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PubMed1982

Heat stability of milk: influence of modification of lysine and arginine on the heat stability-pH profile.

Several dicarbonyl compounds (glyoxal, substituted glyoxals, diacetyl and 1, 2-cyclohexanedione) had a marked stabilizing effect on the heat stability of milk, especially in the presence of urea. These reagents are believed to modify arginine more or less specifically suggesting an important role for arginine residues in heat stability. In contrast, modification of lysine residues with dansyl chloride, acetic anhydride or cyanoborohydride had little effect on maximum heat stability although it did alter the HCT-pH profile. Since diacetyl is a natural constituent of fermented milks and cheese, it may be acceptable as an additive to increase the heat stability of milk.

Acetic Anhydrides↗
PubMed2006

Comparative ligand-binding analysis of ten human lipocalins.

At least ten different lipocalins occur in the human body: retinol-binding protein (RBP), alpha1-acid glycoprotein, alpha1-microglobulin, apolipoprotein D, beta-trace protein, complement component 8gamma, glycodelin, neutrophil gelatinase-associated lipocalin, odorant-binding protein, and tear lipocalin. Although many of these lipocalins seem to play an important physiological role, their precise biological function is not always clear. Especially the interpretation of their diverse ligand-binding activities has been hampered by the fact that the natural lipocalins were prepared from different sources and with varying purity. Here we present a generic expression and purification strategy for the recombinant lipocalins, which is based on secretion into the periplasm of E. coli, where disulphide bonds are readily formed, followed by affinity purification via the Strep-tag II and gel filtration. The ten human lipocalins were successfully prepared and their ligand-binding activities were compared via fluorescence titration with a set of typical ligands: retinol, retinoic acid (RA), 11-(5-(dimethylamino)-1-naphthalene-sulfonylamino)undecanoic acid (DAUDA), and 8-anilino-1-naphtalene-sulfonic acid (ANS). As result, merely two lipocalins, RBP and beta-trace, revealed high affinities both for retinol and for RA, which probably reflects a specialized physiological function in retinoid complexation. Surprisingly, the strongest retinol affinity was detected for apolipoprotein D, whereas this lipocalin exhibits much weaker binding activity for retinoic acid. Binding studies with the two spectroscopic probes DAUDA and ANS revealed mixed patterns, which demonstrates that the affinity for lipophilic substances varies considerably among human lipocalins. Notably, RBP with its perfectly moulded retinol-binding site did not show any detectable binding activity for both compounds. Hence, our recombinant expression and purification system should be useful for further structural and functional studies of lipocalins from human origin and beyond.

Blood Proteins↗
PubMed1982

Adsorption of non-membrane proteins on the surface of model phospholipid membranes.

1. Two new methods are proposed for enhancement of the binding of hydrophilic proteins by liposomes. 2. An alkylating derivative of phosphatidic acid has been obtained by its reaction with N,N,N'-tris(2-chloroethyl)-N'-(p-formylphenyl)propylene-1,3-diamine. The alkylating activity of this derivative is very low due to the electron-acceptor effect of the formyl residue. Phosphatidylcholine liposomes which contain this alkylating derivative in the lipid bilayer may be obtained. The compound residing in the outer monolayer may be reduced by NaBH4. Upon reduction, the formyl residue is transformed into a hydroxymethyl residue. Therefore, the alkylating group of the compound is activated, and proteins may be attached covalently to the outer monolayer by alkylation with such chemically reactive liposomes. 3. Reaction of alkylating liposomes with myoglobin results in covalent binding of this hydrophilic protein. Complement-mediated leakage of such myoglobin-carrying liposomes may be induced by antibodies against myoglobin. 4. Modification of hydrophilic proteins with dansyl chloride results, even at small extents of modification, in a dramatic increase of the affinity of such proteins to phosphatidylcholine liposomes.

Adsorption↗
PubMed1990

Fluorescence postlabeling assay of cis-thymidine glycol monophosphate in X-irradiated calf-thymus DNA.

DNA damage was induced by irradiating calf-thymus DNA with a GE Maxitron-250 as an X-ray source. The use of nitrous oxide as a scavenger of solvated electrons in the irradiation process, resulted in essentially a monoreactant system of the biologically important hydroxyl radical. A novel approach combining the enzymatic digestion of the irradiated DNA to nucleoside 5' monophosphates and fluorescence postlabeling was applied to detect a specific modified nucleotide induced by ionizing radiation, namely the 5,6-dihydroxy-5,6-dihydrothymine lesion. This modification, often referred to as the glycol lesion, is polar and is generated mainly as the cis stereoisomers. In order to demonstrate the detection of this lesion in DNA by fluorescence labeling, the lesion was first produced chemically in a DNA model compound d(CGTA). The modified oligomers were isolated intact by HPLC and characterized by NMR as cis stereoisomers of glycol derivatives of d(CGTA). The major isomer of the modified d(CGTA) was enzymatically digested to yield 5' monophosphates. The digest was chromatographed by HPLC to enrich the modified nucleotide. The fraction containing the modified nucleotide was labeled with dansyl chloride. The fluorescent labeled nucleotide was chromatographed by HPLC. The same overall procedure was applied to DNA X-irradiated in aqueous solution. With a conventional fluorescence detector, HPLC analysis of the fluorescence labeled nucleotides detected 1 modified nucleotide/10(6) normal nucleotides from 100 micrograms DNA. The two cis glycol lesions were detected in the irradiated DNA by co-chromatography with fluorescent labeled markers. The initial assay of the modified oligomer demonstrated that the same stereoisomer of cis glycol was induced as a major modified nucleotide by both chemical oxidation and ionizing radiation.

Animals↗
PubMed2001

Hydraphile channels: models for transmembrane, cation-conducting transporters.

A completely synthetic, non-peptide channel has been prepared and shown to conduct cations across a phospholipid bilayer membrane. Studies have been undertaken to assess the compound's location within the bilayer and to better understand its function. These studies are described along with background on the design and concept of the channel.

Cations↗
PubMed2002

Photoactivated coumaryl-diazopyruvate fluorescent label for amine functional groups of tissues containing type-I collagen.

The design, synthesis and application of a new fluorescent-labeling reagent for collagen has been developed as a prerequisite for the design of a photoactivated collagen-crosslinking compound for surgical wound closure. The amine groups in collagen are the targets of a rational design for a new fluorophore because natural collagen crosslinks are formed between primary (1(o)) amine groups of lysine and hydroxylysine. The availability of 1(o) amines for crosslinking in native collagenous tissues was evaluated by reacting tendon and corneal samples with o-phthalaldehyde and dansyl chloride, fluorophores commonly used for the detection of 1(o) and 2(o) amines. The resulting fluorescent collagen fibrils indicated the presence of amines in native tissue. Subsequently, a photoactivated fluorescent label for 1(o) and 2(o) amines, coumaryl gamma-amino-butyric acid diazopyruvate (CGDP), was designed and synthesized. CGDP was first used to photolabel poly-L-lysine, forming a fluorescent, covalent bond to the 1(o) amine. CGDP was then photoreacted with corneal and tendon tissue samples to produce CGDP fluorescent-labeled samples that were statistically significantly more fluorescent than were the controls. These experiments support the postulate that 1(o) or 2(o) (or both) amines in native collagenous tissues are available to serve as targets for photoactivated collagen crosslinkers for wound closure.

Amines↗
PubMed1983

Co-accumulation of prephenate, L-arogenate, and spiro-arogenate in a mutant of Neurospora.

A mutant strain of Neurospora crassa blocked in each of the initial steps of tryptophan, tyrosine, and phenylalanine biosynthesis was previously shown to accumulate and secrete prephenate and L-arogenate (Jensen, R.A., Zamir, L.O., St. Pierre, M., Patel, N., and Pierson, D.L. (1977) J. Bacteriol. 132, 896-903). We now report the co-accumulation of yet another compound which was identified (Zamir, L.O., Tiberio, R., Jung, E., and Jensen, R.A. (1982) J. Biol. Chem. (1983) 258, 6486-6491) as the lactam derivative of L-arogenate. This structure, spiro-arogenate, undergoes a facile acid-catalyzed conversion to L-phenylalanine (as does L-arogenate). Since L-arogenate is conveniently quantitated as 5-dimethylaminonapthalene-1-sulfonyl (dansyl)-phenylalanine following acidification and dansylation, the unknown presence of spiro-arogenate may easily lead to overestimation of L-arogenate present in mixtures. Reliable quantitative assays for both L-arogenate and spiro-arogenate in mixtures were designed utilizing [3H]dansyl-chloride and exploiting the inability of the spiro-arogenate molecule to be dansylated in contrast to L-arogenate. The initial appearance of spiro-arogenate during accumulation lagged behind prephenate and L-arogenate, and spiro-arogenate accumulation leveled off after 5 days while prephenate and L-arogenate accumulations continued. It seems likely that spiro-arogenate is derived directly from L-arogenate. Prephenate, L-arogenate, and spiro-arogenate comprised about 70, 15, and 15% fractions of the total accumulation in a representative accumulation experiment designed to maximize spiro-arogenate yields. Modest variations in co-metabolite ratios were obtained under nutritional conditions where carbon source, growth temperature, duration of incubation time, and amino acid additions were experimental variables.

Amino Acids↗
PubMed1984

Binding of simple carbohydrates and some of their chromophoric derivatives to soybean agglutinin as followed by titrimetric procedures and stopped flow kinetics.

The number of carbohydrate-binding sites of the GalNAc-specific lectin is four per tetramer. The binding parameters of N-acetyl-D-galactosamine and methyl-N-acetyl-alpha-D- galactosaminide , were determined by titrating the perturbation in the absorption spectrum of the protein. For D-galactosides, it was necessary to use p-nitrophenyl-N-acetyl-beta-D- galactosaminide as an indicator in substitution titrations. The association constants K were determined at several temperatures yielding 2.4 X 10(4) M-1 at 25 degrees C with delta H degree' = -45 kJ mol-1 and delta S degree' = -67 J X K-1 mol-1 for methyl-N-acetyl-alpha-D- galactosaminide and 1.0 X 10(3) M-1 at 25 degrees C, delta H degree' = -38 kJ mol-1 and delta S degree' = -69 J X K-1 mol-1 for methyl-alpha-D-galactoside. The increase in K by a factor of 25 caused by the acetamido group is largely enthalpic . Whenever different methods were used to determine the association constant of a given compound, the agreement was excellent. The observed changes in absorption or fluorescence of all chromophoric carbohydrate derivatives used are specific for the binding of carbohydrates. For large aromatic beta- aglycons such as p-nitrophenyl or 4-methylumbelliferyl groups, the increase in K of the N-acetyl-D- galactosaminide moiety is by a factor of 2 or less, but for a large N-5-dimethylaminonaphthalene-1-sulfonyl (dansyl) group this factor is about 20 as compared with the acetyl group. The concomitant 10-fold increase in dansyl fluorescence, also observed with four other GalNAc-binding lectins together with a favorable and large delta S degree' = +60 J X K-1 mol-1 strongly point at the presence of a hydrophobic region in the vicinity of the carbohydrate-binding site. The results of stopped flow kinetics with 4-methylumbelliferyl-N-acetyl-beta-D- galactosaminide and the lectin are consistent with a simple mechanism for which k+ = 1.1 X 10(4) M-1 S-1 and k- = 0.4 S-1 at 25 degrees C. This k- is slower than for any monosaccharide-lectin complex reported so far.

Acetylgalactosamine↗
PubMed2001

Separation of amino acids, their derivatives and enantiomers by impregnated TLC.

The present state of TLC with respect to separation of amino acids, their different derivatives and their enantiomers by the technique of impregnation is discussed. The main approaches to impregnation viz. mixing of a suitable reagent with the adsorbent prior to plate-making, immersion of the untreated plate in the solution of impregnating reagent prior to development, and modification of the adsorbent, have been identified and discussed for each class of these compounds. The role of impregnation in resolving enantiomers or in improving the separation of mixtures of amino acids or their derivatives in terms of ion pairing, complex formation, ligand exchange or other steric interactions has been elaborated in each category.

Adsorption↗
PubMed1977

Energetics and molecular biology of active transport in bacterial membrane vesicles.

Bacterial membrane vesicles retain the same sidedness as the membrane in the intact cell and catalyze active transport of many solutes by a respiration-dependent mechanism that does not involve the generation of utilization of ATP or other high-energy phosphate compounds. In E. coli vesicles, most of these transport systems are coupled to an electrochemical gradient of protons (deltamuH+, interior negative and alkaline) generated primarily by the oxidation of D-lactate or reduced phenazine methosulfate via a membrane-bound respiratory chain. Oxygen or, under appropriate conditions, fumarate or nitrate can function as terminal electron acceptors, and the site at which deltamuH+ is generated is located before cytochrome b1 in the respiratory chain. Certain (N-dansyl)aminoalkyl-beta-D-galactopyranosides (Dns-gal) and N(2-nitro-4-azidophenyl)aminoalkyl 1-thio-beta-D-galactopyranosides (APG) are competitive inhibitors of lactose transport but are not transported themselves. Various fluorescence techniques, direct binding assays, and photoinactivation studies demonstrate that the great bulk of the lac carrier protein (ca. 95%) does not bind ligand in the absence of energy-coupling. Upon generation of a deltamuH+ (interior negative and alkaline), binding of Dns-gal and APG-dependent photoinactivation are observed. The data indicate that energy is coupled to the initial step in the transport process, and suggest that the lac carrier protein may be negatively charged.

Bacteria↗
PubMed1983

Sensitive and specific radioenzymatic assay for norepinephrine, epinephrine and dopamine based on the thin-layer chromatographic separation of their Dns-O-methyl derivatives.

A radioenzymatic assay is described in which norepinephrine, epinephrine and dopamine are converted to their tritiated 3-O-methyl derivatives by reaction with S-[methyl-3H]adenosyl-L-methionine in the presence of catechol-O-methyltransferase. The methylated compounds are then reacted with Dns chloride, and the Dns derivatives are extracted into ethyl acetate, isolated by thin-layer chromatography and quantified by liquid scintillation spectrometry. The assay displays a high degree of specificity for each compound, due in large part to the chromatographic properties of the Dns derivatives. It is capable of measuring 2 pg of each catecholamine, and is linear to at least 5 ng. Approximately 50 samples can be assayed in 1.5 days.

Animals↗
PubMed1981

Cycloheptaamylose-dansyl chloride complex as a fluorescent label of surface membranes in living ciliates.

Labelling of surface membrane of living ciliates: Paramecium aurelia and Tetrahymena pyriformis with fluorescent compound--cycloheptaamylose-dansyl chloride complex (CDC) has been achieved. Fluorescence micrographs of the dried samples showed specific localization of CDC on the cell membrane without any intracellular penetration. On the contrary the ciliates which have been dead during labelling revealed a non-specific fluorescence of their whole bodies. Microspectrofluorimetric analysis of labelled Paramecium cells was performed with Leitz microspectrograph. Spectrum of fluorescence emission measured over the cell membrane level had maximum at 450 nm. Strikingly, the emission maximum of the cells dead at the moment of labelling was shifted 10 nm to a longer wavelength. The rate of photofading measured in this case was almost 3-fold higher than for the ciliates labelled as living ones. Fluorescence excitation spectra did not show any difference in the peak position. Thus CDC staining appears to be an useful method of supravital labelling of cell surface enabling also to distinguish--on the basis of spectral characteristics--the ciliates being alive from those dead at the moment of fluorochrome binding.

Animals↗
PubMed2006

1H- and 13C-NMR, FTIR, UV-VIS, ESI-MS, and PM5 studies as well as emission properties of a new Schiff base of gossypol with 5-methoxytryptamine and a new hydrazone of gossypol with dansylhydrazine.

A new Schiff base of gossypol with 5-methoxytryptamine (GSTR) and a new hydrazone of gossypol with dansylhydrazine (GHDH) have been synthesized and studied by Fourier transform infrared (FTIR), 1H and 13C nuclear magnetic resonance (NMR), ultraviolet-visible (UV-VIS), electrospray ionization-mass spectroscopy (ESI-MS) as well as the parametric method PM5. The spectroscopic methods have provided clear evidence that GSTR exists in chloroform solution as an enamine-enamine tautomer, whereas GHDH is present in chloroform as a N-imine-N-imine tautomer. The fluorescence spectra of both compounds indicate that their quantum yield of fluorescence is increased by one or two orders of magnitude compared to that of pure gossypol. The ESI-MS spectra of the 1:1 mixtures of GSTR or GHDH with formic acid have demonstrated that both compounds exist as protonated monomers in the gas phase, whereas GHDH can also exist in a stable protonated dimeric structure. The structures of the stable tautomers are calculated and visualized using the PM5 semiempirical method. The intra- and intermolecular hydrogen bonds within these structures are discussed.

5-Methoxytryptamine↗
PubMed1997

New non-peptide endothelin-A receptor antagonists: synthesis, biological properties, and structure-activity relationships of 5-(dimethylamino)-N-pyridyl-,-N-pyrimidinyl-,-N-pyridazinyl-, and -N-pyrazinyl-1-naphthalenesulfonamides.

Use of automated synthesis led to the discovery of several 6-membered nitrogen heterocycles as replacements for the N-isoxazolyl substituent present in the 1-naphthalenesulfonamides endothelin-A (ETA) antagonist 5-(dimethylamino)-N-(3,4-dimethyl-5-isoxazolyl)-1-naphthalenesu lfo namides (BMS 182874). In each of these heterocycles, a small substituent such as halogen para to the position of attachment to the sulfonamide nitrogen atom was found to be advantageous for ETA receptor affinity. Of these heterocycles, 2-pyrazines offered the greatest scope for improving receptor affinity. Optimization of the substituents at the 3- and 5-positions in the pyrazine ring led to potent, ETA-selective compounds such as 5-(dimethylamino)-N-(5-chloro-3-methoxy-2-pyrazinyl)-1- naphthalenesulfonamides (7m, ETA pIC50 8.1). When dosed orally at 10 mg/kg to conscious, normotensive rats infused with big ET-1, compounds such as 7m showed significant inhibition of the pressor response with a duration of effect lasting for the 5-h course of the experiment.

Animals↗
PubMed1975

[Local anesthetic effect of several lipid-soluble compounds on the carbamylcholine response of the Electrophorus electroplax and the acetylcholine binding to the cholinergic receptor of Torpedo].

Several lipid soluble compounds: "Triton X-100", "Emulphogene BC-720" and 8-doxyl-palmitic acid behave-like local anesthetics on the in vivo response of Electrophorus electroplax to carbamylcholine and on the in vitro binding of 3-H acetylcholine to the membrane-bound cholinergic receptor from Torpedo.

Acetylcholine↗
PubMed2005

N-Acylhomoserine lactone quorum-sensing molecules are modified and degraded by Rhodococcus erythropolis W2 by both amidolytic and novel oxidoreductase activities.

The Rhodococcus erythropolis strain W2 has been shown previously to degrade the N-acylhomoserine lactone (AHL) quorum-sensing signal molecule N-hexanoyl-L-homoserine lactone, produced by other bacteria. Data presented here indicate that this Gram-positive bacterium is also capable of using various AHLs as the sole carbon and energy source. The enzymic activities responsible for AHL inactivation were investigated in R. erythropolis cell extracts and in whole cells. R. erythropolis cells rapidly degraded AHLs with 3-oxo substituents but exhibited relatively poor activity against the corresponding unsubstituted AHLs. Investigation of the mechanism(s) by which R. erythropolis cells degraded AHLs revealed that 3-oxo compounds with N-acyl side chains ranging from C8 to C14 were initially converted to their corresponding 3-hydroxy derivatives. This oxidoreductase activity was not specific to 3-oxo-AHLs but also allowed the reduction of compounds such as N-(3-oxo-6-phenylhexanoyl)homoserine lactone (which contains an aromatic acyl chain substituent) and 3-oxododecanamide (which lacks the homoserine lactone ring). It also reduced both the D- and L-isomers of n-(3-oxododecanoyl)-L-homoserine lactone. A second AHL-degrading activity was observed when R. erythropolis cell extracts were incubated with N-(3-oxodecanoyl)-L-homoserine lactone (3O,C10-HSL). This activity was both temperature- and pH-dependent and was characterized as an amidolytic activity by HPLC analysis of the reaction mixture treated with dansyl chloride. This revealed the accumulation of dansylated homoserine lactone, indicating that the 3O,C10-HSL amide had been cleaved to yield homoserine lactone. R. erythropolis is therefore capable of modifying and degrading AHL signal molecules through both oxidoreductase and amidolytic activities.

4-Butyrolactone↗