New enzyme belonging to the family of molybdenum-free nitrate reductases.

A novel molybdenum-free nitrate reductase was isolated from the obligate chemolithoautotrophic and facultative anaerobic, (halo)alkaliphilic sulphur-oxidizing bacterium Thioalkalivibrio nitratireducens strain ALEN 2. The enzyme was found to contain vanadium and haem c as cofactors. Its native molecular mass was determined as 195 kDa, and the enzyme consists of four identical subunits with apparent molecular masses of 57 kDa. Apart from nitrate, the enzyme can utilize nitrite, chlorate, bromate, selenate and sulphite as electron acceptors. Moreover, it also has a haloperoxidase activity.