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Results for “Hydroxylamines”

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At least 991 records · Page 55Linked to original sources
PubMed1985

Studies on the photoactivation of the water-oxidizing enzyme : I. Processes limiting photoactivation in hydroxylamine-extracted leaf segments.

In weak yet optimal light intensity, complete photoactivation of the water-oxidizing enzyme in NH(2)OH-extracted wheat (Triticum aestivum, var Oasis) leaf segments could be obtained only after long dark preincubation. Photoactivation was not affected by ethylenediaminetetraacetate or inhibitors of photophosphorylation and protein synthesis, but was partially inhibited by a divalent cation ionophore. Complete photoactivation required ligation of approximately 4 Mn by the water oxidizing enzyme.WITHOUT DARK PREINCUBATION, PHOTOSYSTEM II (PSII) WAS SUSCEPTIBLE TO WEAK LIGHT PHOTOINHIBITION RESULTING IN: (a) 50% maximum decrease in photooxidation of artificial electron donors by PSII: (b) increased times for the variable fluorescence rise (with 3-(3,4-dichlorophenyl)-1,1-dimethyl urea): (c) abolishment of photoactivation: and (d) the imposition of sensitivity to inhibitors of photophosphorylation and 70S but not 80S protein synthesis on subsequent light-dependent recovery from photoinhibition and recovery of O(2) evolution. Decrease in susceptibility to photoinhibition and increase in rates of photoactivation resulting from dark preincubations proved closely correlated. Neither protein synthesis nor increases in abundances of thylakoid Mn(2+) and Ca(2+) were required for escape from photoinhibition. However, photoactivation of the wateroxidizing enzyme in NH(2)OH-extracted Chlamydomonas occurred in absence of dark preincubation and protein synthesis. Results are discussed in the context of disassembly/reassembly/resynthesis of specific PSII polypeptides.

Journal Article↗
PubMed1986

Characterization of the Reversible Inactivation of Ankistrodesmus braunii Nitrate Reductase by Hydroxylamine.

The photoreversible nature of the regulation of nitrate reductase is one of the most interesting features of this enzyme. As well as other chemicals, NH(2)OH reversibly inactivates the reduced form of nitrate reductase from Ankistrodesmus braunii. From the partial activities of the enzyme, only terminal nitrate reductase is affected by NH(2)OH. To demonstrate that the terminal activity was readily inactivted by NH(2)OH, the necessary reductants of the terminal part of the enzyme had to be cleared of dithionite since this compound reacts chemically with NH(2)OH. Photoreduced flavins and electrochemically reduced methyl viologen sustain very effective inactivation of terminal nitrate reductase activity, even if the enzyme was previously deprived of its NADH-dehydrogenase activity. The early inhibition of nitrate reductase by NH(2)OH appears to be competitive versus NO(3) (-). Since NO(3) (-), as well as cyanate, carbamyl phosphate and azide (competitive inhibitors of nitrate reductase versus NO(3) (-)), protect the enzyme from NH(2)OH inactivation, it is suggested that NH(2)OH binds to the nitrate active site. The NH(2)OH-inactivated enzyme was photoreactivated in the presence of flavins, although slower than when the enzyme was previously inactivated with CN(-). NH(2)OH and NADH concentrations required for full inactivation of nitrate reductase appear to be low enough to potentially consider this inactivation process of physiological significance.

Journal Article↗
PubMed1996

Mutagenesis of hydroxylamine oxidoreductase in Nitrosomonas europaea by transformation and recombination.

Mutagenesis of Nitrosomonas europaea was achieved by electroporation and recombination. To demonstrate this, an aminoglycoside 3'-phosphotransferase (kan) gene was specifically inserted into each of the three gene copies of hao individually. Southern hybridizations and PCR analysis showed the incorporation of the kan gene at the chosen genetic loci. The isolation of mutant strains was achieved in 7 to 14 days when the strains were grown on solid medium. The induced mutations were stable even in the absence of kanamycin-selective pressure for periods of up to 45 days in culture. The mutant strains did not show an observable phenotype different from that of the wild type when grown under the same conditions.

Base Sequence↗
PubMed1980

Mechanism of hydroxylamine mutagenesis: an infrared study of the association in non-polar solutions of 5-methyl-N4-hydroxycytosines.

An infrared spectroscopic study has been made of the structure and self-association of 1,5-dimethyl-N4-hydroxycytosine and 1,5-dimethyl-N4-methoxycytosine in several non-polar solvents as a function of concentration and temperature. Both compounds are predominantly in the imino form, and the overall results point to the existence of an intramolecular hydrogen bond between the ring N(3) hydrogen and the oxygen on the exocyclic N4, as previously found in the solid state. Furthermore, 1,5-dimethy-N4-hydroxycytosine forms linear associates in solution via hydrogen bonding, of the form N4-OH ... O=C2, with thermodynamic parameters delta H = -2.8 kcal/mol, delta S = -2.7 cal/deg . mol. As anticipated, the N4-methoxy derivatives does not form such associates. Neither of the compounds exhibits detectable association by hydrogen bonding with the potentially complementary 9-ethytl-adenine. Both compounds are also predominantly in the imino form in the gas phase.

5-Methylcytosine↗
PubMed1965

STUDIES ON THE OXIDATION OF AMMONIA BY NITROSOMONAS.

1. Free-energy calculations for pH7 showed that the oxidation of ammonia to hydroxylamine is endergonic and that the oxidations of hydroxylamine to nitrite and hydrazine to nitrogen are exergonic. It is suggested that the oxidation of ammonia requires the expenditure of energy. 2. The anaerobic dehydrogenation of hydrazine to nitrogen by extracts of the autotrophic nitrifying micro-organism, Nitrosomonas, in the presence of methylene blue as electron acceptor, was less rapid than the anaerobic dehydrogenation of hydroxylamine to nitric oxide. The inhibition by hydrazine of the dehydrogenation of hydroxylamine was attributed to substrate competition. 3. Whole cells in air did not produce nitrite from hydrazine. They produced nitrite from low concentrations of hydroxylamine more rapidly than from equimolar concentrations of ammonia; this result is consistent if hydroxylamine is an intermediate of the oxidation of ammonia. 4. The production of nitrite from hydroxylamine by whole cells was slightly inhibited by hydrazine, but the production of nitrite from ammonia was greatly inhibited and small amounts of hydroxylamine were formed. These results suggested that the dehydrogenation of hydroxylamine supplied energy required for the oxidation of ammonia and that hydroxylamine appeared because the energy production was replaced by that of the dehydrogenation of hydrazine. 5. The oxidation of hydroxylamine by whole cells was not inhibited by thiourea, but micromolar concentrations of the metal-binding agent markedly inhibited the oxidation of ammonia to hydroxylamine, suggesting that the oxidation of ammonia involved copper. A possible mechanism for the activation of ammonia is suggested.

Ammonia↗
PubMed1999

N-oxygenation of amphetamine and methamphetamine by the human flavin-containing monooxygenase (form 3): role in bioactivation and detoxication.

(+)- And (-)-amphetamine and methamphetamine were N-oxygenated by the cDNA expressed adult human flavin-containing monooxygenase form 3 (FMO3), their corresponding hydroxylamines. Two major polymorphic forms of human FMO3 were studied, and the results suggested preferential N-oxygenation by only one of the two enzymes. Chemically synthesized (+/-)-amphetamine hydroxylamine was also a substrate for the human FMO3 and it was converted to phenylpropanone oxime with a stereoselectivity ratio of trans/cis of 5:1. Human FMO3 also N-oxygenated methamphetamine to produce methamphetamine hydroxylamine. Methamphetamine hydroxylamine was also N-oxygenated by human FMO3, and the ultimate product observed was phenylpropanone. For amphetamine hydroxylamine, studies of the biochemical mechanism of product formation were consistent with the production of an N, N-dioxygenated intermediate that lead to phenylpropanone oxime. This was supported by the observation that alpha-deutero (+/-)-amphetamine hydroxylamine gave an inverse kinetic isotope effect on product formation in the presence of human FMO3. For methamphetamine, the data were consistent with a mechanism of human FMO3-mediated N,N-dioxygenation but the immediate product, a nitrone, rapidly hydrolyzed to phenylpropanone. The pharmacological activity of amphetamine hydroxylamine, phenylpropanone oxime, and methamphetamine hydroxylamine were examined for effects at the human dopamine, serotonin, and norepinephrine transporters. Amphetamine hydroxylamine and methamphetamine hydroxylamine were apparent substrates for the human biogenic amine transporters but phenylpropanone oxime was not. Presumably, phenylpropanone oxime or nitrone formation from amphetamine and methamphetamine, respectively, represents a detoxication process. Because of the potential toxic nature of amphetamine hydroxylamine and methamphetamine hydroxylamine metabolites and the polymorphic nature of N-oxygenation, human FMO3-mediated metabolism of amphetamine or methamphetamine may have clinical consequences.

Amphetamine↗