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PubMed1986

Seed dormancy in red rice : v. Response to azide, hydroxylamine, and cyanide.

The activity of NaN(3) (0.5 millimolar), hydroxylamine-HCl (10-18 millimolar), and potassium cyanide (1 millimolar) as dormancy-breaking agents of dehulled red rice (Oryza sativa) is pH-dependent such that medium pH values favoring formation of the uncharged chemical species resulted in the highest germination percentages. There was no promotive effect of pH itself in the range of 3 to 10. The minimum contact times for maximum response (>/=90% germination) to NaN(3), KCN, and NH(2)OH-HCl are 8 hours at pH 4, 24 hours at pH 8, and 72 hours at pH 6 or 7, respectively, for exposure commencing at the start of imbibition. Dehulled seeds, imbibed first in water, show only slightly reduced germination when subsequently transferred to solutions of dormancy-breaking chemicals.Intact seeds remain dormant in the presence of NaN(3), KCN, or NH(2)OH-HCl unless partially dry-afterripened. The pH dependence of these chemicals is reduced in intact, afterripening seeds.

Journal Article↗

PubMed1998

Application of a fine thread beam to the structure analysis of a hemihedrally twinned crystal of hydroxylamine oxidoreductase.

Accurate diffraction intensity data have been collected from a twinned P6(3) crystal of the 24-haem protein hydroxylamine oxidoreductase, from a nitrifying chemoautotrophic bacterium Nitrosomonas europaea, using synchrotron radiation at station BL6A of the Photon Factory. Estimation of the twinning fraction and deconvoluted intensity data, including native and heavy-atom derivative data, gave an improved Patterson function. Four diffraction data sets were collected from one crystal and an estimation of the twinning fraction to confirm the phenomena was undertaken. The successfully detwinned data sets were utilized in the structure analysis of the present enzyme. The mechanism of twinned-crystal formation is also discussed.

Journal Article↗

PubMed1983

Hydroxylamine mutagenesis: observation of inverted Watson-Crick base-pairing between N4-methoxycytosine and adenine with the aid of natural-abundance high-resolution 15N NMR spectroscopy.

Natural-abundance high-resolution 15N NMR spectra have been recorded for 1-methyl-N4-methoxycytosine (the product of reaction of 1-methylcytosine with the mutagen methoxyamine), 2',3',5'-tri-O-methyladenosine, and a 1:1 mixture of the two, all in chloroform solution. The spectra were obtained by application of a sequence of impulses of the type referred to as insensitive nuclear enhancement by polarization transfer (INEPT). Assignments of all the nitrogen resonances were based on nitrogen-proton coupling constants and literature data. Analysis of the 15N chemical shifts demonstrated the formation of base pairs with hydrogen bonds involving the ring N(1) and an N6-H of adenine, and the N(3)-H and C(2) = O of N4-methoxycytosine, viz. N(1) . H-N(3) and N6-H . O2 = C. The hydrogen-bond-stabilized complex formed thus involves an inverse type of Watson-Crick base-pairing. The data excluded formation of Hoogsteen-type base-pairing. The results are considered in relation to hydroxylamine and methoxyamine mutagenesis, to types of base-pairing at the monomer and polymer levels, and to interpretations of 15N NMR spectra of heterocyclic rings in general.

Adenine↗

PubMed1983

Heme P460 of hydroxylamine oxidoreductase of Nitrosomonas. Reaction with CO and H2O2.

Hydroxylamine oxidoreductase (HAO) of Nitrosomonas catalyzes the dehydrogenation of NH2OH and subsequent addition of oxygen to form nitrite. HAO contains c hemes and the CO-binding heme P460 in a 7:1 ratio; dehydrogenation of NH2OH involves passage of electrons to P460 and then c hemes. We now report that electrons rapidly pass from c hemes of HAO to the P460 center and then to H2O2. This conclusion is supported by (a) inhibition of c heme oxidation with CO and (b) loss of H2O2-oxidizability of ferrous c hemes following specific destruction of heme P460. Reaction of ferrous P460 with H2O2 is rate-limiting. Activation of dioxygen for N-oxidation by ferrous HAO may involve the two-electron reduction of O2 by P460. The reaction of ferrous HAO with H2O2 was studied as it may reveal aspects of the mechanism of activation of dioxygen. Reaction of ferrous heme P460 with CO is slow and with low affinity as compared with other hemoproteins. Values for reaction of CO with enzyme were: k1, 1.1 X 10(-3) M-1 s-1 and Kd, 12 microM.

Carbon Monoxide↗

PubMed2006

Detection of a new N-oxidized metabolite of flutamide, N-[4-nitro-3-(trifluoromethyl)phenyl]hydroxylamine, in human liver microsomes and urine of prostate cancer patients.

Flutamide (2-methyl-N-[4-nitro-3-(trifluoromethyl)phenyl]-propanamide), a nonsteroidal antiandrogen, is used in the treatment of prostate cancer but is occasionally associated with hepatic dysfunction. In the present study, the metabolism of flutamide including the formation of the possible reactive toxic metabolites was investigated using human liver microsomes and 10 isoforms of recombinant human cytochrome P450 (P450). 2-Hydroxyflutamide (OH-flutamide) and 4-nitro-3-(trifluoromethyl)phenylamine (FLU-1) were the main products of flutamide metabolism in human liver microsomes. The formation of OH-flutamide was markedly inhibited by ellipticine, an inhibitor of CYP1A1/1A2, and was mainly catalyzed by the recombinant CYP1A2. FLU-1 was also produced from OH-flutamide, but its metabolic rate was much less than that from flutamide. An inhibitor of carboxylesterase, bis-(p-nitrophenyl)phosphoric acid, completely inhibited the formation of FLU-1 from flutamide in human liver microsomes. A new metabolite, N-[4-nitro-3-(trifluoromethyl)phenyl]hydroxylamine (FLU-1-N-OH), was detected as a product of the reaction of FLU-1 with human liver microsomes and identified by comparison with the synthetic standard. The formation of FLU-1-N-OH was markedly inhibited by the addition of miconazole, an inhibitor of CYP3A4, and was mediated by recombinant CYP3A4. Furthermore, FLU-1-N-OH was detected mostly as the conjugates (glucuronide/sulfate) in the urine of prostate cancer patients collected for 3 h after treatment with flutamide. The formation of FLU-1-N-OH, however, did not differ between patients with and without abnormalities of hepatic functions among a total of 29 patients. The lack of an apparent association of the urinary excretion of FLU-1-N-OH and hepatic disorder may suggest the involvement of an additional unknown factor in the mechanisms of flutamide hepatotoxicity.

Androgen Antagonists↗

PubMed2000

Physical map location of the multicopy genes coding for ammonia monooxygenase and hydroxylamine oxidoreductase in the ammonia-oxidizing bacterium Nitrosomonas sp. strain ENI-11.

Pulsed-field gel electrophoresis of PmeI digests of the Nitrosomonas sp. strain ENI-11 chromosome produced four bands ranging from 1,200 to 480 kb in size. Southern hybridizations suggested that a 487-kb PmeI fragment contained two copies of the amoCAB genes, coding for ammonia monooxygenase (designated amoCAB(1) and amoCAB(2)), and three copies of the hao gene, coding for hydroxylamine oxidoreductase (hao(1), hao(2), and hao(3)). In this DNA fragment, amoCAB(1) and amoCAB(2) were about 390 kb apart, while hao(1), hao(2), and hao(3) were separated by at least about 100 kb from each other. Interestingly, hao(1) and hao(2) were located relatively close to amoCAB(1) and amoCAB(2), respectively. DNA sequence analysis revealed that hao(1) and hao(2) shared 160 identical nucleotides immediately upstream of each translation initiation codon. However, hao(3) showed only 30% nucleotide identity in the 160-bp corresponding region.

Chromosome Mapping↗

PubMed1989

Metabolism of procainamide to the cytotoxic hydroxylamine by neutrophils activated in vitro.

An almost universal side effect of long-term therapy with procainamide is the appearance of serum autoantibodies and less frequently a syndrome resembling lupus erythematosus. Previous studies demonstrated that procainamide-hydroxylamine (PAHA), a metabolite generated by hepatic mixed function oxidases, was highly toxic to dividing cells, but evidence that PAHA could be formed in the circulation was lacking. This study examines the capacity of neutrophils to metabolize procainamide to reactive forms. Neutrophils activated with opsonized zymosan were cytotoxic only if procainamide was present, whereas N-acetyl procainamide, which does not induce autoimmunity, was inert in this bioassay. PAHA was detected by HPLC in the extracellular medium if ascorbic acid was present. Generation of PAHA and cytotoxic procainamide metabolites was inhibited by NaN3 and catalase but not by superoxide dismutase, indicating that H2O2 and myeloperoxidase were involved. Nonactivated neutrophils and neutrophils from patients with chronic granulomatous disease did not generate cytotoxic PAHA, demonstrating that H2O2 was derived from the respiratory burst accompanying neutrophil activation. These conclusions were supported by results of a cell-free system in which neutrophils were replaced by myeloperoxidase and H2O2 or an H2O2 generating system. These studies demonstrate the capacity of neutrophils to mediate metabolism of procainamide and establish the role of myeloperoxidase released during degranulation and H2O2 derived from the respiratory burst in the direct cooxidation of procainamide to PAHA. The profound biologic activity of this metabolite and its possible generation within lymphoid compartments implicate this process in the induction of autoimmunity by procainamide.

Adult↗

PubMed2000

Mutational analysis of the multicopy hao gene coding for hydroxylamine oxidoreductase in Nitrosomonas sp. strain ENI-11.

The ammonia-oxidizing bacterium Nitrosomonas sp. strain ENI-11 contains three copies of the hao gene (hao1, hao2, and hao3) coding for hydroxylamine oxidoreductase (HAO). Three single mutants (hao1::kan, hao2::kan, or hao3::kan) had 68 to 75% of the wild-type growth rate and 58 to 89% of the wild-type HAO activity when grown under the same conditions. A double mutant (hao1::kan and hao3::amp) also had 68% of the wild-type growth and 37% of the wild-type HAO activity.

DNA Mutational Analysis↗

PubMed2004

Development of a headspace GC/MS analysis for carbonyl compounds (aldehydes and ketones) in household products after derivatization with o-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine.

Carbonyl compounds (aldehydes and ketones) are suspected to be among the chemical compounds responsible for Sick Building Syndrome and Multiple Chemical Sensitivities. A headspace gas chromatography/mass spectrometry (GC/MS) analysis for these compounds was developed using derivatization of the compounds into volatile derivatives with o-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine (PFBOA). For GC/MS detection, two ionization modes including electron impact ionization (EI) and negative chemical ionization (NCI) were compared. The NCI mode seemed to be better because of its higher selectivity and sensitivity. This headspace GC/MS (NCI mode) was employed as analysis for aldehydes and ketones in materials (fiber products, adhesives, and printed materials). Formaldehyde was detected in the range of N.D. (not detected) to 39 microg/g; acetaldehyde, N.D. to 4.1 microg/g; propionaldehyde, N.D. to 1.0 microg/g; n-butyraldehyde, N.D. to 0.10 microg/g; and acetone, N.D. to 3.1 microg/g in the samples analyzed.

Journal Article↗

PubMed1988

Anticonvulsive effect of 2-hydroxylamine-5-ethyl-5-sec-pentyl barbituric acid (HB-7) in two experimental models of epilepsy.

The effects of barbiturate HB-7 (2-hydroxylamine-5-ethyl-5-sec-pentylbarbituric acid) injected intraperitoneally compared to the effects of pentobarbital and/or phenobarbital were investigated in three series of experiments on cats: normal electrocorticogram (ECoG); pentylentetrazol-induced generalized paroxysmal ECoG; and paroxysmal ECoG activity induced by topical application of penicillin on the exposed cortical surface. In the first series, HB-7 led to the appearance of ECoG spindles of the same type as those elicited by pentobarbital. In the second series (pentylentetrazol-treated group), HB-7 increased the two thresholds: one associated with the appearance of isolated paroxysmal spike-wave complexes and the other corresponding to the appearance of generalized paroxysmal ECoG activity. In the third series, HB-7 led to an inhibition of penicillin spikes, both in the focus itself and in the other cortical areas where they propagated. The possibility for using HB-7 as an antiepileptic drug was discussed.

Animals↗

PubMed1993

Optical spectropotentiometric resolution of the hemes of hydroxylamine oxidoreductase. Heme quantitation and pH dependence of Em.

The hemes of hydroxylamine oxidoreductase (HAO) have been analyzed optically by potentiometric titrations using a low volume optically transparent thin layer electrochemical cell. The electrochemical behavior of the HAO monomeric unit has been interpreted by modeling the spectroelectrochemical data at several wavelengths to eight one-electron Nernst sites: seven c-type hemes and one P460 heme. Of the seven c-hemes, six show alpha-bands with absorption maxima at or near 553 nm. One c-heme has an alpha-band absorption maximum at 559 nm. The six c-553 hemes have midpoint potentials at pH 7.0 of +288, -10, -162, -192, -265 and -412 mV versus the normal hydrogen electrode (NHE). The c-559 heme has a midpoint potential (Em') at pH 7.0 of +11 mV versus NHE. The midpoint potential of the P460 heme is at -260 mV versus NHE at pH 7.0. In contrast, the midpoint potential for the P460 heme in another protein, cytochrome P460, from the same organism is -402 mV versus NHE at pH 7.0. Midpoint potentials of the c-hemes show little, if any, pH dependence over the range of pH 6-8. In contrast, Em' for the P460 heme changes with a slope of -60 mV/pH unit over the same range. Electrochemical isolation of the P460 heme at pH 8.0 led to the discovery of a broad spectroscopic feature centered near 740 nm that was assigned to the oxidized P460 heme. Changes in the spectroelectrochemical behavior of HAO after inactivation by H2O2 was almost exclusively restricted to the P460 heme of HAO. Both the 464-nm absorption band of the reduced P460 heme and the 740-nm band of the oxidized heme were no longer present. For the c-hemes, the only effect seems to be a slight shift in Em' for a single c-553 heme from -162 to -135 mV.

Cytochromes↗

PubMed1997

The hydroxylamine of sulfamethoxazole synergizes with FK506 and cyclosporin A, inhibiting T-cell proliferation.

We previously demonstrated the capacity of the hydroxylamine metabolite of sulfamethoxazole (SMX-HA) to inhibit mitogen-induced T-cell proliferation. We studied the interaction of SMX-HA with the immuno-suppressants cyclosporin A (CsA), FK506 and rapamycin. Human peripheral blood mononuclear leukocytes were treated with SMX-HA and combined in culture with CsA or FK506 or rapamycin. The cells were stimulated with phytohaemaglutinin, and phorbol myristate acetate and proliferation was determined by cellular uptake of 3H-thymidine. Using median-effect analysis and concentration reduction index calculations to assess immunosuppressive drug interactions, we produced synergistic immunosuppression by SMX-HA/CsA and SMX-HA/FK506. Concentration reductions at the 50% inhibitory level of over 46-fold and 64-fold with CsA and FK506, respectively, were observed with 25 microM SMX-HA, and this effect was not associated with reduced cell viability. SMX-HA failed to augment the suppressive capacity of rapamycin in inhibiting mitogen-induced cellular proliferation. SMX-HA at immunosuppressive concentrations also failed to interfere with interleukin-2 mRNA transcription and interleukin-2 protein production, which suggests that signaling events proximal to cytokine production are not affected by the metabolite. Synergy between SMX-HA/FK506 and SMX-HA/CsA suggests that the mechanism(s) of action of reactive sulfonamide metabolites may occur in later stages of lymphocyte activation.

Actins↗

PubMed1963