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PubMed2004

Inhibition of vanadium chloroperoxidase from the fungus Curvularia inaequalis by hydroxylamine, hydrazine and azide and inactivation by phosphate.

The first detailed inhibition study of recombinant vanadium chloroperoxidase (rVCPO) using hydroxylamine, hydrazine and azide has been carried out. Hydroxylamine inhibits rVCPO both competitively and uncompetitively. The competitive inhibition constant K(ic) and the uncompetitive inhibition constant K(iu) see are 40 and 80 microM, respectively. The kinetic data suggest that rVCPO may form a hydroxylamido complex, hydroxylamine also seems to react with the peroxovanadate complex during turnover. The kinetic data show that the type of inhibition for hydrazine and azide is uncompetitive with the uncompetitive inhibition constant K(iu) of 350 microM and 50 nM, respectively, showing that in particular azide is a very potent inhibitor of this enzyme. Substitution of vanadate in the active site by phosphate also leads to inactivation of vanadium chloroperoxidase. However, the presence of H(2)O(2) clearly prevents the inactivation of the enzyme by phosphate. This shows that pervanadate is bound much more strongly to the enzyme than vanadate.

Azides↗
PubMed2001

Selective reaction of hydroxylamine with chromophore during the photocycle of pharaonis phoborhodopsin.

Phoborhodopsin (pR; also called sensory rhodopsin II, sRII) is a receptor of negative phototaxis of Halobacterium salinarum, and pharaonis phoborhodopsin (ppR; also pharaonis sensory rhodopsin II, psRII) is a corresponding protein of Natronobacterium pharaonis. These receptors contain retinal as a chromophore which binds to a lysine residue via Schiff base. This Schiff base can be cleaved with hydroxylamine to loose their color (bleaching). In dark, the bleaching rate of ppR was very slow whereas illumination accelerated considerably the bleaching rate. Addition of azide accelerated the decay of the M-intermediate while its formation (decay of the L-intermediate) is not affected. The bleaching rate of ppR under illumination was decreased by addition of azide. Essentially no reactivity with hydroxylamine under illumination was observed in the case of D75N mutant which lacks the M-intermediate in its photocycle. Moreover, we provided illumination by flashes to ppR in the presence of varying concentrations of azide to measure the bleaching rate per one flash. A good correlation was obtained between the rate and the mean residence time, MRT, which was calculated from flash photolysis data of the M-decay. These findings reveal that water-soluble hydroxylamine reacts selectively with the M-intermediate and its implication was discussed.

Archaeal Proteins↗
PubMed2001

Hydroxylamine-containing inhibitors of polyamine biosynthesis and impairment of colon cancer cell growth.

Polyamine synthesis (by the action of ornithine decarboxylase [ODC] and S-adenosylmethionine decarboxylase [SAMDC]) and polyamine content are high in colon cancer. In addition, colonic lumen is rich in polyamines synthesised by colonic microflora; for this reason, polyamine depletion in colon cancer may be a logical approach to impair growth of colon cancer cells. We evaluated highly specific and reportedly non-toxic hydroxylamine-containing inhibitors of ODC (1-aminooxy-3-aminopropane, APA) and SAMDC (S-(5'-deoxy-5'-adenosyl)-methylthioethyl-hydroxylamine, AMA) in human colon cancer cells (Caco-2 and HT-29) in culture. APA depleted ODC activity within 24 hr, more rapidly than did difluoromethylornithine. APA and AMA in combination (100 microM each) reduced ODC and SAMDC activities to undetectable levels within 24 hr and intracellular polyamines to 8-23% of control. The resulting growth arrest could be reversed only by twice as much spermidine as is physiologically present in the colonic lumen. In concentrations sufficient to deplete growth, APA and AMA were not toxic. Simultaneous treatment with APA, AMA, and 5-fluorouracil reduced colon cancer cell survival more potently than treatment with 5-fluorouracil alone. The hydroxylamine-containing ODC and SAMDC inhibitors APA and AMA are potent inhibitors of colon cancer cell proliferation and might be therapeutically promising in colon cancer.

Adenosylmethionine Decarboxylase↗
PubMed1999

Hydroxylamine blocks adenosine A1 receptor-mediated inhibition of synaptic transmission in rat hippocampus.

The nitric oxide donor hydroxylamine (NH2OH) induced a transient depression of the evoked synaptic potential recorded in the rat hippocampal CA1 region. This depression was abolished with an adenosine A1 antagonist, 8-cyclopentyltheophylline. In addition, hydroxylamine reversed adenosine A1 receptor-mediated inhibition of the evoked population spike, the fEPSP and the intracellularly recorded EPSP. The inhibitory modulation of adenosine A1 receptor activation by hydroxylamine suggests the presence of a potent endogenous regulatory site.

Animals↗
PubMed1999

Hydroxylamine blocks pre- but not postsynaptic adenosine A(1) receptor-mediated actions in rat hippocampus.

The commonly used nitric oxide donor, hydroxylamine (NH(2)OH), can block or reverse the inhibition of glutamatergic transmission by adenosine or an adenosine A(1) agonist in rat hippocampal slice. In these experiments, hydroxylamine did not affect the adenosine A(1) receptor-mediated depression of postsynaptic excitability. We conclude that hydroxylamine acts presynaptically to counter adenosine A(1) receptor-mediated inhibition of synaptic transmission.

Adenosine↗
PubMed1999

The inhibition of human cytomegalovirus (hCMV) protease by hydroxylamine derivatives.

Aryl hydroxylamine derivatives have been synthesised that are some of the most potent inhibitors of hCMV protease prepared to date (IC50 14-60 nM). Mass spectrometry studies indicate that oxazinone derived hydroxylamines inhibit the enzyme by acylation of Ser132 whereas non-oxazinone derived hydroxylamines appear to inhibit via formation of a sulfinanilide at Cys138.

Amino Acid Sequence↗
PubMed2003

Effect of hydroxylamine on photosystem II: reinvestigation of electron paramagnetic resonance characteristics reveals possible S state intermediates.

Previous work in many laboratories has established that hydroxylamine reduces the S(1) state of the water oxidizing complex (WOC) in one-electron steps. Significant levels of what can now be defined as the S(-1)* state are achieved by specific (concentration and incubation length) hydroxylamine treatments. This state has already been studied by electron paramagnetic resonance spectrometry (EPR), and unusual EPR signals were noted (for example, see Sivaraja, M., and Dismukes, G. C. (1988) Biochemistry 27, 3467-3475). We have now reinvestigated these initial experiments and confirmed many of the original observations. We then utilized more recent EPR markers for the S(0) and S(1) states to further explore the S(-1)* state. The broad radical "split" type EPR signal, produced by 200 K illumination of samples prepared to give a high yield of the S(-1)* state, is shown to most likely reflect a trapped intermediate state between S(-1)* and S(0)*, since samples where this signal is present can be warmed in the dark to produce S(0)*. The threshold for advancement from S(-1)* to S(0)* is near 200 K, as the yield of broad radical decreases and S(0)* multiline EPR signal increases with length of 200 K illumination. Advancement of S(0)* to S(1) is limited at 200 K, but S(1) can be restored by 273 K illumination. Illumination of these hydroxylamine-treated samples at temperatures below 77 K gives a second broad radical EPR signal. The line shape, decay, and other properties of this new radical signal suggest that it may arise from an interaction in the S(-2)* or lower S states, which are probably present in low yield in these samples. Illumination below 20 K of S(0)* state samples containing methanol, and therefore exhibiting the S(0) multiline signal, gives rise to a third broad radical with distinctive line shape. The characteristics of the three broad radicals are similar to those found from interactions between Y(Z)(*) and other S states. The evidence is presented that they do represent intermediate states in S state turnover. Further work is now needed to identify these radicals.

Electron Spin Resonance Spectroscopy↗
PubMedDate not supplied

TNT phytotransformation pathway characteristics in Arabidopsis: role of aromatic hydroxylamines.

Basic knowledge of the plant transformation pathways of TNT will aid phytoremediation design and assessment. While TNT transformation by plant metabolism has been demonstrated in previous studies, the presence and role of hydroxylamines in the transformation pathway has not been sufficiently understood. Hydroxylamines are unequivocally shown to be formed by plant transformation of TNT by two axenic plant systems (Arabidopsis thaliana and Catharanthusroseus). In addition, confirmation was obtained for conversion of these hydroxylamines to previously identified conjugates. Further characteristics of TNT transformation in Arabidopsis, an increasingly popular model system for genetic and biochemical studies of TNT transformation, were elucidated by [U-14C]TNT mass balance studies and metabolite feeding studies. These studies showed the rapid conversion of TNT to unextractable bound compounds by Arabidopsis seedlings in agreement with the green-liver model. Arabidopsis seedlings formed and transformed 4-substituted metabolites more efficiently than the 2-substituted metabolites. A qualitative kinetic rate analysis of the pathway was performed to propose rate-limiting steps in the pathway and theoretical schemes for improved rates are suggested.

Arabidopsis↗
PubMed2000

Surface-mediated reactions. 9. Selective oxidation of primary and secondary amines to hydroxylamines.

OXONE over silica gel or, in some cases, alumina has been found to oxidize the primary and secondary amines 3 selectively to the corresponding hydroxylamines 4, in either the presence or absence of a solvent. Treatment of Boc-protected L-lysine (6) under the latter conditions afforded hydroxylamine 7 in excellent yield. The trialkylamine 1a and pyridine (1b), in which selectivity is not an issue, were readily oxidized to the corresponding oxides 2 by OXONE over silica gel or alumina, as well as by (CH(3))(3)COOH over silica gel. Solvent-free oxidation assisted by microwave irradiation was more forcing, while still affording the hydroxylamines 4 selectively, and is the synthetic method of choice. The mechanistic aspects of these reactions are discussed.

Aluminum Oxide↗
PubMed1973

The distinction between gamma-glutamylhydroxamate synthetase and L-glutamine-hydroxylamine glutamyltransferase activities in rat tissues.

The formation of gamma-glutamylhydroxamate by homogenates under optimum assay condition showed an inconstancy in the ratios of the enzyme activities utilizing l-glutamate and ATP (gamma-glutamylhydroxamate synthetase) and l-glutamine and ADP (l-glutamine-hydroxylamine glutamyltransferase) in a number of normal and neoplastic rat tissues. Although gamma-glutamylhydroxamate synthetase activities in adult livers and kidneys were identical in males and females, l-glutamine-hydroxylamine glutamyltransferase activities in the organs of females were significantly lower. The developmental formations of the two activities in liver, kidney, brain and muscle were not simultaneous. The l-glutamine-hydroxylamine glutamyltransferase activity in foetal liver or neonatal kidney could be prematurely evoked by thyroxine, but the gamma-glutamylhydroxamate synthetase activity remained unchanged. Injections of cortisol also had dissimilar effects on the two activities in thymus and hepatomas. The discrepant tissue distribution, asynchronous developmental formation and differential response to several hormonal stimuli provide evidence in vivo that the two activities are not catalysed by the same protein.

Acyltransferases↗
PubMed2001

Engineered nonphosphorylating glyceraldehyde 3-phosphate dehydrogenase at position 268 binds hydroxylamine and hydrazine as acyl acceptors.

Nonphosphorylating nicotinamide adenine dinucleotide (phosphate)-dependent aldehyde dehydrogenases (ALDHs) catalyze the oxidation of aldehydes into either nonactivated acids or CoA-activated acids. The NADP-dependent nonphosphorylating glyceraldehyde 3-phosphate dehydrogenase (GAPN) belongs to the first subclass. It catalyzes the irreversible oxidation of glyceraldehyde 3-phosphate into 3-phosphoglycerate via a two step mechanism in which deacylation is rate-limiting. Recent studies on GAPN from Streptococcus mutans have shown that residue Glu268 plays an essential role only in the deacylation step [Marchal, S., Rahuel-Clermont, S. & Branlant, G. (2000) Biochemistry 39, 3327-3335]. The substitution of Glu268 by alanine or glutamine leads to mutants in which the attacking water molecule involved in the hydrolytic process is poorly activated. Activity can be restored by the presence of hydroxylamine and hydrazine. Neutral and protonated forms of both nucleophiles are recognized by the deacylating subsite of both mutants. pH rate profiles of deacylation show pK(a) values of 6.3 and 8.1 with hydroxylamine and hydrazine, respectively, which are those of the nucleophiles in solution. The increase in enzymatic rate is probably due to a high local concentration and not to a change of the chemical reactivity of both nucleophiles upon their binding within the active site of both mutants. The deacylation subsite of the wild-type also binds hydroxylamine and hydrazine but as inhibitors of the hydrolytic process and not as acyl acceptors. Altogether, the results point out the crucial role of the carboxyl group of Glu268 in preventing nucleophiles, other than water, from binding as efficient acyl acceptors. This may also explain why CoA-dependent ALDHs never possesses a glutamate residue at position 268.

Binding Sites↗
PubMed1999

Amyloid beta peptides do not form peptide-derived free radicals spontaneously, but can enhance metal-catalyzed oxidation of hydroxylamines to nitroxides.

Amyloid beta (Abeta) peptides play an important role in the pathogenesis of Alzheimer's disease. Free radical generation by Abeta peptides was suggested to be a key mechanism of their neurotoxicity. Reports that neurotoxic free radicals derived from Abeta-(1-40) and Abeta-(25-35) peptides react with the spin trap N-tert-butyl-alpha-phenylnitrone (PBN) to form a PBN/.Abeta peptide radical adduct with a specific triplet ESR signal assert that the peptide itself was the source of free radicals. We now report that three Abeta peptides, Abeta-(1-40), Abeta-(25-35), and Abeta-(40-1), do not yield radical adducts with PBN from the Oklahoma Medical Research Foundation (OMRF). In contrast to OMRF PBN, incubation of Sigma PBN in phosphate buffer without Abeta peptides produced a three-line ESR spectrum. It was shown that this nitroxide is di-tert-butylnitroxide and is formed in the Sigma PBN solution as a result of transition metal-catalyzed auto-oxidation of the respective hydroxylamine present as an impurity in the Sigma PBN. Under some conditions, incubation of PBN from Sigma with Abeta-(1-40) or Abeta-(25-35) can stimulate the formation of di-tert-butylnitroxide. It was shown that Abeta peptides enhanced oxidation of cyclic hydroxylamine 1-hydroxy-4-oxo-2,2,6, 6-tetramethylpiperidine (TEMPONE-H), which was strongly inhibited by the treatment of phosphate buffer with Chelex-100. It was shown that ferric and cupric ions are effective oxidants of TEMPONE-H. The data obtained allow us to conclude that under some conditions toxic Abeta peptides Abeta-(1-40) and Abeta-(25-35) enhance metal-catalyzed oxidation of hydroxylamine derivatives, but do not spontaneously form peptide-derived free radicals.

Amyloid beta-Peptides↗
PubMed1996

Adverse reactions to co-trimoxazole in HIV infection: a reappraisal of the glutathione-hydroxylamine hypothesis.

It is postulated that the unstable hydroxylamine metabolite of sulphamethoxazole is responsible for the adverse reactions to co-trimoxazole and in HIV infection systemic glutathione deficiency leads to a reduced capacity to counteract the hydroxylamine toxicity. This hypothesis has been investigated by studying the metabolism of sulphamethoxazole and assessing glutathione status in HIV infection in order to explore the modification of treatment. It is concluded that the toxicity of plasma sulphamethoxazole hydroxylamine is counteracted by normal glutathione concentrations as is the case in HIV-seropositive patients, but that increased oxidation within certain cells in HIV infected individuals may possibly give rise to increased concentrations of reactive intermediates of sulphamethoxazole. Sulphametrole and sulphamethoxazole have similar half-lives but are metabolized differently: in vivo no oxidised metabolites of sulphametrole could be detected. In a retrospective study the rate of adverse reactions to trimethoprim-sulphametrole appeared to be in the lower range of those reported for trimethoprim-sulphamethoxazole indicating that the combination of trimethoprim-sulphametrole may be more favourable. The ratio of trimethoprim:sulphonamide is 1:5, but in-vitro studies with Toxoplasma gondii indicate that because of the synergic effect of both agents the dose of sulphonamide is possibly unnecessarily high.

Anti-Infective Agents↗
PubMed1975

The covalent structure of collagen. The chymotrypsin, trypsin and hydroxylamine peptides derived from alpha2-CB4 of calf-skin collagen.

The cyanogen-bromide-derived peptide alpha2-CB4 from calf skin collagen, consisting of 321 amino acid residues, has been fragmented in order to obtain peptides suitable for automated sequential analysis. Digestion with chymotrypsin liberated six unique peptides consisting of 12, 17, 19, 54, 63 and 156 amino acid residues. Treatment of alpha2-CB4 with hydroxylamine yielded four peptides with 24, 87, 96 and 114 residues. No unspecific cleavage by hydroxylamine was encountered. All of the trypsin-derived peptides of alpha2-CB4 were isolated and characterized by their amino acid compositions. Most of the peptides isolated were ordered along the peptide chain of alpha2-CB4. Ordering of the peptides was greatly assisted by the isolation of double peptides from the chymotrypsin, trypsin and hydroxylamine-derived peptide mixtures.

Amino Acid Sequence↗
PubMed1989

Hydroxylamine dilates resistance blood vessels of the perfused rat kidney and mesentery.

Hydroxylamine (ED50 values, 47 +/- 8.9 nmol and 320 +/- 39 nmol) dilates resistance arterioles of the perfused noradrenaline-preconstricted rat kidney and mesentery. In this respect hydroxylamine was approximately 63x and 320x less potent than acetylcholine (ACh) and 15x and 128x less potent than nitroprusside in the two perfused organs studied. The vasodilator effect of hydroxylamine (unlike that of ACh) was unaffected by CHAPS de-endothelialization suggesting that its effect is independent of endothelium-derived relaxing factor (EDRF).

Acetylcholine↗
PubMed2002

Hydroxylamine reductase activity of the hybrid cluster protein from Escherichia coli.

The hybrid cluster protein (HCP; formerly termed the prismane protein) has been extensively studied due to its unique spectroscopic properties. Although the structural and spectroscopic characteristics are well defined, its enzymatic function, up to this point, has remained unidentified. While it was proposed that HCP acts in some step of nitrogen metabolism, a specific role for this enzyme remained unknown. Recent studies of HCP purified from Escherichia coli have identified a novel hydroxylamine reductase activity. These data reveal the ability of HCP to reduce hydroxylamine in vitro to form NH(3) and H(2)O. Further biochemical analyses were completed in order to determine the effects of various electron donors, different pH levels, and the presence of CN(-) on in vitro hydroxylamine reduction.

Absorption↗
PubMed2005

The hydroxylamine reaction of sensory rhodopsin II: light-induced conformational alterations with C13=C14 nonisomerizable pigment.

Sensory rhodopsin II, a repellent phototaxis receptor from Natronomonas (Natronobacterium) pharaonis (NpSRII), forms a complex with its cognate transducer (NpHtrII). In micelles the two proteins form a 1:1 heterodimer, whereas in membranes they assemble to a 2:2 complex. Similarly to other retinal proteins, sensory rhodopsin II undergoes a bleaching reaction with hydroxylamine in the dark which is markedly catalyzed by light. The reaction involves cleavage of the protonated Schiff base bond which covalently connects the retinal chromophore to the protein. The light acceleration reflects protein conformation alterations, at least in the retinal binding site, and thus allows for detection of these changes in various conditions. In this work we have followed the hydroxylamine reaction at different temperatures with and without the cognate transducer. We have found that light irradiation reduces the activation energy of the hydroxylamine reaction as well as the frequency factor. A similar effect was found previously for bacteriorhodopsin. The interaction with the transducer altered the light effect both in detergent and membranes. The transducer interaction decreased the apparent light effect on the energy of activation and the frequency factor in detergent but increased it in membranes. In addition, we have employed an artificial pigment derived from a retinal analog in which the critical C13=C14 double bond is locked by a rigid ring structure preventing its isomerization. We have observed light enhancement of the reaction rate and reduction of the energy of activation as well as the frequency factor, despite the fact that this pigment does not experience C13=C14 double bond isomerization. It is suggested that retinal excited state polarization caused by light absorption of the "locked" pigment polarizes the protein and triggers relatively long-lived protein conformational alterations.

Carbon↗
PubMed1975

Excitability of crayfish giant axons in sodium-free external media containing hydrazinium, hydroxylamine, or guanidinium ions.

Giant axons of crayfish were excitable in sodium-free external media containing hydrazinium, hydroxylamine, or guanidinium ions. Action potentials in these solutions were slightly smaller in size and a little longer in duration than those in standard Harreveld's solution. The resting potential was not affected in hydrazine or in hydroxylamine saline, but decreased in gaunidine saline. The membrane potential at the peak of the spike (V) was plotted against the univalent cation concentrations in the external medium. The relationship could be expressed by an equation: V = VO + (RT/F) ln ([Na] + alpha[C]), where VO and alpha are constants and [Na] and [C] are concentrations of sodium ions and the tested cations, respectively. The parameter alpha was considered as an indicator to express the ability of substitution of the cation for sodium ion. The order of the ability of the substitution was Hydroxylamine greater than Hydrazinium greater than Guanidinium greater than Choline.

Action Potentials↗