Detection of amino acids in artificial nectars by two tropical ants,Leptothorax and Monomorium

Summary Many ants forage at extrafloral nectar on plants and provide the plant with some measure of protection from herbivory. These nectars contain sugars, amino acids and, often, other compounds. The role of amino acids in attracting ants to extrafloral nectars was studied by baiting with Karo-syrup-based solutions. Control (without amino acids) and experimental (with amino acids) solutions were placed in second growth forest in Trinidad, W.I. The number of ants visiting the solutions was counted at fiveminute intervals for 45 min. In tests of solutions with only one amino acid, both Leptothorax sp. and Monomorium sp. visited solutions with alanine, arginine, serine, cysteine, methionine or aspartic acid more frequently than sugaronly controls. Monomorium preferred control solutions to tyrosine solutions; Leptothorax preferred control solutions to histidine solutions. Leptothorax did not discriminate between control and tyrosine solutions; Monomorium did not discriminate between control and histidine solutions. However, in six of eight tests of combinations of amino acids, ants visited control solutions more frequently than experimental solutions. These results suggest that ants can act as selective agents, favoring plants with particular amino acids in their nectars.     

Effect of organic and inorganic acids on concentrated chitosan solutions and gels

Rheological properties of concentrated chitosan aqueous solutions and gels in the presence of different organic and inorganic acids were investigated. Viscosities of the solutions increased with polymer concentration and degree of ionization. Strong gels were obtained at pH around 2 with oxalic, phosphoric and sulfuric acids. Gelation was favored by simple and short chain length acids and was governed by ionic interactions. The gels could be distinguished from solutions by the frequency independence of their dynamic moduli and their high apparent activation energy for flow.     

Polysulfone affinity membranes for the treatment of amino acid mixtures

Affinity membranes for the treatment of solutions containing amino acids were obtained via lithiating polysulfone that was subsequently converted with glycidylether. From this polymer asymmetric ultrafiltration membranes were cast. The membranes were reacted with iminodiacetic acid yielding membranes fitted out with bidentate chelates. The same reaction path was applied to commercially available symmetric microfiltration membranes. The chelate-bearing membranes were complexed with Cu, Ni, and Zn ions. For the experiments with amino acids only the Cu-complexed membranes were used. The complexation constants for histidine and tryptophan for six different membranes were determined. Because of the affinity of these two amino acids for the complexed Cu ions, they could easily be separated from solutions containing amino acids such as alanine, glycine, and valine. Also, concentrating very dilute amino acid solutions was carried out successfully. (c) 1995 John Wiley & Sons, Inc.     

Ion-pair extraction of bile acids with Lipidex gel

A new method for the extraction of bile acids from aqueous solutions, urine, plasma, and bile is described. A buffered solution of decyltrimethylammonium bromide is added to the sample to give a 0.03 m concentration of the counter-ion. The mixture is passed through a bed of Lipidex 1000, which is then washed with the buffered solution of counter-ion followed by water. The decyltrimethylammonium salts of bile acids are sorbed by the Lipidex and are eluted with methanol. Recoveries of unconjugated, taurine- and glycine-conjugated, sulfated, and glucuronidated bile acids are close to 100%. Unconjugated bile acids can also be quantitatively extracted from aqueous solutions and urine after acidification with acetic acid.     

Do Peacock butterflies (Inachis io L.) detect and prefer nectar amino acids and other nitrogenous compounds?

The preferences for nectar amino acids, urea and ammonium ions of peacock butterflies, Inachis io, were tested experimentally. Females clearly preferred a mimic of Lantana camara nectar containing amino acids to an otherwise similar plain sugar solution, whereas males did not discriminate between these test solutions. Neither males nor females discriminated between the full mixture of amino acids in a mimic of L. camara nectar and similar test solutions containing only the single amino acids arginine or proline. Furthermore, the butterflies were not able to detect methionine in the test solutions. Both sexes detected and preferred ammonium ions in test solutions but showed no response to urea. These results support the hypothesis that butterflies can select for high amino acid concentrations in floral nectar. However, it seems unlikely that they select for particular amino acids. The rather unspecific response of I. io males to the nectar constituents tested may result from their relatively low demand for nitrogen for spermatophore and sperm production, while their high activity may make energy supply (i.e. sugar) more important. The preference for ammonium ions suggests that I. io could also acquire nitrogen from ammonium-contaminated soil by puddling, as has been shown for sodium in swallowtail butterflies. Received: 15 August 1997 / Accepted: 14 September 1998     

Soluble macromolecular complexes involving bacterial teichoic acids.

Cell wall and membrane teichoic acids from several bacteria formed soluble complexes with polysaccharides and bovine plasma in alkyl alcohol solutions. Polysaccharides which contain different monomeric units and anomeric configurations complexed with the teichoic acids, suggesting that the interaction is relatively nonspecific. Teichoic acids complexed glycogen or bovine plasma albumin in 50 to 97% ethanol solutions. The macromolecular association between teichoic acids and polysaccharides or proteins was independent of teichoic acid size over a threefold molecular weight range. Glycerol phosphates or an acid hydrolysate of teichoic acid would not complex to either glycogen or bovine plasma albumin in ethanol. The optimal interaction between glycogen and the Bacillus subtilis lipoteichoic acid occurred between pH 4.5 and 8.2. The ability of teichoic acids to bind polysaccharides and proteins in moderate dielectric constant solvents suggests that these polymers may serve as complexing agents for hydrophilic molecules found in membranes.     

Single amino acids in sucrose rewards modulate feeding and associative learning in the honeybee

Obtaining the correct balance of nutrients requires that the brain integrates information about the body’s nutritional state with sensory information from food to guide feeding behaviour. Learning is a mechanism that allows animals to identify cues associated with nutrients so that they can be located quickly when required. Feedback about nutritional state is essential for nutrient balancing and could influence learning. How specific this feedback is to individual nutrients has not often been examined. Here, we tested how the honeybee’s nutritional state influenced the likelihood it would feed on and learn sucrose solutions containing single amino acids. Nutritional state was manipulated by pre-feeding bees with either 1 M sucrose or 1 M sucrose containing 100 mM of isoleucine, proline, phenylalanine, or methionine 24 h prior to olfactory conditioning of the proboscis extension response. We found that bees pre-fed sucrose solution consumed less of solutions containing amino acids and were also less likely to learn to associate amino acid solutions with odours. Unexpectedly, bees pre-fed solutions containing an amino acid were also less likely to learn to associate odours with sucrose the next day. Furthermore, they consumed more of and were more likely to learn when rewarded with an amino acid solution if they were pre-fed isoleucine and proline. Our data indicate that single amino acids at relatively high concentrations inhibit feeding on sucrose solutions containing them, and they can act as appetitive reinforcers during learning. Our data also suggest that select amino acids interact with mechanisms that signal nutritional sufficiency to reduce hunger. Based on these experiments, we predict that nutrient balancing for essential amino acids during learning requires integration of information about several amino acids experienced simultaneously.     

Calorimetric study of the interaction between amino acids and sugars in water at 298.15 K

The enthalpies of dissolving glycine and DL-alanine in water solutions of D-glucose, D-maltose, and sucrose at 298.15 K were determined by calorimetry. From the results obtained, the coefficients of enthalpy for pairwise interactions hxy of the amino acids and saccharides in water were calculated. It was found that the hxy values for glycine in solutions of all saccharides studied are negative; in the case of DL-alanine, the hxy values are positive for all saccharides except for sucrose solution. It was shown that the hxy values reflect the sum effect of interactions between the amino acids and saccharides in aqueous solutions and the contribution of hydration of the solutes.     

Influence of the glass packing on the contamination of pharmaceutical products by aluminium. Part II: Amino acids for parenteral nutrition

The presence of aluminium in amino acids parenteral nutrition solutions can be related to the affinity of the amino acids for aluminium present in glass containers used for storage. For this study solutions of 19 amino acids used in parenteral nutrition were stored individually in glass flasks and the aluminium measured at determined time intervals. Solutions of complexing agents for aluminium, as ethylene-diaminetetraacetic acid, nitrilotriacetic acid, citrate, oxalate and fluoride ions were also stored in the same flasks and the aluminium measured during the same time interval. The measurements were made by electrothermal atomic absorption spectrometry. The aluminium content of the glass containers was also measured. The results showed that the glasses have from 0.6% to 0.8% Al. Only solutions of cysteine, cystine, aspartic acid and glutamic acid became contaminated by aluminium. As the same occurred with the complexing agents, aluminum can be released from glass due to an affinity of the substances for aluminium. Comparing the action of complexing agents and amino acids for which the stability constants of aluminium complex are known, it is possible to relate the magnitude of the stability constant with the aluminium leached from glass, the higher the stability constant, the higher the aluminium released. The analysis of commercial formulations with and without cysteine, cystine, glutamic acid or aspartic acid stored in glass containers confirms that the presence of these amino acids combined with the age of the soLution are, at least partially, responsible for the aluminium contamination. The resuLts demonstrated that the contamination is an ongoing process due to the presence of aluminium in glass combined with the affinity of some amino acids for this element.     

Effects of low-molecular-weight organic acids on uptake of lanthanum by wheat roots

Effects of low-molecular-weight organic acids (LMWOAs) on the uptake of lanthanum by wheat (Triticum aestivum L.) roots were studied under hydroponic conditions. Acetic and malic acids were chosen as the representatives of LMWOAs. Uptake kinetics of lanthanum indicated that when lanthanum concentrations in the uptake solutions were high or uptake time was long lanthanum uptake by roots was enhanced by LMWAOs. After wheat was cultured in the uptake solution of lanthanum containing acetic or malic acids for 48 h the uptake of lanthanum by roots increased by 57 and 44%, respectively, compared with that in the absence of acetic and malic acids. The increase in uptake of lanthanum was determined by the ratio of the concentrations of organic acids to lanthanum in the uptake solutions. The highest uptake of lanthanum was obtained at the ratio of 5:1.     

Diffusion studies of bile acids,fatty acids and sucrose-NaCl-water systems at 37 °C by a modified capillary cell apparatus and their application to membrane transport studies

A capillary cell apparatus is described that allows accurate measurement of solute tracer diffusion coefficients in biological solutions at 37 °C. The apparatus has a unique stirring mechanism to provide a uniform flow pattern over the capillaries with only 18 ml of the bulk solution. Four capillaries of 2 cm length are used. With this apparatus measurement can be made at relatively short time periods so that bacterial overgrowth in the solutions is minimized. Using this apparatus tracer diffusion coefficients of three bile acids, cholic, taurochollic and taurodeoxycholic acids, and four fatty acids, acetic, pentanoic, octanoic and decanoic acids, were measured in an isotonic phosphate buffer, pH 7.1, at 37 °C. Viscosity, density and diffusion coefficients of sucrose in physiological saline solutions were also measured.     

Effect of calcium chloride on the conformation of proteins. Thermodynamic studies of some model compounds

Partial molar heat capacities (CP2 degrees) and volumes (V2 degrees) for some amino acids and peptides were measured in 1 M aqueous calcium chloride solutions at 298.15 degrees K using a Picker flow microcalorimeter and an oscillating-tube digital density meter. Using the data for these amino acids and peptides in water, the corresponding partial molar heat capacities of transfer (CP2,tr degree) and volumes (V2,tr degree) from water to 1 M aqueous calcium chloride were deduced. These thermodynamic parameters are significantly positive, indicating that strong interactions occur between the ions of calcium chloride and the charged centres of these amino acids and peptides. A comparison has been made with a similar transfer of these compounds to sodium chloride solutions. The thermodynamic parameters of the transfer of peptide group (-CONH) are much more positive in calcium chloride than in sodium chloride solutions. The implication of this result for the ability of calcium chloride to act as a stronger destabilizer of protein conformation is discussed.     

Transformation of some hydroxy amino acids to other amino acids.

It has been observed that beta-hydroxy-alpha-amino acids are transformed into other amino acids, when heated in dilute solutions with phosphorous acid, phosphoric acid or their ammonium salts. It has been shown that as in the case of previously reported glycine-aldehyde reactions, glycine also reacts with acetone to give beta-hydroxyvaline under prebiologically feasible conditions. It is suggested, therefore, that the formation of beta-hydroxy-alpha-amino acids and their transformation to other amino acids may have been a pathway for the synthesis of amino acids under primitive earth conditions.     

Carbonic anhydrase inhibitors: synthesis of water soluble sulfonamides incorporating a 4-sulfamoylphenylmethylthiourea scaffold,with potent intraocular pressure lowering properties

Reaction of thiophosgene with 4-aminomethyl-benzenesulfonamide afforded 4-isothiocyanatomethyl-benzenesulfonamide, which by reaction with amines, amino acids and oligopeptides, lead to a series of new sulfonamides incorporating a 4-sulfamoylphenylmethylthiourea scaffold. These new thioureas showed strong affinities towards isozymes I, II and IV of carbonic anhydrase (CA, EC 4.2.1.1). In vitro inhibitory potency was good (in the low nanomolar range) for the derivatives of: amino-benzoic acids, beta-phenyl-serine, alpha-phenyl-glycine, for those incorporating hydroxy- and mercapto-amino acids (Ser, Thr, Cys and Met), hydrophobic amino acids (Val, Leu, Ile), aromatic amino acids (Phe, His, Trp, Tyr; DOPA); dicarboxylic amino acids as well as di-/tri-/tetrapeptides among others. Such CA inhibitors displayed very good water solubility (in the range of 2-3%) as sodium (carboxylate) salts, with pH values for the solutions obtained of 6.5-7.0. Furthermore, in normotensive rabbits, some of them showed an effective and prolonged intraocular pressure (IOP) lowering when administered topically, as 2% solutions.     

Chemical stimulation of Schistosoma mansoni miracidial activity.

The movements of S. mansoni miracidia immersed in various solutions of organic chemicals were recorded by dark ground photography. Reduction of miracidial speed was recorded for miracidia in solutions of fatty acids and ammonia. The speed reduction was concentration dependant and pH dependant, indicating in both cases that the un-ionized molecule was responsible. Ammonia at concentrations between 0.4 mM and 0.8 mM elicited an increased "rate of change of direction" by miracidia. No changes in miracidial movements were recorded for miracidia immersed in aqueous solutions of amino acids, sugars or of molluscan nitrogenous excretion products other than ammonia. A possible role for chemo-klinokinetic behaviour patterns in miracidial host location was formulated.     

Emission spectra from copper proteins containing type-3 centres

Aqueous solutions of copper-proteins containing type-3 centres (ceruloplasmin, tyrosinase, haemocyanin), excited within their absorption bands at 325-345 nm, show typical luminescence spectra. The emission bands peak at 415-445 nm and their decay time is no longer than 10 ns. A strong analogous fluorescence is obtained also by excitation of concentrated solutions of carboxylic acids and amino acids, which show again absorption bands around 330 nm. Such a fluorescence, although less intense, is also observed in copper(II) carboxylate solutions. In contrast, no fluorescence has been recorded in solutions of acetic anhydride and of polypeptides (valinomycin, gramicidin D), which do not have free carboxyl groups. We tentatively attribute this novel fluorescence in the investigated copper proteins to interactions between carboxyl groups of amino acids at, or near, the active site.     

Carbonic Anhydrase Inhibitors: Synthesis of Water Soluble Sulfonamides Incorporating a 4-sulfamoylphenylmethylthiourea Scaffold,with Potent Intraocular Pressure Lowering Properties

Reaction of thiophosgene with 4-aminomethyl-benzenesulfonamide afforded 4-isothiocyanatomethyl-benzenesulfonamide, which by reaction with amines, amino acids and oligopeptides, lead to a series of new sulfonamides incorporating a 4-sulfamoylphenyl-methylthiourea scaffold. These new thioureas showed strong affinities towards isozymes I, II and IV of carbonic anhydrase (CA, EC 4.2.1.1). In vitro inhibitory potency was good (in the low nanomolar range) for the derivatives of: amino-benzoic acids, β -phenyl-serine, α -phenyl-glycine, for those incorporating hydroxy- and mercapto-amino acids (Ser, Thr, Cys and Met), hydrophobic amino acids (Val, Leu, Ile), aromatic amino acids (Phe, His, Trp, Tyr; DOPA); dicarboxylic amino acids as well as di-/tri-/tetrapeptides among others. Such CA inhibitors displayed very good water solubility (in the range of 2-3%) as sodium (carboxylate) salts, with pH values for the solutions obtained of 6.5-7.0. Furthermore, in normotensive rabbits, some of them showed an effective and prolonged intraocular pressure (IOP) lowering when administered topically, as 2% solutions.     

Influence of the glass packing on the contamination of pharmaceutical products by aluminium. Part III: Interaction container-chemicals during the heating for sterilisation

The interaction of chemicals with the container materials during heating for sterilisation was investigated, storing the components of parenteral nutrition solutions individually in sealed glass ampoules and in contact with a rubber stopper, and heating the system at 121 degrees C for 30 min. Subsequently, the aluminium content of the solutions was measured by atomic absorption spectrometry (AAS). The assay was also carried out with acids, alkalis and some complexing agents for Al. The containers were decomposed and also assayed for aluminium. 30 different commercial solutions for parenteral nutrition, stored either in glass or in plastic containers, were assayed measuring the aluminium present in the solutions and in the container materials. The results of all investigated container materials revealed an aluminium content of 1.57% Al in glass, 0.05% in plastic and 4.54% in rubber. The sterilisation procedure showed that even pure water was able to extract Al from glass and rubber, 22.5 +/- 13.3 microg/L and 79.4 +/- 22.7 microg/L respectively, while from plastic the aluminium leached was insignificant. The Al released from glass ampoules laid between 20 microg/L for leucine, ornithine and lysine solutions and 1500 microg/L for solutions of basic phosphates and bicarbonate; from rubber stoppers it reached levels over 500 microg/L for cysteine, aspartic acid, glutamic acid and cystine solutions. Ion-exchange properties and influence of pH can explain the interaction of glass with some chemicals (salts, acids and alkalis), but only an affinity for aluminium could explain the action of some amino acids and other chemicals, as albumin and heparin, on glass and rubber, considering the aluminium release. Experiments with complexing agents for Al allowed to conclude that the higher the stability constant of the complex, the higher the Al release from the container material.     

Antimicrobial films produced from chitosan.

Antimicrobial films were prepared by dissolving chitosan into hydrochloric, formic, acetic, lactic and citric acid solutions. Below 40 degrees C, the counter ions could be classified into two groups based on their effect on zero-shear-rate viscosity in 2% solutions of organic acids. Chloride and citrate produced solutions with much lower viscosities than formate, acetate and lactate. At higher temperatures, these differences vanished, and the activation energies of viscous flow were all similar between 40 and 60 degrees C. Films prepared from these solutions were evaluated in tension for Young's modulus, stress and elongation at yield and break points. Films made from hydrochloric, formic and acetic acids were hard and brittle, whereas those from lactic and citric acids were soft and could be stretched. Good correlation was found between Young's modulus and volume of the counter ion. Film properties are essentially governed by the volume of the counter ion and not by the interactions between this counter ion and the macromolecule. Results suggest that acetate has the maximum molecular volume above which the film strength decreases very rapidly.     

Cell culture models of fatty acid overload: Problems and solutions

High plasma levels of fatty acids occur in a variety of metabolic diseases. Cellular effects of fatty acid overload resulting in negative cellular responses (lipotoxicity) are often studied in vitro, in an attempt to understand mechanisms involved in these diseases. Fatty acids are poorly soluble, and thus usually studied when complexed to albumins such as bovine serum albumin (BSA). The conjugation of fatty acids to albumin requires care pertaining to preparation of the solutions, effective free fatty acid concentrations, use of different fatty acid species, types of BSA, appropriate controls and ensuring cellular fatty acid uptake. This review discusses lipotoxicity models, the potential problems encountered when using these cellular models, as well as practical solutions for difficulties encountered.