Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Dimethylamines”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 613 records · Page 34Linked to original sources
PubMed1967

Submicrodeterminations of thiols, disulphides and thiol esters in serum by using o-hydroxymercuribenzoic acid and dithiofluorescein.

1. Methods are described for selective estimation of thiols, disulphides and thiol esters in standard solutions and in serum. The methods are based on the reaction with the excess of o-hydroxymercuribenzoic acid (HMB) in alkaline solution with subsequent addition of dithiofluorescein in excess and determination of the extinction at 588mmu. The sensitivity of the methods amounts to 1.5x10(-9)g.equiv. in 5ml. of final solution. Of results obtained on standard solutions 80% have the errors within the range +/-4%. 2. It has been found that serum contains an unidentified substance (substance X) producing green complexes with dithiofluorescein which undergo decomposition on addition of formaldehyde. The correction for substance X must be estimated in a separate sample and taken into account. The concentration of substance X can be calculated from extinctions measured at 588mmu and 635mmu in the presence of dithiofluorescein in excess. 3. The selective determination of thiols and disulphides is based on different reaction rates with formaldehyde. The complexes between HMB and cysteine can be selectively decomposed by formaldehyde, and free glutathione can be selectively removed by formaldehyde in the presence of protein thiols. 4. Thiols are determined in the presence of triethylamine, thiols plus disulphides in the presence of triethylamine and sulphite, and thiols plus thiol esters in the presence of dimethylamine, with subsequent addition of ammonium sulphate.

Cysteine↗
PubMed1974

Purification and properties of the trimethylamine dehydrogenase of bacterium 4B6.

1. The trimethylamine dehydrogenase of bacterium 4B6 was purified to homogeneity as judged by analytical polyacrylamide-gel electrophoresis. The specific activity of the purified enzyme is 30-fold higher than that of crude sonic extracts. 2. The molecular weight of the enzyme is 161000. 3. The kinetic properties of the purified enzyme were studied by using an anaerobic spectrophotometric assay method allowing the determination of trimethylamine dehydrogenase activity at pH8.5, the optimum pH. The apparent K(m) for trimethylamine is 2.0+/-0.3mum and the apparent K(m) for the primary hydrogen acceptor, phenazine methosulphate, is 1.25mm. 4. Of 13 hydrogen acceptors tested, only Brilliant Cresyl Blue and Methylene Blue replace phenazine methosulphate. 5. A number of secondary and tertiary amines with N-methyl and/or N-ethyl groups are oxidized by the purified enzyme; primary amines and quaternary ammonium salts are not oxidized. Of the compounds that are oxidized by the purified enzyme, only trimethylamine and ethyldimethylamine support the growth of bacterium 4B6. 6. Trimethylamine dehydrogenase catalyses the anaerobic oxidative N-demethylation of trimethylamine with the formation of stoicheiometric amounts of dimethylamine and formaldehyde. Ethyldimethylamine is also oxidatively N-demethylated yielding ethylmethylamine and formaldehyde; diethylamine is oxidatively N-de-ethylated. 7. The activity of the purified enzyme is unaffected by chelating agents and carbonyl reagents, but is inhibited by some thiol-binding reagents and by Cu(2+), Co(2+), Ni(2+), Ag(+) and Hg(2+). Trimethylamine dehydrogenase activity is potently inhibited by trimethylsulphonium chloride, by tetramethylammonium chloride and other quaternary ammonium salts, and by monoamine oxidase inhibitors of the substituted hydrazine and the non-hydrazine types. 8. Inhibition by the substituted hydrazines is time-dependent, is prevented by the presence of trimethylamine or trimethylamine analogues and in some cases requires the presence of the hydrogen acceptor phenazine methosulphate. The inhibition was irreversible with the four substituted hydrazines that were tested.

Anaerobiosis↗
PubMed1976

A steady-state kinetic study of the reaction catalysed by the secondary-amine mono-oxygenase of Pseudomonas aminovorans.

1. Secondary-amine mono-oxygenase (proposed EC group 1.14.99.-) was partially purified from trimethylamine-grown Pseudomonas aminovorans by (NH4)2SO4 fractionation, gel filtration, hydrophobic chromatography on 5-aminopentylamino-Sepharose, and affinity chromatography on Sepharose-bound NADH. 2. Some problems in the affinity-chromatography step are discussed. 3. A steady-state kinetic analysis varying substrate, oxygen and electron-donor concentrations was performed, which, over the concentration range studied, gave a series of families of approximately parallel double-reciprocal plots. From secondary and tertiary plots, Michaelis constants of 0.160 mM, 0.086 mM and 0.121 mM were obtained for dimethylamine, NADPH and oxygen respectively. 4. Product-inhibition studies supported the postulated Hexa Uni Ping Pong (triple-transfer) reaction mechanism.

Chromatography, Affinity↗
PubMed1982

Mechanistic studies on the dehydrogenases of methylotrophic bacteria. 1. The influence of substrate binding to reduced trimethylamine dehydrogenase on the intramolecular electron transfer between its prosthetic groups.

The trimethylamine dehydrogenase of bacterium W3A1 is reduced with the formation of a triplet state in which two electrons, derived from the substrate, are distributed between the [4Fe-4S] cluster and 6-S-cysteinyl-FMN semiquinone. In titration experiments at pH 8.5 about 1.0 mol of dimethylamine or 0.5 mol of trimethylamine per mol of the enzyme is required to titrate the enzyme to an endpoint. At pH values less than 8.0, however, an excess of trimethylamine is required to obtain maximal yield of the g = 4 e.p.r. signal, characteristic of the triplet state, or maximal absorbance at 365 nm which indicates formation of the flavin semiquinone. The binding of 0.86 mol of trimethylamine per mol of the enzyme could be detected by a gel chromatographic method. When the enzyme is titrated with dithionite in the presence of tetramethylammonium chloride, an endpoint is reached after the uptake of two electrons which give rise to the triplet state, whereas three electrons are consumed in the absence of tetramethylammonium chloride to reduce the enzyme completely. The enzyme is inhibited noncompetitively by tetramethylammonium chloride and the slopes of double reciprocal plots are a concave upwards function of inhibitor concentration. The data indicate the presence of a binding site for the substrate and other amines on the reduced enzyme which enhances the proportion of enzyme in the triplet state.

Bacteria↗
PubMed1978

Hepatic metabolism of aminopyrine in patients with chronic renal failure.

1. To evaluate potential alterations in hepatic metabolism of drugs occurring in patients with renal insufficiency the fate of aminopyrine was studied in 17 patients with chronic renal failure and in 27 normal subjects. 2. Although patients with chronic renal failure exhibited large variations, their aminopyrine plasma disappearance times (mean 0.62 +/- SD 0.24 h-1) were significantly higher than those found in normal subjects (0.30 +/- 0.07 h-1, P less than 0.002). 3. 14CO2 derived from [dimethylamine-14C]aminopyrine disappeared from breath more rapidly in patients with chronic renal failure and a history of analgesic abuse (0.40 +/- 0.04 h-1) than in control subjects (0.22 +/- 0.03 h-1, P less than 0.01) and in other patients with chronic renal failure (0.24 +/- 0.04 h-1). 4. Dialysis treatment and serum creatinine concentrations were not correlated with the rates of aminopyrine metabolism. Two additional patients, however, with combined renal and hepatic disease, exhibited markedly slowed rates of aminopyrine demethylation. 5. Although chronic renal failure by itself might not alter microsomal drug metabolism it is concluded that, in patients with a history of abuse of phenacetin-containing analgesics, marked acceleration in aminopyrine N-demethylation may be observed.

Adult↗
PubMed2000

Biodegradation of didecyldimethylammonium chloride by Pseudomonas fluorescens TN4 isolated from activated sludge.

Bacteria that degrade didecyldimethylammonium chloride (DDAC) were isolated from activated sludge from a municipal sewage treatment plant by enrichment culture with DDAC as a sole carbon source. One of the isolates, Pseudomonas fluorescens TN4, degraded DDAC to produce decyldimethylamine and subsequently, dimethylamine, as the intermediates. The TN4 strain also assimilated the other quaternary ammonium compounds (QACs), alkyltrimethyl- and alkylbenzyldimethyl-ammonium salts, but not alkylpyridinium salts. TN4 was highly resistant to these QACs and degraded them by an N-dealkylation process. These data mean that there are some QAC-resistant and QAC-degrading bacteria such as TN4 in the environment.

Biodegradation, Environmental↗
PubMed1998

Phosphorylation of ethanolamine, methylethanolamine, and dimethylethanolamine by overexpressed ethanolamine kinase in NIH 3T3 cells decreases the co-mitogenic effects of ethanolamines and promotes cell survival.

Ethanolamine (Etn), as well as its N-methyl (MeEtn) and N,N-dimethyl (Me2Etn) analogues, were recently shown to potentiate the stimulatory effect of insulin on DNA synthesis in serum-starved NIH 3T3 fibroblasts. In the present work we assessed the impact of the co-mitogenic effects of Etn and its methyl analogues on cell proliferation and cell survival, and examined whether the cell growth regulatory effects of these ethanolamines involve an Etn-kinase-mediated phosphorylation step. For this purpose, NIH 3T3 sublines highly overexpressing Drosophila Etn kinase and an appropriate vector control line were utilized and the effects of Etn, MeEtn, Me2Etn, methylamine (MeNH2), and dimethylamine (Me2NH) were studied. 31P-NMR analysis of the water-soluble cell metabolites revealed that both MeEtn and Me2Etn, but not choline, are excellent substrates for the expressed Etn kinase. The methylated ethanolamines (MeEtn and Me2Etn) and methylamines (MeNH2, Me2NH) were used as Etn models that can or cannot be phosphorylated, respectively. In serum-starved vector control cells, both MeNH2 (1 mM) and Me2NH (1 mM) were more effective than Etn in enhancing insulin-induced DNA synthesis, and both were almost as effective as MeEtn and Me2Etn. However, in the Etn kinase overexpressor cells the potentiating effects of Etn, MeEtn and Me2Etn, but not those of MeNH2 and Me2NH, were significantly reduced. Moreover, in the overexpressor cells, lower concentrations of Etn (50-200 microM) inhibited the combined mitogenic effects of Me2NH (1 mM) and insulin. These data are consistent with a mechanism in which the phosphorylated and non-phosphorylated ethanolamines are negative and positive regulators of insulin-induced mitogenesis, respectively. After incubating the cells for 13 days in serum-free medium in 96-well microplates, there was a steady decrease in cell numbers in both cell lines. However, between 6-13 days, 0.1-1 mM MeEtn and, particularly, Me2Etn provided significant protection against cell death in the Etn kinase overexpressor cells. In vector control cells, only Me2Etn in combination with insulin had similar effects on cell survival. The data suggest that phosphorylated ethanolamines may function as promoters of cell survival.

3T3 Cells↗
PubMed2001

Relationship of asymmetric dimethylarginine to dialysis treatment and atherosclerotic disease.

Asymmetric dimethylarginine (ADMA) is an endogenous inhibitor of endothelial nitric oxide (NO) synthase. Its concentration is elevated in patients with end-stage renal disease (ESRD), in part because it is excreted via the kidneys. In addition, ADMA is degraded by the enzyme dimethylarginine dimethylaminohydrolase (DDAH), which hydrolyzes ADMA to L-citrulline and dimethylamine. Activity of DDAH is decreased by oxidized low density lipoprotein (LDL) or tumor necrosis factor-alpha (TNF-alpha) in vitro yielding increased levels of ADMA. Furthermore, plasma levels of ADMA are elevated in hyperhomocyst(e)inemia and in hypertensive patients on a high salt diet. Data from several experimental studies suggest that ADMA concentrations in a pathophysiologically high range (3 to 10 micromol/L) significantly inhibit vascular NO formation by NO synthase in the presence of L-arginine in isolated human blood vessels, cultured macrophages, and in cultured endothelial cells. It has been well demonstrated that ADMA accumulates in chronic renal failure. Although there is controversy concerning the absolute concentration of ADMA, all authors found a two- to sixfold increase in ADMA levels in patients in chronic renal failure as compared to controls. Different dialysis treatment strategies differentially affect ADMA levels. The presence of atherosclerosis is associated with higher ADMA levels in patients with normal renal function as well as in dialysis patients, but this phenomenon may be unrelated to renal handling of ADMA. Reduced NO elaboration secondary to accumulation of ADMA may be an important pathogenic factor for atherosclerosis in chronic renal failure and ADMA may be a new uremic toxin. Clinical studies on the effect of ADMA are needed to further elucidate its pathophysiological role in atherosclerosis and uremia.

Arginine↗
PubMed2000

Development of a DNA immunoadsorbent: coupling DNA on sepharose 4FF by an efficient activation method.

To remove anti-DNA antibodies from a patient's plasma with systemic lupus erythematosus (SLE), a DNA immunoadsorbent was developed by covalently coupling calf thymus DNA on activated Sepharose 4FF. Sepharose 4FF was activated with 5-norbornene-2,3-dicarboximido carbonochloridate (Cl-CO-ONB), which was proven to be a very effective method for preparation of affinity chromatographic adsorbents. The activation was carried out in dry acetone using 4-(dimethylamine)pyridine (DMAP) and triethylamine (TEA) as catalysts at 4 degrees C or at room temperature. The coupling of DNA to the activated support was investigated as a function of pH, temperature, time, concentration of DNA, and activation level. It was found that the pH for optimal coupling is 3.0, and the amount of coupled DNA increases with an increase either in the concentration of DNA or the activation level. The maximum amount of coupled DNA could reach 1.0 mg DNA/ml support. The incubation of 5 to 20 ml of SLE plasma with 1.0 ml of adsorbent resulted in an 80 to 90% decline in the anti-DNA antibody level. Nonspecific adsorption for normal IgG and total protein is less than 15%.

Acetone↗
PubMed2004

Synthesis of some mono-Mannich bases and corresponding azine derivatives and evaluation of their anticonvulsant activity.

Mono-Mannich bases, 3-amino-1-aryl-1-propanone hydrochlorides (Ig1-Ig4), and their corresponding azine derivatives, N,N'-bis(3- amino-1-aryl-propylidene) hydrazine dihydrochlorides (D1-D4), were synthesized and their anticonvulsant activities were evaluated. Alterations in biological activity depending on modifications in chemical structure were also followed. The aryl part was phenyl in Ig1, D1, Ig2, D2, Ig3, D3, or p-hydroxyphenyl in Ig4, and D4. The amine part was dimethylamine in Ig1, D1, Ig4, and D4, piperidine in Ig2, D2 or morpholine in Ig3, D3. Compounds D2, D3, and D4 are new. The anticonvulsant activity was determined by maximal electroshock (MES) and subcutaneous metrazole (pentetrazol; scMet) tests. The rotorod toxicity test was used for determining neurological deficits. While the compounds were not effective in scMet, they were found to exert protective effect in MES. The results of MES are as follows: Compound [dose level (mg/kg), time (h)]: Ig1 [30 (0.5 h), 100 (0.5 h)]; Ig2 [30 (0.5 h, 4 h)]; Ig3 [30 (0.5 h), 100 (0.5 h), 300 (0.5 h, 4 h)]; Ig4 [300 (0.5 h, 4 h), 100 (4 h)]; D1 [30 (0.5 h)]; D3 [100 (0.5 h,4 h), 300 (0.5 h), 30 (4 h)]]; D4 [300 (0.5 h, 4 h)]. D2 did not show any anticonvulsant activity in both tests. Ig1, Ig2, D1, D2, and D3 exhibited neurotoxicity. Compounds Ig2, D1, and D2 were neurotoxic at 100 mg/kg dose level at 0.5 h. Ig1 was neurotoxic at 300 mg at 0.5 h, D3 was neurotoxic at 300 mg at 4 h. Conversion of mono-Mannich bases to their corresponding azine derivatives generally decreased the anticonvulsant activity. Ig3, Ig4 and D4 seem to be promising candidates to develop new anticonvulsant compounds for grand mal epilepsy for further synthesis and in vivo studies, since they were effective in MES screening and no neurotoxicity was observed with them.

Animals↗
PubMed2006

Metabolic profiling reveals a contribution of gut microbiota to fatty liver phenotype in insulin-resistant mice.

Here, we study the intricate relationship between gut microbiota and host cometabolic phenotypes associated with dietary-induced impaired glucose homeostasis and nonalcoholic fatty liver disease (NAFLD) in a mouse strain (129S6) known to be susceptible to these disease traits, using plasma and urine metabotyping, achieved by (1)H NMR spectroscopy. Multivariate statistical modeling of the spectra shows that the genetic predisposition of the 129S6 mouse to impaired glucose homeostasis and NAFLD is associated with disruptions of choline metabolism, i.e., low circulating levels of plasma phosphatidylcholine and high urinary excretion of methylamines (dimethylamine, trimethylamine, and trimethylamine-N-oxide), coprocessed by symbiotic gut microbiota and mammalian enzyme systems. Conversion of choline into methylamines by microbiota in strain 129S6 on a high-fat diet reduces the bioavailability of choline and mimics the effect of choline-deficient diets, causing NAFLD. These data also indicate that gut microbiota may play an active role in the development of insulin resistance.

Animals↗
PubMed1975

Resonance Raman spectroscopic studies of the interactions between trypsin and a competitive inhibitor.

Raman spectroscopy was used to study the interactions between bovine trypsin and a competitive inhibitor. For this purpose, a chromophoric substrate analogue, 4-amidino-4'-dimethylamine azobenzene, was synthesized. This compound competitively inhibits the enzyme with a 1:1 stoichiometry and an inhibition constant Ki of 2.3 muM at pH 6.08 and 15 degrees. Resonance Raman spectra in aqueous solution of free or enzyme-bound inhibitor were analyzed. The main spectral changes observed upon enzyme-inhibitor complex formation were changes in the relative intensities of four bands (1171, 1206, 1315, 1608 cm-1) while no large frequency shifts occurred. The binding of the inhibitor molecule to the enzyme did not induce a twisting of the phenyl groups around the N=N bond. Some modifications of the band widths are interpreted in terms of a restriction of rotational motions in the inhibitor molecule. The possible involvement of specific interactions between trypsin and the benzamidinium ion part of the inhibitor molecule is discussed.

Azo Compounds↗
PubMed1979

Cellular energy metabolism, trans-plasma and trans-mitochondrial membrane potentials, and pH gradients in mouse neuroblastoma.

A method for quantitative evaluation of transmembrane electrical potential and pH gradients across a subcellular compartment in an intact cell is presented. This approach has been applied in studies of mouse neuroblastoma C-1300 clone NB41A3, in which the transmembrane electrical potential and pH gradients and the mitochondrial volume percent have been determined. Membrane potentials and pH gradients were measured by two different methods. Equilibrium distributions of [(3)H]triphenylmethyl phosphonium and [(14)C]-thiocyanate ions gave calculated apparent membrane potentials of -77.0 and -29.6 mV, respectively, at 20-25 degrees C; a value of -60.8 mV was obtained from microelectrode measurements. Equilibrium distributions of weak acids ([(14)C]trimethylacetic acid and 5,5-di[(14)C]methyl-2,4-oxazolidine-dione) and of weak bases ([(14)C]dimethylamine and [(14)C]trimethylamine) gave calculated upper and lower limits of the pH gradient (Delta pH = pH(e) - pH(i)) of -0.14 and -0.21 pH unit, respectively. The microelectrode measurements showed that the intracellular pH is within 0.1 of a pH unit or less of the extracellular pH over the extracellular pH range of 7.35-6.85. The mitochondrial volume percent calculated on the basis of the measured cytochrome c content is 5.6 +/- 1.2% and compares well with estimates of 5.4 +/- 1.1% obtained from 25 electron micrographs. Measurements of the cellular energetic parameters gave values within the range found in other cells and perfused organs. Comparison of the results of the microelectrode and equilibrium measurements permits estimates of the electrical potential and pH gradients across the mitochondrial membrane (mitochondria-to-cytoplasm gradients) to be made and suggests that the trans-mitochondrial membrane protonmotive force in the intact cell cannot be greater than -143 mV.

Animals↗
PubMed1981

B850 pigment-protein complex of Rhodopseudomonas sphaeroides: Extinction coefficients, circular dichroism, and the reversible binding of bacteriochlorophyll.

Chromatophores of Rhodopseudomonas sphaeroides yield the antenna complex B850 in either of two states, depending on the method of isolation. Methods using dodecyl (= lauryl) dimethylamine oxide yield B850 with an absorption spectrum like that in vivo: the bands at 800 and 850 nm, due to the bacteriochlorophyll (Bchl) components Bchl-800 and Bchl-850, are in ratio A(800)/A(850) = 0.65 +/- 0.05. When B850 is isolated by methods using dodecyl sulfate, the Bchl-800 is attenuated or absent. Bchl assays of these materials and of the isolated antenna complex B875 yielded the following extinction coefficients, +/-SD, on the basis of the molarity of Bchl: For B875, epsilon(875) = 126 +/- 8 mM(-1) cm(-1). For B850 in the normal (high-Bchl-800) state, epsilon(850) = 132 +/- 10 mM(-1) cm(-1). For the individual components of Bchl in B850, epsilon(850) of Bchl-850 = 184 +/- 13 mM(-1) cm(-1) and epsilon(800) of Bchl-800 = 213 +/- 28 mM(-1) cm(-1). With these coefficients the molecular ratio of Bchl-850 to Bchl-800 equals 1.8 +/- 0.4 for B850 in the high-Bchl-800 state. Starting with B850 depleted of Bchl-800, the addition of dodecyldimethylamine oxide restored the 800-nm absorption band. The 850-nm band became shifted toward the blue, narrowed, and slightly attenuated, and its associated circular dichroism became 20% more intense. Free Bchl added with dodecyldimethylamine oxide accelerated the restoration of Bchl-800 and retarded the attenuation of Bchl-850. We conclude that free Bchl can interact reversibly with a binding site for Bchl-800 in the B850 complex, with dodecyl sulfate favoring dissociation and dodecyldimethylamine oxide promoting association. Thus the reversible dissociation of a native chlorophyll-protein complex has now been demonstrated.

Journal Article↗
PubMed1997

Reconstitution of Monomethylamine:Coenzyme M methyl transfer with a corrinoid protein and two methyltransferases purified from Methanosarcina barkeri.

Methanogenesis from methylamines requires the intermediate methylation of 2-mercaptoethanesulfonate (CoM). In vitro reconstitution of CoM methylation with monomethylamine was achieved with three purified proteins: a monomethylamine corrinoid protein (MMCP), the "A" isozyme of methylcobamide:CoM methyltransferase (MT2-A), and a newly isolated protein termed monomethylamine methyltransferase (MMAMT).MMAMT is a 170-kDa protein with 52-kDa subunits. The MMAMT polypeptide was rate-limiting for methyl transfer until at a 2-fold molar excess over MMCP. MMAMT is a monomethylamine:MMCP methyltransferase, since methylation of MMCP required MMAMT but not MT2-A. MMCP and MMAMT formed a complex detectable by size exclusion high pressure liquid chromatography. Methyl group transfer from methyl-MMCP to CoM was mediated by MT2-A, since methyl iodide:CoM methyl transfer by MMCP and MT2-A did not require MMAMT. MT2-M, an isozyme of MT2-A, was inactive in MMCP-dependent methyl transfer. Immunodepletion of MMCP from the extract inhibited CoM methylation with monomethylamine but not dimethylamine. Purified MMCP reconstituted activity in immunodepleted extracts. These results show that MMCP is the major corrinoid protein for methanogenesis from monomethylamine detectable in extracts and that it interacts with two methyltransferases. MMAMT functions as a MMA:MMCP methyltransferase, while MT2-A functions as a methyl-MMCP:CoM methyltransferase.

Bacterial Proteins↗
PubMed1997

Photoinactivation of the F1-ATPase from spinach chloroplasts by dequalinium is accompanied by derivatization of methionine beta183.

In contrast to the F1-ATPases from bovine mitochondria and the thermophilic Bacillus PS3, which are reversibly inhibited by dequalinium in the absence of irradiation, the Mg2+-ATPase activity of heat- or dithiothreitol-activated chloroplast F1 (CF1) from spinach chloroplasts is slightly stimulated by dequalinium. Conversely, dequalinium is a partial inhibitor (maximal inhibition is 85-90%) of the Ca2+-ATPase of CF1 activated by heat, dithiothreitol, or octylglucoside. The Mg2+- and Ca2+-ATPase activities of CF1 respond differently in the presence of lauryl dimethylamine oxide (LDAO) in the assay medium. Whereas the Mg2+-ATPase activity of heat- or dithiothreitol-activated CF1 is stimulated up to 14-fold by increasing concentrations of LDAO, the Ca2+-ATPase is inhibited in a biphasic manner by increasing concentrations of LDAO. In the presence of LDAO, dequalinium does not stimulate the heat-activated Mg2+-ATPase over that promoted by LDAO alone. That dequalinium slightly stimulates Mg2+-ATPase activity although it inhibits Ca2+-ATPase activity can be reconciled by assuming that dequalinium binds to two sites in CF1, a stimulatory site that also binds LDAO and an inhibitory site. By acting as a partial inhibitor of the Mg2+-ATPase activity that it activates, the combined effect of dequalinium is modest stimulation. Irradiation of heat- or dithiothreitol-activated CF1 or the alpha3beta3gamma subcomplex of CF1 in the presence of 12 microM dequalinium led to rapid photoinactivation. ATP and ADP, separately or in combination with Mg2+, protect against photoinactivation. After photoinactivating the alpha3beta3gamma subcomplex of CF1 with [14C]dequalinium, tryptic and peptic digests of the isolated, derivatized beta subunit were fractionated by high performance liquid chromatography. Sequencing of the isolated, radioactive tryptic and peptic peptides revealed that Metbeta183, which is at or near the catalytic site, is derivatized in a single beta subunit when CF1 is photoinactivated with [14C]dequalinium.

Ca(2+) Mg(2+)-ATPase↗
PubMed1998

Bacterial expression and characterization of the mitochondrial outer membrane channel. Effects of n-terminal modifications.

Several forms of the voltage-dependent anion-selective channel (VDAC) have been expressed at high yield in Escherichia coli. Full-length constructs of the proteins of Neurospora crassa and Saccharomyces cerevisiae (ncVDAC and scVDAC) have been made with 20-residue-long, thrombin-cleavable, His6-containing N-terminal extensions. ncVDAC purified from bacteria or mitochondria displays a far-UV CD spectrum (in 1% lauryl dimethylamine oxide at pH 6-8) similar to that of bacterial porins, indicating extensive beta-sheet structure. Under the same conditions, the CD spectrum of bacterially expressed scVDAC indicates lower beta-sheet content, albeit higher than that of mitochondrial scVDAC under the same conditions. In phospholipid bilayers, the bacterially expressed proteins (with or without N-terminal extensions) form typical VDAC-like channels with stable, large conductance open states (4-4.5 nanosiemens in 1 M KCl) and voltage-dependent transitions to a predominant substate (about 2 nanosiemens). A variant of scVDAC missing the first eight residues and having no N-terminal extension also has been expressed in E. coli. The truncated protein has a CD spectrum similar to that of mitochondrial scVDAC, but its channel activity is abnormal, exhibiting an unstable open state and rapid transitions between multiple subconductance levels.

Amino Acid Sequence↗
PubMed1999

The reaction of trimethylamine dehydrogenase with trimethylamine.

The reductive half-reaction of trimethylamine dehydrogenase with its physiological substrate trimethylamine has been examined by stopped-flow spectroscopy over the pH range 6.0-11.0, with attention focusing on the fastest of the three kinetic phases of the reaction, the flavin reduction/substrate oxidation process. As in previous work with the slow substrate diethylmethylamine, the reaction is found to consist of three well resolved kinetic phases. The observed rate constant for the fast phase exhibits hyperbolic dependence on the substrate concentration with an extrapolated limiting rate constant (klim) greater than 1000 s-1 at pH above 8.5, 10 degrees C. The kinetic parameter klim/Kd for the fast phase exhibits a bell-shaped pH dependence, with two pKa values of 9.3 +/- 0.1 and 10. 0 +/- 0.1 attributed to a basic residue in the enzyme active site and the ionization of the free substrate, respectively. The sigmoidal pH profile for klim gives a single pKa value of 7.1 +/- 0. 2. The observed rate constants for both the intermediate and slow phases are found to decrease as the substrate concentration is increased. The steady-state kinetic behavior of trimethylamine dehydrogenase with trimethylamine has also been examined, and is found to be adequately described without invoking a second, inhibitory substrate-binding site. The present results demonstrate that: (a) substrate must be protonated in order to bind to the enzyme; (b) an ionization group on the enzyme is involved in substrate binding; (c) an active site general base is involved, but not strictly required, in the oxidation of substrate; (d) the fast phase of the reaction with native enzyme is considerably faster than observed with enzyme isolated from Methylophilus methylotrophus that has been grown up on dimethylamine; and (e) a discrete inhibitory substrate-binding site is not required to account for excess substrate inhibition, the kinetic behavior of trimethylamine dehydrogenase can be readily explained in the context of the known properties of the enzyme.

Catalysis↗