Nitrate reductase inactive

It was important to identify mutant strains with defects in nitrogenase similar to the defect observed in nitrate reductase in the Nit-1 mutant strain of N. crassa (6). It was postulated that such strains would be able to synthesize active component II and an inactive component I that could be activated in vitro by the molybdenum cofactor. Cell-free... 

The nitrates and nitrites are best absorbed through the mucous membrane lining the mouth and nose. Therefore, they are usually administered sublingually or buccally. They may also be inhaled. When administered by these routes, the active ingredient is absorbed into the venous circulation and travels via the vena cava to the heart, aorta, and coronary arteries. If these agents are taken orally, they are metabolized to inactive compounds by nitrate reductase in the liver. 

A reactivation of an inactive nitrate reductase apoenzyme extracted from molybdenum-deficient plants can be achieved by the addition of acid-treated nitrate reductase or by addition of phosphate buffer washes of nitrate reductase absorbed on AMP-Sepharose. The acid treatment or phosphate wash apparently produced a molybdenum-containing complex which was responsible for reactivation of the apoenzyme. The complex had a molecular weight of less than 3 x 10 (Notton and Hewitt, 1971 Rucklidgee/< /., 1976). These reports clearly demonstrate the requirement for molybdenum for nitrate reduction however, the role of the metal in the reduction process is not completely resolved. 

A similar situation may occur in higher plants as Notton et al. (1974) and Rucklidge et al. (1976) have demonstrated that inactive nitrate reductase is produced in molybdenum-deficient plants. 

The conversion in vitro of the active form of Chlorella nitrate reductase into the inactive form depends on its reduction by NAD(P)H, and is reversible by reoxidation with ferri-cyanide. Inactivation by NADH requires the first moiety of the complex to be active and proceeds much faster at high pH or when ADP at low concentration (0 3 mM) is simultaneously present. This synergistic effect is quite specific for NADH and ADP. Nitiate, as well as several of its competitive inhibitors, completely prevents and even reverses inactivation by NADH and ADP. In fact, Vennesland and co-workers have demonstrated the presence of cyanide in the in vivo inactivated enzyme by overnight incubation with nitrate and phosphate. ... 

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