Purification and characterization of dissimilatory nitrate reductase from a denitrifying halophilic archaeon, Haloarcula marismortui.

Dissimilatory nitrate reductase was purified from a denitrifying halophilic archaeon, Haloarcula marismortui, to an electrophoretically homogeneous state. The purified enzyme was inferred to be a homotetramer composed of a 63 kDa polypeptide. The electron paramagnetic resonance spectrum of the purified enzyme revealed typical rhombic signals which were ascribed to Mo(V) in the Mo-molybdopterin complex. Like the bacterial membrane-bound (Nar-) enzyme, the purified enzyme supported the catalysis of chlorate. The enzyme was activated in extreme saline conditions and the values of k(cat) and K(m) toward nitrate were 145 s(-1) and 79 microM, respectively, in the presence of 2.0 M NaCl.