Purification and molecular properties of nitrite reductase from Anabaena sp. 7119

Abstract

Ferredoxin‐nitrite reductase (EC 1.7.7.1.) from the cyanobacteria Anabaena sp. 7119 has been purified 763‐fold with a specific activity of 21.5 units/nig protein (0.358 μkatals/mg). The enzyme has a molecular mass of 52,000 daltons with a Stokes radius of 3.09 nm and a sedimentation coefficient of 4.07 S. The cellular level of nitrite reductase activity gradually increases in response to the addition of increasing amounts of iron to the culture medium.When partially purified nitrite reductase preparations are subjected to sucrose‐density‐gradient centrifugation there is a dose correspondence between nitrite reductase activity and absorbance at 400 nm. This suggests the association of a heme chromophore with the enzyme. Furthermore, the presence of an iron‐sulfur center is suggested by a close association of acid‐labile sulfide with nitrite reductase activity. Carbon monoxide inhibits nitrite reductase activity. The nature and kinetics of this reaction are comparable to other siroheme‐containing nitrite reductases.