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PubMed1999

Molecular dynamics simulation of double proton transfer: adenine-thymine base pair.

Molecular dynamics of proton transfer was simulated from normal (N) to tautomeric (T) form of the base pair (bp) adenine-thymine (A-T). The results for the model system, consisting of one A-T base pair in SPC/E water, was analysed in terms of its hydration properties, difference on free energy, conformational changes, and magnetic properties. It is suggested that during proton transfer the base pair remains on the same conformational state. The free energy of the protons transfer appears to be almost insensitive to the presence of water. The overall hydrophobicity of the A-T pairs is slightly modified by the proton transfer the N form being a little more hydrophobic. The behavior of the magnetic shielding suggests that a current is produced in the ring of the hydrogen bonds due to strong pi -electron delocalization in the amide-amidine complex.

Adenine↗
PubMed1986

Arginyl residues and thermal stability in proteins.

Guanidination and amidination of bovine serum albumin, yeast enolase and yeast alcohol dehydrogenase were accompanied by increases in thermal stability at lower extents of modification. Decreases in thermal stability result from greater modification. These results support suggestions that surface guanidino groups (arginyl groups) are an important factor in thermal stability of proteins.

Alcohol Dehydrogenase↗
PubMed1991

Pheromone/acaricide mixtures in the control of the tick Amblyomma hebraeum: effects of acaricides on attraction and attachment.

Unfed adults and nymphs of the bont tick Amblyomma hebraeum Koch are attracted to hosts on which fed males, emitting an aggregation-attachment pheromone (AAP), are attached. Pheromone/acaricide mixtures have the potential to selectively attract and kill these ticks. We have investigated the effects of three acaricides, amitraz (an amidine), flumethrin (a synthetic pyrethroid) and chlorfenvinphos (an organophosphate), combined with AAP, on the attraction and attachment of the unfed adults. Attraction, measured in field assays involving AAP and CO2, was not inhibited by any of the acaricides. Attachment was measured over 24 h on the ears of rabbits which had been treated with AAP and mixtures of AAP and the acaricides. None of the acaricides inhibited initial attachment. Flumethrin caused rapid and high mortality in attached and unattached ticks. Chlorfenvinphos caused little mortality in the first 24 h on the ears of the rabbits, but 75% of the exposed ticks died over the next 14 days while held in an incubator. Amitraz caused the ticks to detach after an initial period of attachment; there was little mortality in the detached ticks over the next two weeks and they could later be induced to re-attach to other rabbits. Flumethrin was considered to be the compound of choice for use in pheromone/acaricide mixtures.

Animals↗
PubMed1986

The chemistry of lipid peroxidation metabolites: crosslinking reactions of malondialdehyde.

Malondialdehyde reacts readily with amino acids to form adducts containing vinylogous amidine linkages. Crosslinking reactions between nucleic acid bases and amino acids induced by malondialdehyde also have been investigated. The physical data obtained for the adducts provide structural information on the possible mode of crosslinking of proteins and nucleic acids induced by this lipid metabolite.

Chemical Phenomena↗
PubMed1993

Experimental chemotherapy of filariasis: comparative evaluation of the efficacy of filaricidal compounds in Mastomys coucha infected with Litomosoides carinii, Acanthocheilonema viteae, Brugia malayi and B. pahangi.

Eleven types/classes of compound with antifilarial activity were comparatively evaluated in Mastomys coucha infected with Litomosoides carinii, Acanthocheilonema viteae, Brugia malayi or B. pahangi. The paper deals with the efficacy of (i) predominantly microfilaricidal compounds [diethylcarbamazine, levamisole, avermectins (ivermectin, milbemycin), nitrofurans (nitrofurantoin, hydroxymethylnitrofurantoin, nifurtimox, furazolidone, furapyrimidone), organophosphorals (metrifonate, haloxon), and aminophenyl-amidines], (ii) predominantly macrofilaricidal compounds [suramin, benzimidazoles (flubendazole, mebendazole, oxfendazole, ciclobendazole, albendazole, cambendazole, fenbendazole), and arsenicals (thiacetarsamide, Mel PH, R7/45)], and (iii) micro- and macrofilaricidal compounds [benzazole derivatives (CGP 20376 and other benzothiazoles) and nitrophenylamines (amoscanate, CGP 6140)]. Minimum effective doses against microfilariae and minimum curative doses against adult filariae as well as detailed data on dose-efficacy relationships are reported for the various drugs. The results obtained in M. coucha are compared with those published for other experimental in vivo filarial systems, thus attempting to describe a general status of in vivo antifilarial activity of the compounds.

Animals↗
PubMed1990

Separation and quantitation of the polyamine biosynthesis inhibitor D,L-alpha-difluoromethylarginine and other guanidine-containing compounds by high-performance liquid chromatography.

The arginine decarboxylase inhibitor difluoromethylarginine (DFMA) is an important tool in the study of polyamine metabolism, particularly with respect to the human pathogen Trypanosoma cruzi. This paper demonstrates a unique method for the detection and quantitation of intracellular DFMA using the fluorogenic agent 9,10-phenanthrenequinone. After separation of cell extracts by HPLC, DFMA can be accurately and reproducibly quantified with a lower sensitivity limit of 0.1 nmol by this simple fluorometric method. This assay can also be used to detect other guanidine-containing compounds such as arginine, agmatine, creatinine, and hirudonine, but not substituted guanidines such as aminoguanidine and creatine, or the structurally related amidines such as benzamidine and pentamidine.

Animals↗
PubMed1988

The bacteriorhodopsin proton pump: effect of crosslinkings of lysine residues.

All six available lysine residues in bacteriorhodopsin were amidinated with dimethyl-3,3'-dithiobispropionimidate, which is a crosslinking agent. The photocycle was studied by measuring light absorption and electric signals. The data show an essential change in the photocycle: instead of single components, the rise of the signal due to the M intermediate can be decomposed into two components, and the decay into three. The life-times and the intensities of these components and in general the proton pumping activity of bacteriorhodopsin depend only negligibly upon pH. Changes upon removing the crosslinks are not significantly different from those in the crosslinked samples. The lysine residues therefore may not be considered of primary importance in proton translocation.

Bacteriorhodopsins↗
PubMed1980

Photosensitized cross-linking of erythrocyte membrane proteins. Evidence against participation of amino groups in the reaction.

Exposure of human erythrocyte ghosts (pH 8, 10 degrees C) to visible light in the presence of the photosensitizer, methylene blue, results in a relatively rapid loss of spectrin (bands 1 and 2 on sodium dodecyl sulfate gel electropherograms) and the appearance of high molecular weight cross-linked derivatives. Isolated spectrin also undergoes photosensitized cross-linking, indicating that the reaction is not lipid-dependent. Extensive cross-linking was neither reversed by dithiothreitol nor prevented by prior blocking of SH groups with N-ethylmaleimide, suggesting that cysteine residues are not crucial bridging sites. The possible requirement for NH2 groups, as suggested by previous model studies (Dubbelman, T.M.A.R., de Goeij, A.F.P.M. and van Steveninck, J. (1978) Biochim. Biophys. Acta 511, 141--151), was tested. Succinylation of spectrin protected against cross-linking, but this effect is attributed to the disruption of quaternary structure, as deduced from sedimentation measurements. However, virtually complete blocking of NH2 groups by amidination perturbed overall structure relatively little, and had no effect on cross-linking. Moreover, exogenous amines such as ethylamine, added in large excess to spectrin prior to irradiation, did not interfere with cross-link formation. These results suggest that NH2 groups are not involved in the reaction.

Cross-Linking Reagents↗
PubMed1981

Photodynamic protein cross-linking.

Exposure of spectrin to visible light in the presence of a photosensitizer results in photo-oxidation of sensitive amino acid residues and covalent cross-linking of the polypeptides. In a previous paper the cross-linking was ascribed to a secondary reaction between photo-oxidized histidine residues and amino groups. The following observations, described in this paper, are in accordance with this supposition. (1) During illumination of spectrin in the presence of a photosensitizer a pronounced photo-oxidation of histidine residues takes place. (2) Simultaneously a decrease of free amino groups is observed. (3) Semicarbazide protects against cross-linking and is bound to a histidine photo-oxidation product in spectrin. (4) The pH profile of histidine photo-oxidation and subsequent reaction with amino groups is similar to the pH profile of spectrin cross-linking. Amidination of NH2 groups in spectrin does not inhibit cross-linking, as visualized by gel electrophoresis. On the other hand aminidation of denatured myoglobin causes a 50% inhibition of cross-linking. These observations support the notion of NH2-involvement in cross-linking but also demonstrate, that other photodynamic cross-link mechanisms exist.

Amino Acids↗
PubMed1989

Cross-linking of phosphatidylethanolamine neighbors with dimethylsuberimidate is sensitive to the lipid phase.

Dimethylsuberimidate was reacted with aqueous dispersions of dipalmitoylphosphatidylethanolamine, dimyristoylphosphatidylethanolamine, dilauroylphosphatidylethanolamine, and dielaidoylphosphatidylethanolamine at pH 10 and at pH 8. The amount of amidine dimer formation was about four times greater above the gel-to-fluid phase transition of each lipid than below the transition. The transition temperature of each phosphatidylethanolamine, measured by steady-state fluorescence anisotropy of cis-parinaric acid, was lower at pH 10 than at pH 8 or in water. The ability of dimethylsuberimidate to discriminate between phosphatidylethanolamines in the fluid and gel phases should allow use of this reagent to identify phosphatidylethanolamine species within the gel or fluid lipid phase.

Cross-Linking Reagents↗
PubMed1981

Importance of the N-terminal sequence in porcine pancreatic colipase.

Colipase exists in pancreatic juice in a pro-form which is activated by limited trypsin hydrolysis. During this activation, the N-terminal pentapeptide 1Val-Pro-Asp-Pro-5Arg is cleaved. The new N-terminal sequence formed, 6Gly-Ile-Ile-Ile-10Asn, contains three isoleucine residues. The importance of these for stimulating lipase activity has been investigated by successive Edman degradation of epsilon-acetimidolysine residues followed by limited trypsin hydrolysis. The epsilon-amidinated colipase obtained was fully active both with a phospholipid-covered triacylglycerol (Intralipid) and tributyrin as substrate. After removal of the three isoleucine residues, the activity of colipase was lost with Intralipid but not with tributyrin as substrate. The shortened colipases regained their Intralipid activity upon addition of long-chain fatty acids. The binding of colipase to lipase was not affected by removal of the isoleucine residues.

Amino Acid Sequence↗
PubMed1992

Inhibition of enzymes of polyamine back-conversion by pentamidine and berenil.

Pentamidine and berenil, clinical antiparasitic amidines, have been found to be potent competitive inhibitors of human spermidine/spermine acetyltransferase (SSAT). Ki values were found to be 2.4 and 2 microM, respectively, with spermidine as substrate. A second enzyme of polyamine back-conversion, murine polyamine oxidase (PAO), was found to be competitively inhibited by pentamidine, with a Ki of 7.6 microM when N-acetylspermine was the substrate. Berenil, on the other hand, was an extremely weak inhibitor (Ki = 120 microM). The implication of the effect of inhibition of polyamine back-conversion on the growth of mammalian parasites is discussed.

Acetyltransferases↗
PubMed1991

Fluoro-Gold: composition, and mechanism of uptake.

Determining the mechanism by which fluorescent retrograde neuronal tracers are taken up requires knowledge of their composition. It has been claimed that Fluoro-Gold, a retrogradely transported fluorescent neuronal tracer, is 2-hydroxy-4,4'-diamidinostilbene (hydroxystilbamidine), an amidine antibiotic. However, this appears questionable, since the fluorescence spectrograms reported for Fluoro-Gold differ markedly from the spectrograms previously reported for purified hydroxystilbamidine. To help clarify the mechanism by which Fluoro-Gold might be taken up, it was decided to examine its composition and determine whether hydroxystilbamidine was its active agent. Fluoro-Gold was found by mass spectrometry to contain a component with a molecular weight of 280 Da (identical to that of hydroxystilbamidine), and fluorescence spectroscopy demonstrated the existence of a substance with a fluorescence spectrum similar to that of purified hydroxystilbamidine. Although a major fluorescent impurity was also observed, chromatographic separation of different fluorescent components of Fluoro-Gold suggested that the fraction resembling hydroxystilbamidine was responsible for its retrograde labeling of cells. It is concluded that hydroxystilbamidine is the active constituent of Fluoro-Gold. Chemically, hydroxystilbamidine is a weak base. In this respect it resembles True blue, DAPI, Granular blue, bis-benzimide, Nuclear yellow, and several other retrogradely transported molecules. It is suggested that these agents cross cell membranes in their uncharged form and are trapped in lysosomes and endosomes by a favorable pH gradient. Thus, the uptake of this type of retrograde tracer may be an example of a well-understood process occurring widely throughout biological systems: the trapping of weak bases in acidic cellular compartments.

Animals↗
PubMed1978

Cross-linking of membrane phospholipid and protein using putative monofunctional imidoesters.

The reaction of methyl acetimidate or isethionyl acetimidate with mitoplasts at pH 8.5 yields two derivatives of phosphatidylethanolamine. These derivatives are shown to be the mono-amidine derivative and the bis-derivative of phosphatidylethanolamine. The bis-derivative represents one phosphatidylethanolamine cross-linked to another phosphatidylethanolamine. Similar derivatives are formed by the reaction of dipalmitoyl phosphatidylethanolamine with these imidoesters in organic solution with the exception that much more monoderivative is produced. Methyl picolinimidate reacts with phosphatidylethanolamine of mitoplasts to form primarily the mono-derivative. The bis-derivative was not detected. The reaction of bovine rod outer segment discs with methyl acetimidate causes cross-linking of 30% of the membrane rhodospin as dimers. Putative monofunctional imidoesters cause considerable cross-linking of both phospholipids and proteins in cell membranes. Cross-linking can be minimized at pH 9.0.

Animals↗
PubMed1989

Analysis of dimeric species derived from the reaction of phosphatidylethanolamine with dimethylsuberimidate.

Phosphatidylethanolamines of various fatty acyl species in vortexed lipid dispersions were reacted with dimethylsuberimidate to produce dimeric products. The yield was 34% at pH 10 and 2% at pH 7. The crosslinked phosphatidylethanolamine species were separated from minor products and the reactants by extraction and two-dimensional thin-layer chromatography on silica gel G, gel filtration on lipophilic Sephadex, or C18-reversed phase high-performance liquid chromatography (HPLC). Reversed phase HPLC was also used to resolve the dimers into individual molecular species. Analysis of the dimers revealed the extinction coefficients at 205 nm to be higher than those of the reactant phosphatidylethanolamines. Proton nuclear magnetic resonance spectroscopy and chemical analysis implied that the dimers contain an amidine group.

Chemical Phenomena↗
PubMed1991

Stabilization of clathrin coated vesicles by amantadine, tromantadine and other hydrophobic amines.

Amantadine and related compounds stabilized the structure of purified pig brain clathrin coated vesicles (CCV) at biologically relevant concentrations. Incubation of purified CCV for 30 min at 25 degrees C or 37 degrees C caused the release of clathrin, as determined by a centrifugation assay, and a reduction in the number of coated vesicles, by electron microscopy. Amantadine (10 mM), tromantadine (1 mM), amidine D295 (cyclohexylcarboximidamide-(N-benzyl)hydrochloride (10 mM), chloroquine (0.1 mM) and monodansylcadaverine (10 mM) significantly reduced the extent of dissociation.

Amantadine↗
PubMed1979

Hapten-sandwich labeling. IV. Improved procedures and non-cross-reacting hapten reagents for double-labeling cell surface antigens.

New procedures are presented for preparation of hapten-antibody conjugates with the bifunctional amidinating reagent methyl-p-hydroxybenzimidate (HB). Conjugates with improved solubility are effective for hapten-sandwich labeling of cell surface antigens with high sensitivity and specificity. Several non-cross-reacting hapten-antihapten antibody systems are described which are well-suited for simultaneous labeling of different surface antigens.

Animals↗
PubMed1984

Heterotypic tetramer (A2D2) complexes of non-epidermal keratins isolated from cytoskeletons of rat hepatocytes and hepatoma cells.

Cytoskeletal residues obtained after extraction of rat liver and cultured rat hepatoma cells (line MH1C1) were used to isolate cytokeratin subunit complexes by solubilization in low salt buffer containing 4 M-urea. Alternatively, the complexes were prepared by solubilization of total cytoskeletal proteins in 9.5 M-urea or 6 M-guanidinium hydrochloride (Gu . HCl), followed by separation using reversed phase high pressure liquid chromatography and dialysis first against either 9.5 M-urea or 6 M-Gu . HCl and then against buffers containing either 4 M-urea or 2 M-Gu . HCl, respectively. The complexes contained only two cytokeratin polypeptides in a 1 : 1 ratio as demonstrated by electrophoresis and isoelectric focusing, i.e. components A (Mr 55,000; isoelectric point in 9.5 M-urea, pH 6.4) and D (Mr 49,000; isoelectric point, pH 5.38) which were separated from each other at urea concentrations higher than 7 M. The complex had a sedimentation coefficient S25,w of 4.96 S in 2 M-Gu . HCl. Sedimentation equilibrium analysis gave an average Mr value of 207,000 which was interpreted as a tetramer containing two chains each of A and D. This complex was also directly demonstrated by gel electrophoresis under non-dissociating conditions. Using dimethyl suberimidate to cross-link the complex in solution of 4 M-urea or 2 M-Gu . HCl, we identified covalently linked heterodimers of A and D, and a tetrameric unit containing equal amounts of A and D which was the largest cross-link product obtained. This complex was similar to the tetrameric complex of rat and human vimentin formed under the same conditions. The constituents of the cross-linked products were identified by two-dimensional ("diagonal") gel electrophoresis, involving the cleavage of the bis(amidine) cross-links after the initial separation in the first dimension. Identical cross-link products were recognized when cytokeratin filaments were used. By electron microscopy the complexes appeared as threads of 2 to 3 nm diameter with a mean length of approximately 48 nm. On dialysis to low salt buffer, the complexes formed 2 to 3 nm protofilaments, intertwisted 3 to 4 nm protofilaments and typical 7 to 11 nm intermediate-sized filaments. Complexes formed from equivalent cytokeratins of other species such as man and cow, as well as heterologous recombinations such as human component A mixed with bovine component D and vice versa, showed the same characteristics.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗