SEARCH · Search PubMed

Results for “ALKYLATION”

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.

SourceResearch connectionFrom yearThrough year

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

At least 703 records · Page 39Linked to original sources

PubMed1999

The Effect of Anomeric Head Groups, Surfactant Hydrophilicity, and Electrolytes on n-Alkyl Monoglucoside Microemulsions.

The effects of the variables of head group structure and salt concentration on microemulsions formed in mixtures of water, alkyl ethylene glycol ethers (CkOC2OCk), and n-alkyl beta-d-glucopyranosides (CmbetaG1) are explored. Phase behavior of mixtures containing an anomer of the surfactant (n-alkyl alpha-d-glucopyranoside, CmalphaG1), or surfactants with long head groups (n-alkyl maltopyranosides, CmG2), or NaCl or NaClO4 as electrolyte are systematically reported as a function of temperature and composition. The substitution of n-alkyl alpha-d-glucopyranosides for n-alkyl beta-d-glucopyranosides causes precipitation under some conditions in all mixtures studied. These solubility boundaries begin in the water-surfactant binary mixture at the Krafft boundary, then extend to high concentrations of both surfactant and oil. Increasing the effective length of the surfactant head group by adding CmG2 to water-CkOC2OCk-CmbetaG1 mixtures moves the phase behavior dramatically up in temperature when even small amounts of CmG2 are used. Adding a lyotropic electrolyte, NaCl, to water-CkOC2OCk-CmbetaG1 mixtures moves the phase behavior down in temperature, while the hydrotropic electrolyte NaClO4 moves the phase behavior up in temperature. Copyright 1999 Academic Press.

Journal Article↗

PubMed1983

1-O-alkyl-linked phosphoglycerides of human platelets: distribution of arachidonate and other acyl residues in the ether-linked and diacyl species.

In this study, the 1-O-alkyl-2-acyl-sn-glycero-3-phosphocholine content of human platelets was determined. The distribution of arachidonate among the 1,2-diacyl, 1-O-alkyl-2-acyl, and 1-O-alk-l'-enyl-2-acyl classes of choline- and ethanolamine-containing phosphoglycerides was also assessed. The major platelet phospholipids were choline-containing phosphoglycerides (38%), ethanolamine-containing phosphoglycerides (25%) and sphingomyelin (18%), with smaller amounts of phosphatidylserine (11%) and phosphatidylinositol (4%). In addition to the diacyl class, the choline-linked fraction was found to contain both 1-O-alkyl-2-acyl (10%) and 1-O-alk-l'-enyl-2-acyl (9%) species. The ethanolamine-linked fraction, on the other hand, had an elevated level of the 1-O-alk-1'-enyl-2-acyl (60%) species and a small amount of the 1-O-alkyl-2-acyl component (4%). The major fatty acyl residues found in all classes of the choline and ethanolamine phospholipids were 16:0, 18:0, 18:1 (delta 9), 18:2(n-6) and 20:4(n-6). The 1-O-alkyl and 1-O-alk-1'-enyl fraction of the ethanolamine-linked phospholipids also contained substantial amounts of 22:5(n-3) and 22:6(n-3) acyl chains. Arachidonate comprised 44% of the acyl residues in the sn-2 position of 1-O-alkyl-2-acyl-sn-glycero-3-phosphocholine. Corresponding values for the diacyl and 1-O-alk-1'-enyl-2-acyl species were 23% and 25%, respectively, based on all 20:4(n-6) being linked to the sn-2 position of all classes.(ABSTRACT TRUNCATED AT 250 WORDS)

Arachidonic Acid↗

PubMed1986

The modes of action of long chain alkyl compounds on the respiratory chain-linked energy transducing system in submitochondrial particles.

The interactions of long chain (greater than C7), alkyl compounds with tightly coupled, beef heart submitochondrial particles (SMP) have been investigated with respect to their effects upon respiratory chain-linked electron transfer and energy coupling capacity. Long chain alkyl alcohols, amines, free fatty acids, and methyl esters exhibit a general uncoupling effect, with stimulation of the succinate oxidase activity but inhibition of the NADH oxidase, in SMP. The degree of effectiveness is dependent on the nature of the functional group and the length of the alkyl chain. Submitochondrial particles depleted of F1 and the F1-inhibitor protein are similarly affected. Subsequent treatment with bovine serum albumin reverses the effects of free fatty acids and results in partial recovery of activity with alkyl amines, alcohols, and methyl esters. Differences between the effects of these alkyl compounds and those of sodium dodecyl sulfate, deoxycholate, palmitoyl carnitine, and palmitoyl CoA rule out detergent-like action as the explanation for these observations. These data suggest that specific lipophilic interactions with the membrane, modulated by the nature of the functional group, are responsible for the effects of these compounds on the energy transducing system of SMP. Analyses of the reduction kinetics of the cytochromes indicate that the sites of interaction of these compounds with the inner mitochondrial membrane are associated with the primary dehydrogenase of complex I and energy coupling site 2; alkyl amines possess an additional site of interaction in the region of complex III.

Alcohols↗

PubMed1986

Spin-label studies on phosphatidylcholine-cholesterol membranes: effects of alkyl chain length and unsaturation in the fluid phase.

Dynamic properties of phosphatidylcholine-cholesterol membranes in the fluid phase and water accessibility to the membranes have been studied as a function of phospholipid alkyl chain length, saturation, mole fraction of cholesterol, and temperature by using spin and fluorescence labelling methods. The results are the following: (1) The effect of cholesterol on motional freedom of 5-doxyl stearic acid spin label (5-SASL) and 16-doxyl stearic acid spin label (16-SASL) in saturated phosphatidylcholine membrane is significantly larger than the effects of alkyl chain length and introduction of unsaturation in the alkyl chain. (2) Variation of alkyl chain length of saturated phospholipids does not alter the effects of cholesterol except in the case of dilauroylphosphatidylcholine, which possesses the shortest alkyl chains (12 carbons) used in this work. (3) Unsaturation of the alkyl chains greatly reduces the ordering effect of cholesterol at C-5 and C-16 positions although unsaturation alone gives only minor fluidizing effects. (4) Introduction of 30 mol% cholesterol to dimyristoylphosphatidylcholine membranes decreases the lateral diffusion constants of lipids by a factor of four, while it causes only a slight decrease of lateral diffusion in dioleoylphosphatidylcholine membranes. (5) If compared at the same temperature, 5-SASL mobilities plotted as a function of mole fraction of cholesterol in the fluid phases of dimyristoylphosphatidylcholine-, dipalmitoylphosphatidylcholine- and distearoylphosphatidylcholine-cholesterol membranes are similar in wide ranges of temperature (45-82 degrees C) and cholesterol mole fraction (0-50%). (6) In isothermal experiments with saturated phosphatidylcholine membranes, 5-SASL is maximally immobilized at the phase boundary between Regions I and III reported by other workers (Recktenwald, D.J. and McConnell, H.M. (1981) Biochemistry 20, 4505-4510) and becomes more mobile away from the boundary in Regions I and III. (7) 5-SASL in unsaturated phosphatidylcholine membranes showed a gradual monotonic immobilization with increase of cholesterol mole fraction without showing any maximum in the range of cholesterol fractions studied. (8) By rigorously determining rigid-limit magnetic parameters of cholestane spin labels in membranes from Q-band second-derivative ESR spectra to monitor the dielectric environment around the nitroxide radical, it is concluded that cholesterol incorporation increases water accessibility in the hydrophilic loci of the membrane. In contrast, 12-(9-anthroyloxy)stearic acid fluorescence showed that water accessibility is decreased in the hydrophobic loci of the membrane.

Cholesterol↗

PubMed1980

Studies on thermal adaptation in Tetrahymena membrane lipids. Positional distribution of fatty acid in diacyl- and alkyl-acyl-phosphatidylcholines and -(2-aminoethyl)phosphonolipids from cells grown at different temperatures.

Phosphatidylcholine and 2-aminoethylphosphonolipid, major membrane phospholipids in Tetrahymena, comprise 1,2-diacyl and 1-alkyl-2-acyl moieties, whereas phosphatidylethanolamine is solely in diacyl form. The overall fatty acid composition of phosphatidylcholine and 2-aminoethylphosphonolipid fractions from 15 degrees C-grown cells mainly consisted of linoleic (C18 : 2 delta 9,12) and gamma-linolenic (C18 : 3 delta 6,9,12) acids, except for the large amount of an usual fatty acid, cilienic acid (C18 : 2 delta 6,11) in 2-aminoethylphosphonolipids. When compared with 39.5 degrees C-grown cells, the 1-position of phosphatidylcholine and 2-aminoethylphosphonolipid from 15 degrees C-grown cells undergoes a large increase in palmitoleic (C16 : 1 delta 9) and gamma-linolenic acids with a corresponding decrease of myristic (C14 : 0) and palmitic (C16 : 0) acids. At the 2-position of 15 degrees C-grown cells, linoleic and gamma-linolenic acids in phosphatidylcholine, and cilienic and linoleic acids in 2-aminoethylphosphonolipid increase with a large decrease of palmitoleic acid in both phospholipids and of gamma-linolenic acid in 2-aminoethylphosphonolipid. There was quite a similarity in fatty acid composition between 1,2-diacylphosphatidylcholine and 1,2-diacyl-(2-aminoethyl)phosphonolipid in 39.5 degrees C- and 15 degrees C-grown cells. However, a marked increase of gamma-linolenic acid at the 1-position of 1,2-diacyl-phosphatidylcholine, and of linoleic acid at the 2-position of diacyl-aminoethylphosphonolipid was observed in 15 degrees C-grown cells. The 2-position of 1-alkyl-2-acyl-phosphatidylcholine and 1-alkyl-2-acyl-(2-aminoethyl)phosphonolipid was occupied mainly by unsaturated fatty acids. In 15 degrees C-grown cells, the sum of linoleic and gamma-linolenic acids accounted for 79.9% in 1-alkyl-2-acyl-phosphatidylcholine and 87.1% in 1-alkyl-2-acyl-(2-aminoethyl)phosphonolipid. These data support the hypothesis that 2-aminoethylphosphonolipid and phosphatidylcholine would play an important role as acceptors of polyunsaturated fatty acids (C18 : 2 delta 6,11, C18 : 2 delta 9,12 and C18: 3 delta 6,9,12) for temperature acclimation. Furthermore, changes in the ratio of diacyl- to alkyl-acylphosphatidylcholine may also be involved in thermal adaptation by regulating the number of fatty acid acceptor.

Animals↗

PubMed1980

A study of substrate specificity of mammalian and bacterial DNA polymerases with 5-alkyl-2'-deoxyuridine 5'-triphosphates.

DNA polymerases from procaryotic sources can utilize a variety of dTTP analogues as substrates. We studied here in vitro DNA syntheses catalyzed by DNA polymerase alpha and beta of calf thymus, and for comparison, by the Escherichia coli DNA polymerase I large fragment enzyme in the presence of 5-alkyl derivatives of dUTP as dTTP substrate analogues, using activated DNA as template-primer. The alkyl substituents were n-alkyl (from ethyl to hexyl) and iso-alkyl (isopropyl and tert-butyl) groups. All enzymes were active in the presence of each modified dTTP, incorporation rates of [3H]dAMP or [3H]dGMP were, however, much lower with the analogues than with dTTP. According to relative incorporation rates, alpha-polymerase in DNA synthesis was found to be less sensitive to changes in the length of the alkyl substituent of 5-n-alkyl-dUTPs than beta-polymerase or the E. coli enzyme. Evidence for the incorporation of the analogues was presented for 5-[2-14C]isopropyl-dUTP.

Animals↗

PubMed1984

Repair and replication of DNA in rat and mouse tissues in relation to cancer induction by N-nitroso-N-alkyl-ureas.

The high susceptibility of certain organs, for example rat brain, to induction of cancer by N-nitroso-N-alkyl-ureas, has been related to a low ability to remove O6-alkylguanine (O6AG) from DNA. It is therefore reasonable to ask why mouse brain, in which there is also a slow disappearance of O6AG from DNA after treatment with nitroso-alkyl-ureas, is not susceptible and why, in mice, thymus and lung are the main target organs. The explanation of the species difference could lie in the fact that replication of alkylated DNA is an essential event in initiation. If nitroso-alkyl-ureas had a greater inhibitory effect in some organs than in others, replication might be inhibited until after the O6AG had been removed, so preventing replication of DNA while still alkylated. This concept was tested by comparing the effect of N-nitroso-N-methyl-urea (NMU) on incorporation of [3H]TdR into DNA of relevant organs in Wistar rats and C57BL mice, and by determining ability to remove O6AG from DNA by measuring the alkyl acceptor protein (AAP) concentrations in these organs. No evidence was obtained that the AAP content was lower or inhibition of replication was less extensive in the organ of the species more susceptible to carcinogenesis than in the same organ of the less susceptible species.

Alkanes↗

PubMed1983

Cytotoxicity of monofunctional alkylating agents. Methyl methanesulfonate and methyl-N'-nitro-N-nitrosoguanidine have different mechanisms of toxicity for 10T1/2 cells.

N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) and methyl methanesulfonate (MMS) are directly active alkylating agents that methylate cellular macromolecules by SN1 and SN2 mechanisms, respectively. These two chemicals produce similar types of alkylation products in DNA and a similar level of total alkylations on a molar basis, but strikingly different proportions of alkylations of ring oxygen atoms of purines and pyrimidines. Because of this attribute, they have been used in combination to attempt to determine which types of alkylation products are responsible for mutation, transformation, and toxicity. Studies have suggested that the mutation rates produced by these and similar chemicals in cells surviving toxicity correlate well with the number of methyl adducts at the O6 position of guanine, but that cytotoxicity (reduced colony-forming efficiency) does not correlate with any single adduct or with the total level of alkylation of DNA. In this study we have investigated the cytotoxic mechanisms of MNNG and MMS in synchronized 10T1/2 cells, using colony-forming ability as a measure of toxicity. Both MNNG and MMS cause dose-dependent reduction in the ability of 10T1/2 cells to produce colonies of more than 50 cells after 2 weeks in culture. MNNG is about 100-fold more toxic than MMS on a molar basis. As indicated by the inability of cells to exclude trypan blue, MMS kills a fraction of the population of treated 10T1/2 cells after a 30-min exposure; the fraction of cells that excludes trypan blue is correlated with dose of MMS and with colony-forming efficiency. Neither the fraction of cells that is permeable to trypan blue nor the relative colony-forming efficiency is affected by the phase of the cycle when 10T1/2 cells are treated with MMS. Furthermore, MMS toxicity for 10T1/2 cells is not potentiated by caffeine, MMS treatment does not delay progress of S phase, and cells that survive acute membrane toxicity complete the cell cycle without significant delay. In contrast, MNNG treatment produces toxicity that is maximal when 10T1/2 cells are exposed during the S phase and the effect is potentiated by caffeine. MNNG treatment delays DNA replication and this delay is reversed by caffeine. In sharp contrast to 10T1/2 cells treated with MMS, MNNG-treated cells are not made permeable to trypan blue, but are blocked in their ability to proliferate. These observations indicate that MNNG and MMs kill 10T1/2 cells by drastically different mechanisms, MNNG producing toxicity mainly by preventing chromosome replication and MMS producing toxicity mainly by damaging cell membranes.

Animals↗

PubMed1987

Mutagenicity of a series of N-alkyl-, N-hydroxyalkyl-, N-haloalkyl- and N-carboxyalkyl-N-nitrosoureas in Escherichia coli tester strains: dependence on the uvrA DNA-repair system.

A series of N-alkyl-, N-hydroxyalkyl-, N-haloalkyl- and N-carboxyalkyl-N-nitrosoureas and some related derivatives were tested for mutagenicity in E. coli B (Arg-) H/r30R (wild-type) and its isogenic Hs30R (uvrA) tester strains. Mutagenic potency in Hs30R, in general, appears to depend on the substituent (-OH, -OCH3, -halogen, -COO- or -COOCH3) on the alkyl group, rather than the chain length or branching of the alkyl group. On the other hand, mutagenic potency in the wild-type H/r30R strain depends on buliness of the substituent and alkyl moiety. The term "uvrA-dependence" of mutation frequency is then defined as the ratio of the mutation frequency in Hs30R versus that in H/r30R at 1 mM dose of mutagens. Its dependence on structure is also discussed. A good correlation was found with the van der Waals volume of the substituted alkyl group, except for compounds having a carboxyalkyl or a branched alkyl group. The carboxyalkyl derivatives are the most weakly mutagenic and most seriously "uvrA-dependent", probably due to the negative charge of the molecule. The possibility of forming epoxides and lactones from N-hydroxyalkyl- and N-carboxyalkyl-N-nitrosoureas, respectively, and their participation in mutagenic potency are discussed. An attempt to correlate the partition property and activation rate of the N-nitrosoureas with mutagenic characteristics proved unsuccessful.

Bacterial Proteins↗

PubMed2005

Exploring the active site of phenylethanolamine N-methyltransferase: 3-alkyl-7-substituted-1,2,3,4-tetrahydroisoquinoline inhibitors.

A series of 3-alkyl-7-substituted-1,2,3,4-tetrahydroisoquinolines was synthesized and these compounds were evaluated for their PNMT inhibitory potency and affinity for the alpha2-adrenoceptor. 7-Nitro-, 7-bromo-, 7-aminosulfonyl-, or 7-N-2,2,2-trifluoroethylaminosulfonyl-THIQs that possess a 3-alkyl substituent that is longer than a methyl group showed decreased PNMT inhibitory potency, except for 3-propyl-7-aminosulfonyl-THIQ, which displayed excellent PNMT inhibitory potency. The rank order for selectivity (PNMT vs the alpha2-adrenoceptor) is 3-alkyl-7-aminosulfonyl-THIQs congruent with 3-alkyl-7-N-2,2,2-trifluoroethylaminosulfonyl-THIQs>3-alkyl-7-nitro-THIQs>3-alkyl-7-bromo-THIQs.

Binding Sites↗

PubMed2005

Conformational order of n-alkyl modified silica gels as evaluated by Fourier transform infrared spectroscopy.

The conformational behaviour of non-deuterated and selectively deuterated alkyl modified silica gels in the dry state is examined by variable temperature FT IR spectroscopy. In the present study, three systems are considered, which are distinguished by the length of the tethered alkyl chains (C9Hl9-, C18H37-, C22H45-). The desired information is obtained by the analysis of various conformational-sensitive IR bands, including CH2 wagging, CD2 stretching and CD2 rocking bands. The analysis of the CH2 wagging bands provides the relative amounts (i.e., integral numbers over the whole chain) of the kink/gauche-trans-gauche, double-gauche and end-gauche conformers in the tethered alkyl chains. From the analysis of the CD2 stretching and CD2 rocking bands information about the conformational order at a specific deuterated methylene segment is available. Here, the CD2 rocking band data are used to determine the amount of gauche conformers at the deuterated carbon positions C-4 and C-6, and C-12. It is found that the conformational order critically depends on the actual alkyl chain length, chain position and sample temperature. Particular emphasis is given to the impact of the external pressure during sample preparation on the alkyl chain conformations, about which so far no information is available. It is observed that the samples prepared as KBr pellets, which experienced a pressure of about 10 kbar, are characterised by a lower amount of gauche conformers. This substantial increase of conformational order is attributed to better alkyl chain packing along with a gain of intermolecular chain interactions.

Alkanes↗

PubMed1994

Studies of the thermotropic phase behavior of phosphatidylcholines containing 2-alkyl substituted fatty acyl chains: a new class of phosphatidylcholines forming inverted nonlamellar phases.

We have synthesized a number of 1,2-diacyl phosphatidylcholines with hydrophobic substituents adjacent to the carbonyl group of the fatty acyl chain and studied their thermotropic phase behavior by differential scanning calorimetry, 31P-nuclear magnetic resonance spectroscopy, and x-ray diffraction. Our results indicate that the hydrocarbon chain-melting phase transition temperatures of these lipids are lower than those of the n-saturated diacylphosphatidylcholines of similar chain length. In the gel phase, the 2-alkyl substituents on the fatty acyl chains seem to inhibit the formation of tightly packed, partially dehydrated, quasi-crystalline bilayers (Lc phases), although possibly promoting the formation of chain-interdigitated bilayers. In the liquid-crystalline state, however, these 2-alkyl substituents destabilize the lamellar phase with respect to one or more inverted nonlamellar structures. In general, increases in the length, bulk, or rigidity of the alkyl substituent result in an increased destabilization of the lamellar gel and liquid-crystalline phases and a greater tendency to form inverted nonlamellar phases, the nature of which depends upon the size of the 2-alkyl substituent. Unlike normal non-lamella-forming lipids such as the phosphatidylethanolamines, increases in the length of the main acyl chain stabilize the lamellar phases and reduce the tendency to form nonlamellar structures. Our results establish that with a judicious choice of a 2-alkyl substituent and hydrocarbon chain length, phosphatidylcholines (and probably most other so-called "bilayer-preferring" lipids) can be induced to form a range of inverted nonlamellar structures at relatively low temperatures. The ability to vary the lamellar/nonlamellar phase preference of such lipids should be useful in studies of bilayer/nonbilayer phase transitions and of the molecular organization of various nonlamellar phases. Moreover, because the nonlamellar phases can easily be induced at physiologically relevant temperatures and hydration levels while avoiding changes in polar headgroup composition, this new class of 2-alkyl-substituted phosphatidylcholines should prove valuable in studies of the physiological role of non-lamella-forming lipids in reconstituted lipid-protein model membranes.

Biophysical Phenomena↗

PubMed2000

Influence of the modification conditions of alkyl bonded ligands on the characteristics of reversed-phase liquid chromatography.

The parameters characterizing retention and the mass transfer mechanisms in reversed-phase liquid chromatography were derived from data acquired for a series of compounds on a silica gel bonded to alkyl ligands of various lengths and ligand densities. The adsorption equilibrium constant, the absolute value of the isosteric heat of adsorption, and the activation energy of surface diffusion increase while the surface diffusion coefficient decreases with increasing length of the alkyl chain and density of the C18 ligand. These results are consistent with increasing restriction of the mobility of an increasingly adsorbable molecule. There is a critical level of carbon content above which the four parameters just listed no longer change with increasing alkyl ligand density. This level is likely to depend on the sizes of the alkyl ligand and the sample molecule. Even at high densities of C18 chains, there may be a limitation in the contact area of the sample molecule and the alkyl ligand. The retention behavior on the stationary phases studied is explained by assuming that the sample molecules penetrate into the layer of alkyl ligands. Enthalpy-entropy compensation was demonstrated for surface diffusion. Its mechanism is probably similar on the different stationary phases studied, irrespective of the length and density of the bonded ligand.

Chromatography, Liquid↗

PubMed1987

Determination of alpha-alkyl-alpha-amino acids and alpha-amino alcohols by chiral-phase capillary gas chromatography and reverse-phase high-performance liquid chromatography.

The enantiomeric resolution by fused-silica capillary gas-liquid chromatography (GLC) of non-protein DL-alpha-alkyl-alpha-amino acids of the structure H2NCR1R2COOH (R1 = alkyl, R2 = alkyl, alkaryl) was investigated by using chiral [L-valine-tert.-butylamide, linked to a statistical polymer of dimethylsiloxane and (2-carboxypropyl)methylsiloxane, Chirasil-L-Val, and XE-60-S-Val-S-alpha-phenylethylamide] and non-chiral (methylphenylcyanopropylvinylpolysiloxane, CP-Sil-19 stationary phases. To evaluate the resolution coefficients, N-acylamino acid n-propyl esters (acyl = acetyl, propionyl, trifluoroacetyl, pentafluoropropionyl, heptafluorobutyryl) and diastereomeric esters with S(-)-2-methyl-1-butanol, S(+)-2-butanol and S(+)-2-octanol were used. Although alpha-alkyl-alpha-amino acids in general gave lower resolution coefficients than the enantiomers of protein amino acids, most alpha-alkyl-alpha-amino acids could be resolved by using suitable derivatization procedures and, preferably, isothermal conditions. In addition, a number of DL-alpha-alkyl-alpha-amino acids could be separated by ligand-exchange chromatography (L-hydroxyproline/Cu2+) by both thin-layer chromatography (Chiralplate) and high-performance liquid chromatography (HPLC) (Nucleosil Chiral-1). Further, a standard mixture composed of fifteen alpha-amino acids and eleven alpha-amino alcohols could be completely separated by C18 HPLC after derivatization with o-phthaldialdehyde-2-mercaptoethanol (OPA-2-ME). The time and temperature dependences of the relative fluorescence of the adducts were investigated kinetically.

Amino Acids↗

PubMed2003

Cytochrome c oxidase inhibition in the rice weevil Sitophilus oryzae (L.) by formate, the toxic metabolite of volatile alkyl formates.

Volatile alkyl formates are potential replacements for the ozone-depleting fumigant, methyl bromide, as postharvest insecticides and here we have investigated their mode of insecticidal action. Firstly, a range of alkyl esters, ethanol and formic acid were tested in mortality bioassays with adults of the rice weevil, Sitophilus oryzae (L.) and the grain borer, Rhyzopertha dominica (F.) to determine whether the intact ester or one of its components was the toxic moiety. Volatile alkyl formates and formic acid caused similar levels of mortality (LC(50) 131-165 micromol l(-1)) to S. oryzae and were more potent than non-formate containing alkyl esters and ethanol (LC(50)>275 micromol l(-1)). The order of potency was the same in R. dominica. Ethyl formate was rapidly metabolised in vitro to formic acid when incubated with insect homogenates, presumably through the action of esterases. S. oryzae and R. dominica fumigated with a lethal dose of ethyl formate had eight and 17-fold higher concentrations of formic acid, respectively, in their bodies than untreated controls. When tested against isolated mitochondria from S. oryzae, alkyl esters, alcohols, acetate and propionate salts were not inhibitory towards cytochrome c oxidase (EC 1.9.3.1), but sodium cyanide and sodium formate were inhibitory with IC(50) values of 0.0015 mM and 59 mM, respectively. Volatile formate esters were more toxic than other alkyl esters, and this was found to be due, at least in part, to their hydrolysis to formic acid and its inhibition of cytochrome c oxidase.

Animals↗

PubMed1994

Acylation of myelin basic protein peptide 1-21 with alkyl carboxylates 2-10 carbons long affects secondary structure and posttranslational modification.

A peptide consisting of the first 21 residues of human myelin basic protein (MBP) was synthesized. The N-terminal alanine of portions was blocked in separate experiments with alkyl carboxylates varying in size from 2 to 10 carbon atoms. The effects of these different alkyl carboxylates at the N-terminus on the secondary structure was studied by circular dichroism (250-190 nm). In water, the spectra of the unblocked peptide suggested unordered structure with large negative ellipticities at 198 nm. Addition of an acetyl group altered the magnitude of [theta]198 from -21856 +/- 2319 to -11095 +/- 1000 deg cm2 dmol-1, suggesting a significant increase in ordered structure. When peptides with longer alkyl carboxylates, acylated at the N-termini, were studied, the magnitude of theta 198 approached that of the unblocked peptide but greater negative ellipticities were observed for the C8 and C10 alkyl carboxylates. The theta 222 values were generally low (-1803 +/- 463) but increased with increasing length of the alkyl carboxylate to about -3200 deg cm2 dmol-1, suggesting that little alpha-helical structure was present. The spectra were also taken in lipid-mimetic solvents, including 2-propanol, methanol, and lysophosphatidylglycerol (lysoPG). In general the theta 198 and theta 222 values were suggestive of increased structure in these environments compared to water. In 90% 2-propanol the theta 198 of the unblocked peptide did not change when an acetyl group was added to the N-terminus (9088 compared to 8477 deg cm2 dmol-1). Addition of longer alkyl carboxylates correlated with larger, negative ellipticities.(ABSTRACT TRUNCATED AT 250 WORDS)

Acylation↗

PubMed1987

Sulfhydryl-alkylating reagents inactivate the NAD glycohydrolase activity of pertussis toxin.

The combination of ATP, CHAPS (3-[(3-cholamidopropyl)dimethylammonio]-1-propane-sulfonate), and DTT (dithiothreitol) is known to promote the expression of the NAD glycohydrolase activity of pertussis toxin, which resides in the toxin's S1 subunit. By monitoring changes in electrophoretic mobility, we have found that ATP and CHAPS act by promoting the reduction of the disulfide bond of the S1 subunit. In addition, ATP, CHAPS, and DTT allowed sulfhydryl-alkylating reagents to inactivate the NAD glycohydrolase activity. In the presence of iodo[14C]acetate, the combination of ATP, CHAPS, and DTT increased 14C incorporation into only the S1 subunit of the toxin, indicating that alkylation of this subunit was responsible for the loss of activity. If iodoacetate is used as the alkylating reagent, alkylation can be monitored by an acidic shift in the isoelectric point of the S1 peptide. Including NAD in alkylation reactions promoted the accumulation of a form of the S1 peptide with an isoelectric point intermediate between that of native S1 and that of S1 alkylated in the absence of NAD. This result suggests that NAD interacts with one of the two cysteines of the S1 subunit. In addition, we found the pH optimum for the NAD glycohydrolase activity of pertussis toxin is 8, which may reflect the participation of a cysteine in the catalytic mechanism of the toxin.

Adenosine Triphosphate↗

PubMed2004

C-terminus loop 13 of Na+ glucose cotransporter SGLT1 contains a binding site for alkyl glucosides.

Recently, we identified the extramembranous C-terminus loop 13 of SGLT1 as a binding site for the aromatic glucoside phlorizin, which competitively inhibits sodium D-glucose cotransport. Alkyl glucosides are also competitive inhibitors of the transport. Therefore, in this study, we searched for potential binding sites for alkyl glucosides in loop 13. To this end, we synthesized a photoaffinity label (2'-Azi-n-octyl)-beta-D-glucoside and analyzed the region of attachment using MALDI mass spectrometry, producing wild-type recombinant truncated loop 13. Furthermore, we prepared four single-Trp mutants of the loop and determined their fluorescence, its change in the presence of alkyl glucosides, and their accessibility to acrylamide. Photolabeling of truncated loop 13 with (2'-Azi-n-octyl)-beta-D-glucoside revealed an attachment of the C2 group of the alkyl chain to Gly-Phe-Phe-Arg (amino acid residues 598-601). In the presence of n-hexyl-beta-D-glucoside, all mutants (R601W, D611W, E621W, and L630W) exhibited a significant decrease in Trp fluorescence with an apparent binding affinity of 8-14 microM. Only L630W exhibited a significant blue shift, and only in R601W was a change in acrylamide quenching (protection) observed. No quenching or protection was found for D-glucose; however, 1-hexanol produced the same results as n-hexyl-beta-D-glucoside. The interaction shows stereoselectivity for n-hexyl-beta-D-glucoside binding; the beta-configuration of the sugar moiety at C1, the cis conformation of the unsaturated alkenyl side chain in the C3-C4 bond, and the alkyl chain length of six to eight carbon atoms lead to an optimum interaction. A schematic two-dimensional model was derived in which C2 interacts with the region around residue 601, C3 and C4 interact with the region between residues 614 and 619, and C6-C8 interact with the region between residues 621 and 630. The data demonstrate that loop 13 provides binding sites for alkyl glucosides as well as for phlorizin; thus, loop 13 of SGLT1 seems to be a major binding domain for the aglucone residues of competitive D-glucose transport inhibitors.

Acrylamide↗