抄録
Ferredoxin-nitrite reductase (EC 1.7.7. 1), an enzyme which catalyzes the 6-electron reduction of nitrite to ammonia, has been isolated from Spinacia oleracea. The isolated enzyme was homogeneous by disc electrophoresis with polyacrylamide gel. The molecular weight of the enzyme was estimated to be 86, 000 by Ultrogel AcA 34 gel filtration. In the oxidized form, the enzyme had absorption maxima at 278, 388 (Soret band), 573 (α band) and 690nm, indicating that siroheme is directly involved in the catalysis of nitrite reduction. This absorption spectrum was modified by sulfite, hydroxylamine and cyanide. The enzyme exhibited electron paramagnetic resonance signals with g values of 6.9 and 5.2, which are characteristic ofa high spin Fe3+-siroheme in the molecule. These signals disappeared upon the addition of dithionite or nitrite. This isolated enzyme also contained four moles of labile sulfide and 7g-atoms of iron per 86, 000g of protein.
