EPR and Kinetic Studies on NapA from Desulfovibrio desulfuricans ATCC 27774.

P.J. GONZÁLEZ; M.G. RIVAS; C.D. BRONDINO; I. MOURA; J.J.G. MOURA

Montpellier (France)

Congreso; 15th IUPAB and 5th EBSA International Biophysics Congress.; 2005

Nitrate reductases are enzymes that catalyze the conversion of nitrate to nitrite. EPR and kinetic studies has been made in the periplasmic nitrate reductase isolated from the sulfate-reducing bacteria Desulfovibrio desulfuricans ATCC 27774. This protein, belonging to the DMSO reductase family of mononuclear Mo-containing enzymes, is constituted by a single 80 kDa subunit and contains a Mo-bisMGD cofactor and a [4Fe-4S] cluster. Potentiometric-EPR-monitored redox titrations, carried out with and without nitrate in the potential range +200 / -500 mV, and EPR studies of the enzyme in both catalytic and inhibited conditions, reveal distinct types of Mo(V) EPR active species. The possible structures and the role in catalysis of the distinct Mo(V) species detected by EPR are discussed.