Phone: 49 Fax: 49 E-mail: ed. Received Jul 1; Accepted Oct
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Phone: 49 Fax: 49 E-mail: ed. Received Jul 1; Accepted Oct Abstract 3-Hydroxylaminophenol mutase from Ralstonia eutropha JMP is involved in the degradative pathway of 3-nitrophenol, in which it catalyzes the conversion of 3-hydroxylaminophenol to aminohydroquinone.
To show that the reaction was really catalyzed by a single enzyme without the release of intermediates, the corresponding protein was purified to apparent homogeneity from an extract of cells grown on 3-nitrophenol as the nitrogen source and succinate as the carbon and energy source. The pI was determined to be at pH 4. In a database search, the NH2-terminal amino acid sequence of the undigested protein and of two internal sequences of 3-hydroxylaminophenol mutase were found to be most similar to those of glutamine synthetases from different species.
Hydroxylaminobenzene, 4-hydroxylaminotoluene, and 2-chlorohydroxylaminophenol, but not 4-hydroxylaminobenzoate, can also serve as substrates for the enzyme. The enzyme requires no oxygen or added cofactors for its reaction, which suggests an enzymatic mechanism analogous to the acid-catalyzed Bamberger rearrangement. The recognition that synthetic nitroaromatic compounds are environmental hazards has led to a considerable amount of research on their biodegradation for reviews, see references 18 , 21 , 32 , 47 , and As a result, a variety of novel enzymatic mechanisms for the degradation or transformation of nitroarenes have been discovered.
Oxidative elimination of the nitro group as nitrite seems to be a key reaction in the catabolism of many mononitroaromatic and some dinitroaromatic compounds In general, the electron-withdrawing character of the nitro group favors biological reduction, giving rise to ring hydrogenation 28 , 29 , 54 , 55 or transformation of the nitro group to either nitroso, hydroxylamino, or amino derivatives 47 , Each of these products can be subjected to further transformation or mineralization Recent evidence suggests that the hydroxylaminoaromatic compounds are key intermediates in a variety of metabolic pathways of mononitroaromatic compounds.
For example, an enzymatic rearrangement of aromatic hydroxylamines and hydroxamic acids to their corresponding ortho-aminophenol derivatives was observed in rabbit liver 6 and rat liver homogenates In the latter report, a hepatic isomerase-catalyzed mechanism that corresponded to the acid-catalyzed chemical reaction formerly described by Bamberger was proposed 3. Furthermore, Corbett and Corbett showed that a yeast cometabolized 4-chloronitrobenzene via 4-chlorohydroxylaminobenzene to 2-hydroxychloroaniline and 4-aminophenol In all these studies, the described rearrangement reactions were rather nonspecific, since the aminophenolic compounds were not the only products formed from aromatic hydroxylamines or hydroxamic acids.
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Kazrashicage Bamberger rearrangement Reproduced material should be attributed as follows: Phenol and its chemical derivatives are essential for production of polycarbonates, epoxies, Bakelite, nylon, detergents, herbicides such as phenoxy herbicides, and numerous pharmaceutical drugs. Guanamines are closely related to melamine, except with one amino substituent replaced by an organic group. Reaction mechanism The mechanism of the Bamberger rearrangement proceeds from the monoprotonation of N-phenylhydroxylamine 1. Wallach rearrangement topic The Wallach rearrangement, also named Wallach transformation, is a name reaction in the organic chemistry.