzed into membranes containing purified sepia melanin in 0.1 M phosphate buffer, pH 7.4 or control buffer alone. NO was measured as nitrite and nitrate via the Greiss methodology and by the DAF fluorescence assay. Peroxynitrite was detected by selective scavenging with 3.3 µM MCP or via detection of nitrotyrosine in cultured fibroblasts. H2O2 was monitored by the scopoletin/peroxidase assay. Appropriate controls were used. RESULTS: Dialyzate NO concentrations were significantly lower in the test dialyzates than in controls. In the test systems in vitro we detected significant amounts of peroxynitrite but little or no hydrogen peroxide. No significant amounts of either of these were detected in the absence of melanin. In cultured fibroblasts, we observed positive staining for nitrotyrosine in the presence, but not in the absence of melanin. CONCLUSIONS: Sepia melanin can couple the redox reaction between adsorbed NO and O2 to afford ONOO – via a superoxide intermediate. Superoxide can undergo “pseudodismutation” to H2O2 and O2 by melanin or reaction with NO. Peroxide is scavenged by melanin, and is not detected in significant amounts. Supported in Part by MBRS Grant #GM 08248, RCMI Grant #RR 03034 and DOD Grant # W911NF – 10 – 1 – 0448.



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