Purification, stabilization and characterization of nitrite reductase from barley roots

Nitrite reductase (NiR) isolated from barley (Hordeum vulgare L.) roots was stabilized in a buffer solution containing a sulfhydryl-reducing reagent and glycerol. The enzyme was purified 340fold by ammonium sulfate fractionation and chromatography on DEAE-Sephadex A-50, Sephadex G-200 and DEAE-cellulose. Purified NiR had a specific activity of 28 μmol NO2 (-) reduced min(-1) mg(-1) of protein. The purified preparation was reddishbrown having absorption maxima at 282, 388 and 577 nm. The barley-root enzyme was almost identical with spinach-leaf NiR with respect to molecular weight, isoelectric point, pH stability, pH optimum, affinity for substrate, behavior toward inhibitors. It is concluded that NiR is the same enzymatic entity regardless of its localization in photosynthetic or nonchlorophyllous tissues. The electron-transport system for NiR in root tissue is discussed in comparison with that in leaf tissue.