Nitrite formation from hydroxylamine

Amarger, N., and Alexander, M. (1968). Nitrite formation from hydroxylamine and oximes by Pseudomonas aeruginosa. ]. Bacteriol. 95, 1651-1657. 

Fig. 3.6. A schematic presentation of nitrite formation from hydroxylamine in the cell of Alcaligenes faecalis. Circled numbers 1, ammonia monooxygenase 2, pyruvic oxime...

Figure 7. Nitrite formation from hydroxylamine. Reaction mixture contained in 3 mL 50 mM phosphate buffer pH 7.8 1 fjjnol of NH OH chloroplasts with 75 /xg of chlorophyll and where indicated 6.6 /aM paraquat 50 units SOD. Illuminated at 275 Wm at 22°C. Key control, plus paraquat. A plus SOD, and plus paraquat and SOD, A (72).

Given that hydroxylamine reacts rapidly with heme proteins and other oxidants to produce NO [53], the hydrolysis of hydroxyurea to hydroxylamine also provides an alternative mechanism of NO formation from hydroxyurea, potentially compatible with the observed clinical increases in NO metabolites during hydroxyurea therapy. Incubation of hydroxyurea with human blood in the presence of urease results in the formation of HbNO [122]. This reaction also produces metHb and the NO metabolites nitrite and nitrate and time course studies show that the HbNO forms quickly and reaches a peak after 15 min [122]. Consistent with earlier reports, the incubation ofhy-droxyurea (10 mM) and blood in the absence of urease or with heat-denatured urease fails to produce HbNO over 2 h and suggests that HbNO formation occurs through the reactions of hemoglobin and hydroxylamine, formed by the urease-mediated hydrolysis of hydroxyurea [122]. Significantly, these results confirm that the kinetics of HbNO formation from the direct reactions of hydroxyurea with any blood component occur too slowly to account for the observed in vivo increase in HbNO and focus future work on the hydrolytic metabolism of hydroxyurea. 

It is now well established that hydroxylamine is an intermediate, the oxygen atom being derived from dioxygen (equation 93).1539 The formation of hydroxylamine and its subsequent oxidation to nitrite are affected differently by various inhibitors, while certain inhibitors cause an accumulation of hydroxylamine. This suggests that the two processes are independent. The presence of dioxygen is essential for hydroxylamine to be oxidized to nitrite, otherwise N20 and NO are formed. 

The effect of monuron (10 M) on the ability of paraquat to promote the formation of nitrite from hydroxylamine in isolated chloroplasts. For further details see legend to Figure 7, from Youngman jet al. (32)... 

Methods of formation of IV-nitrosamines from secondary amines have been reviewed. The most widely used reagent is sodium nitrite in an aqueous acidic medium others include nitrosyl chloride, nitrogen oxides and nitrite esters. Fremy s stdt (S03")2N0-] reacts with hydroxylamine in the presence of secondary amines to give A -nitrosamines, or, in the presence of an excess of hydroxylamine, tetrazenes RaNN sNNR . The nitrosating agent derived from hydroxylamine and Fremy s salt is suggested to be the anion (S03")2N0N0. ... 

The pure, anhydrous nitrite is not hygroscopic, but as usually prepared the substance is a very deliquescent, crystalline solid, its aqueous solution having a slight alkaline reaction. At 15-5° C. the solubility is 300 grams per 100 grams of water.11 The heat of formation in aqueous solution from the elements is 88-9 Cal.12 The products of electrolytic reduction are hyponitrite, ammonia, and hydroxylamine. 

N-Nitrosation of oximes by nitrosyl halides or nitrite esters often results in the formation of N-nitrimines, R R C=NN02, these compounds being formed by rearrangement of the initial adducts. N-Amination of oximes by chloramine or by hydroxylamine-O-sulfonic acid can result in the formation of diazo compounds (Scheme 28). The reaction, known as the Forster reaction, has been used for the preparation of aryldiazoalkanes, although better methods are usually available. Diazo ketones of the general formula (49) have also been prepared by this method from the oximes. "... 

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