"Nitrite reductase from Sinorhizobium meliloti 2011: a Cu-containing Enzyme that Catalyses the Reduction of Nitrite to Nitric Oxide"

J. C. CRISTALDI; F. M. FERRONI; N. I. NEUMAN; P. J. GONZÁLEZ; A. C. RIZZI; M. G. RIVAS; C. D. BRONDINO

Chascomús, Buenos Aires

Encuentro; Fourth Latin American Meeting on Biological Inorganic Chemistry (LABIC),; 2014

Copper-containing nitrite reductase (Nir) is a key enzyme in the dissimilatory reduction of nitrate to dinitrogen in denitrifying bacteria. The Nir from Sinorhizobium meliloti 2011 (SmNir), a rhizobia bacterium that lives in root nodules of legumes and is widely used in agriculture as fertilizers1,is a homotrimeric protein that contains two Cu centers, one of type 1 (T1; also blue copper) and other of type 2 (T2; also normal copper). The enzyme catalyzes the reduction of NO2- to NO (Eo? = 370 mV) through a catalytic mechanism that involves the binding of nitrite to T2 and the subsequent reduction to NO by reducing equivalents given by an external physiological electron donor through the T1 center  (Figure 1)2,3. We report here the characterization of the metal centers involved in the electron transfer chain of SmNir. We also analyze the role of the physiological electron donor of SmNir, a copper-containing pseudoazurin (SmPaz) in modulating the reduction potentials of the copper centers in SmNir.