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Mechanism of nitrite reduction in chloroplasts

1963; Elsevier BV; Volume: 10; Issue: 4 Linguagem: Inglês

10.1016/0006-291x(63)90528-x

1090-2104

M. Losada, A. Paneque, Juanma Ramírez, Francisca F. del Campo,

Plant Micronutrient Interactions and Effects

This chapter describes ferredoxin-nitrite reductase. Ferredoxin-nitrite reductase (EC 1.7.7.1) is the second enzyme component of the photosynthetic nitrate-reducing system. It was first identified as a ferredoxin-dependent chloroplast enzyme which catalyzes the 6-electron reduction of nitrite to ammonia. Usual assay involves sodium dithionite as reductant and either ferredoxin or its artificial substitute, methyl viologen, as electron carrier. Enzymatic activity can be best followed by measuring colorimetrically the rate of disappearance of nitrite. The reaction is run in open test tubes. The reduced methyl viologen assay follows the nitrite reductase activity of a purified preparation by measuring colorimetrically at 604 nm the rate of nitrite-dependent oxidation of reduced methyl viologen (MVH), which can be prepared with H2 and platinum asbestos. The NADPH assay method is based on the use of NADPH and ferredoxin–NADP reductase as electron-donor system to reduce ferredoxin. It follows nitrite reductase activity by measuring colorimetrically the rate of disappearance of nitrite. Nitrite reductases from spinach, calabash, Curcubita pepo, and Chlorella have been purified to homogeneity. The purified enzyme can be stored in the deep-freeze for several months with no loss in activity.