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At least 829 records · Page 46Linked to original sources
PubMed1997

Molecular analysis of carotenoid cyclase inhibition.

Later steps of carotenoid biosynthesis catalyzed by cyclase enzymes involve the formation of alpha, beta, and kappa-rings. Examination of the primary structure of lycopene beta-cyclase revealed 55% identity with that of antheraxanthin kappa-cyclase. Recombinant lycopene beta-cyclase afforded only beta-carotene, while recombinant antheraxanthin kappa-cyclase catalyzed the formation of beta-carotene from lycopene as well as the conversion of antheraxanthin into the kappa-carotenoid capsanthin. Since the formation of beta- and kappa-rings involves a transient carotenoid carbocation, this suggests that both cyclases initiate and/or neutralize the incipient carbocation by similar mechanisms. Several amine derivatives protonated at physiological pH were used to examine the molecular basis of this phenomenon. The beta-and kappa-cyclases displayed similar inhibition patterns. Affinity or photoaffinity labeling using p-dimethylamino-benzenediazonium fluoroborate, N,N-dimethyl-2-phenylaziridinium, and nicotine irreversibly inactivated both cyclase enzymes. Photoaffinity labeling using [3H]nicotine followed by radiosequence analysis and site-directed mutagenesis revealed the existence of two cyclase domains characterized by the presence of reactive aromatic and carboxylic amino acid residues. We propose that these residues represent the "negative point charges" involved in the coordination of the incipient carotenoid carbocations.

Affinity Labels↗
PubMed1995

The use of 96-well polystyrene plates for DNA hybridization-based assays: an evaluation of different approaches to oligonucleotide immobilization.

A reliable, simple, and cost-effective method for the immobilization of relatively short (12-30 mer) oligonucleotide probes to 96-well polystyrene plates was required in our laboratory for use in DNA hybridization-based assays. We compared three different approaches to achieve this immobilization. Two of them are modifications of previously published procedures, requiring the use of modified oligonucleotides and/or modified plates. These were compared to a method developed in our laboratory, whereby passive immobilization occurs by incubation in the presence of salt or a cationic detergent. While all methods resulted in the productive binding of the DNA probes and could therefore be used for hybridization, only the passive immobilization approach met our strict performance criteria and was implemented for use in our DNA genotyping laboratory. It was found that the immobilization in the presence of cationic detergents takes place via a unique mechanism.

Base Sequence↗
PubMed1998

Two mechanisms for toxic effects of hydroxylamines in human erythrocytes: involvement of free radicals and risk of potentiation.

The toxic potency of three industrially used hydroxylamines was studied in human blood cells in vitro. The parent compound hydroxylamine and the O-ethyl derivative gave very similar results. Both compounds induced a high degree of methemoglobin formation and glutathione depletion. Cytotoxicity was visible as Heinz body formation and hemolysis. High levels of lipid peroxidation occurred, in this respect O-ethyl hydroxylamine was more active than hydroxylamine. In contrast H2O2 induced lipid peroxidation was lowered after O-ethyl hydroxylamine or hydroxylamine treatment, this is explained by the ferrohemoglobin dependence of H2O2 induced radical species formation. Glutathione S-transferase (GST) and NADPH methemoglobin reductase (NADPH-HbR) activities were also impaired, probably as a result of the radical stress occurring. The riboflavin availability was decreased. Other enzyme activities glutathione reductase (GR), glucose 6-phosphate dehydrogenase (G6PDH), glucose phosphate isomerase and NADH methemoglobin reductase, were not or only slightly impaired by hydroxylamine or O-ethyl hydroxylamine treatment. A different scheme of reactivity was found for N,O-dimethyl hydroxylamine. This compound gave much less methemoglobin formation and no hemolysis or Heinz body formation at concentrations up to and including 7 mM. Lipid peroxidase induction was not detectable, but could be induced by subsequent H2O2 treatment. GST and NADPH-HbR activities and riboflavin availability were not decreased. On the other hand GR and G6PDH activities were inhibited. These results combined with literature data indicate the existence of two different routes of hematotoxicity induced by hydroxylamines. Hydroxylamine as well as O-alkylated derivatives primarily induce methemoglobin, a process involving radical formation. The radical stress occurring is probably responsible for most other effects. N-alkylated species like N,O-dimethyl hydroxylamine primarily lead to inhibition of the protective enzymes G6PDH and GR. Since these enzymes play a key role in the protection of erythrocytes against oxidative stress a risk of potentiation during mixed exposure does exist.

Dimethylamines↗
PubMed1990

Determination of muscarinic agonist potencies at M1 and M2 muscarinic receptors in a modified pithed rat preparation.

The agonistic potencies of (+/-)muscarine, (+/-)cis-2-methyl-5- [(dimethylamino)methyl]-1,3-oxathiolane methiodide (cis-oxathiolane) and its two enantiomers were determined at muscarinic M1 and M2 receptors in the pithed rat. In non-pretreated animals, i.v. administration of these agents produced bradycardic effects mediated by cardiac M2 receptors followed by increases in heart rate mediated by M1 receptors in sympathetic ganglia. As these responses have been shown to partly overlap, "true" M1 and M2 potencies were determined after selective blockade of M1 and M2 receptors by pirenzepine and methoctramine, respectively. A similar rank order of agonist potencies was obtained at M1 and M2 receptors: (+)cis-oxathiolane greater than (+/-)cis-oxathiolane greater than (+/-)muscarine greater than (-)cis-oxathiolane. At both receptor subtypes, (+)cis-oxathiolane was considerably more potent (ca. 30-fold) than its corresponding (-) enantiomer indicating that the agonist binding sites of the two receptor subtypes may have similar stereochemical properties. While (+/-)muscarine showed similar potencies at M1 and M2 receptors, racemic cis-oxathiolane and its two enantiomers showed a slight selectivity (3-7 fold) for M1 receptors indicating the potential usefulness of these compounds in the development of selective M1 receptor agonists.

Animals↗
PubMed1986

Determination of DNA single strand breaks and selective DNA amplification by N-nitrodimethylamine and analogs, and estimation of the indicator cells' metabolic capacities.

N-nitrodimethylamine is metabolized oxidatively to N-nitrohydroxymethylmethylamine, which decomposes to yield formaldehyde and N-nitromethylamine. All four compounds and N-nitromethylamine were tested for their ability to induce DNA single strand breaks in hepatocytes and in SV 40-transformed Chinese hamster embryo cell lines. Only the two monoalkylnitramines were positive. They induced single strand breaks in hepatocytes, but were not effective in the other cells. Formaldehyde and N-nitrohydroxymethylmethylamine were toxic to the cells. None of the compounds tested was able to induce selective DNA amplification in the two transformed cell lines. Enzymes involved in drug metabolism were assayed in the hamster cell lines. The activity of UDP-glucuronosyltransferase and cytosolic epoxide hydrolase were not detectable. N-nitrodimethylamine demethylation was low. The content of reduced glutathione and the activities of glutathione transferase and membrane bound epoxide hydrolase were comparable to values obtained in the rat liver.

Animals↗
PubMed1975

Photochemical reaction centers from Rhodopseudomonas capsulata.

A photochemically active bacteriochlorophyll-protein complex (reaction center) has been isolated from the carotenoidless mutant A1a+ of Rhodopseudomonas capsulata by treatment of membranes with lauryl dimethyl amine oxide. Three proteins with molecular weights of 20,500, 24,000 and 28,000 (molar ratio 1:1:1) were detected in the reaction center preparations. After mild treatment of intracytoplasmic membranes with Na-dodecyl sulfate (0.5%, 30 degrees C, 1 min) succeeded by polyacrylamide gel electrophoresis two pigmented bands were obtained. Material of one fraction could be bleached reversibly by actinic light and contained two proteins with molecular weights of 20,500 and 24000. The second band is photochemically inactive.

Bacterial Proteins↗
PubMed1975

Reactions of 4-halogeno-N,N-dimethylaniline-N-oxide with hemoglobin.

Incubation with ferrihemoglobin or ferricytochrome c transforms 4-bromo-N,N-dimethylaniline-N-oxide (BrDANO) into 4-bromo-N,N-dimethylaniline, 4-bromo-N-methylaniline, and 2-dimethylamino-5-bromo-phenol. In a secondary reaction 4-bromo-N'-(4-bromophenyl)-6-hydroxy-N,N,N-trimethyl-1,3-phenylenediamine (U) was found from 2-dimethylamino-5-bromo-phenol and 4-bromo-N-methylaniline. The products were isolated and identified, the structure of (U) was elucidated. It has been found that the formation of ferrihemoglobin by BrDANO is an autocatalytic reaction, ferrihemoglobin being the catalyst. BrDANO reacts with the catalyst resulting in the named products. 2-Dimetnylamino-5-bromo-phenol oxidizes hemoglobin in the presence of oxygen. Thereby the catalyst ferrihemoglobin increases, which in turn increases the transformation of BrDANO to ferrihemoglobin forming derivates. This cycyle explains the autocatalytic character of the production of ferrihemoglobulin by BrDANO. The primary products of the reaction between 4-fluoro-N,N-dimethylaniline-N-oxide (FDANO) or 4-chloro-N,N-dimethylaniline-N-oxide (ClDANO) with cytochrome c, 4-fluoro- and 4-chloro-N,N-dimethylaniline, 4-fluoro- and 4-chloro-N-methylaniline, 2-dimethylamino-5-fluoro-phenol, and 2-dimethylamino-5-chloro-phenol were isolated and identified. The reactions between N,N-dimethylaniline-N-oxide (DANO), BrDANO, ClDANO, FDANO, and hemoglobin from blood of various species were studied. BrDano and ClDANO accelerate the formation of ferrihemoglobin in solutions of hemoglobin from beef and dog blood much more effectively than DANO and FDANO.

Aniline Compounds↗