Phenylarsonic acid is the parent compound of a group of derivatives that occur as anthropogenic environmental contaminants in both less toxic As(V) and much more toxic As(III) redox states. To elucidate the mechanisms underlying their enzymatic redox conversions, the activities of two flavin reductases, ArsH and FerA, from the soil bacterium Paracoccus denitrificans were compared. The stopped-flow data demonstrated that PhAs(V) oxidized dihydroflavin mononucleotide bound to ArsH, but not to FerA. This result proves that ArsH has some substrate specificity for organoarsenic compounds. Under aerobic conditions, both enzymes accelerated the oxidation of PhAs(III) in a catalase-sensitive manner, indicating that hydrogen peroxide acts as an intermediate. H2O2 was shown to react with PhAs(III) in a bimolecular (1:1) irreversible reaction. When exposed to blue light, flavin alone mediated rapid oxidation of PhAs(III) by O2. Photooxidation by flavin acted in concert with chemical oxidation by transiently accumulating H2O2. The described processes may be relevant in the context of arsenic ecotoxicology and remediation.

• Klíčová slova
• ArsH protein, Flavin, Hydrogen peroxide, Organoarsenicals, Photocatalysis, Redox reaction,
• MeSH
• arsenikové přípravky * chemie   metabolismus   MeSH
• flaviny * metabolismus   chemie   MeSH
• FMN-reduktasa * metabolismus   chemie   MeSH
• fotochemické procesy MeSH
• oxidace-redukce MeSH
• peroxid vodíku chemie   metabolismus   MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• arsenikové přípravky * MeSH
• diphenylarsinic acid MeSH Prohlížeč
• flaviny * MeSH
• FMN-reduktasa * MeSH
• peroxid vodíku MeSH

The Pden_5119 protein oxidizes NADH with oxygen under mediation by the bound flavin mononucleotide (FMN) and may be involved in the maintenance of the cellular redox pool. In biochemical characterization, the curve of the pH-rate dependence was bell-shaped with pKa1 = 6.6 and pKa2 = 9.2 at 2 μM FMN while it contained only a descending limb pKa of 9.7 at 50 μM FMN. The enzyme was found to undergo inactivation by reagents reactive with histidine, lysine, tyrosine, and arginine. In the first three cases, FMN exerted a protective effect against the inactivation. X-ray structural analysis coupled with site-directed mutagenesis identified three amino acid residues important to the catalysis. Structural and kinetic data suggest that His-117 plays a role in the binding and positioning of the isoalloxazine ring of FMN, Lys-82 fixes the nicotinamide ring of NADH to support the proS-hydride transfer, and Arg-116 with its positive charge promotes the reaction between dioxygen and reduced flavin.

• Klíčová slova
• FMN, NADH, Paracoccus denitrificans, dioxygen reduction,
• MeSH
• flavinmononukleotid chemie   MeSH
• flaviny chemie   MeSH
• katalýza MeSH
• kinetika MeSH
• NAD metabolismus   MeSH
• oxidace-redukce MeSH
• Paracoccus denitrificans * metabolismus   MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• flavinmononukleotid MeSH
• flaviny MeSH
• NAD MeSH
• NADH oxidase MeSH Prohlížeč