Effect of amino acids on acrylamide formation and elimination kinetics

The effect of amino acids other than asparagine on acrylamide (AA) formation/elimination kinetics was studied in an asparagine-glucose model system (0.01 M, pH 6) heated at temperatures between 140 and 200 degrees C. Addition of cysteine or lysine to the model significantly lowered the AA yield, whereas addition of glutamine had a strong promoting effect and of alanine a rather neutral effect on the AA formation. This was also reflected by AA formation/elimination kinetics, which for all model systems studied could be modeled by two consecutive first-order reactions. The ratio of the elimination to the formation rate constant increased from the systems to which glutamine or alanine was added, over the control model system, to the model systems that contained lysine or cysteine.     

Observations on the elimination of water from 2-hydroxy acids in the metabolism of amino acids by Clostridium sporogenes

Cell-free extracts of Clostridium sporogenes catalyse the water elimination from (2R)-phenyllactate in the presence of one of the energy-rich compounds acetyl-CoA, acetylphosphate or ATP and coenzyme A. Water is eliminated from (2R)-phenyllactoyl-CoA without any of the aforementioned additions. Cinnamoyl-CoA also acts catalytically. One molecule of cinnamoyl-CoA causes the elimination of water from more than 8 molecules phenyllactate. This is important from an energetic point of view since less than 2 mol ATP are formed per 2-3 mol metabolized amino acids. An activation of the hydroxy group of the alpha-hydroxy acid in form of a phosphate ester can also be excluded for energetic reasons.     

Transformation of metals and metal ions by hydrogenases from phototrophic bacteria

The ability of hydrogenases isolated from Thiocapsa roseopersicina and Lamprobacter modestohalophilus to reduce metal ions and oxidize metals has been studied. Hydrogenases from both phototrophic bacteria oxidized metallic Fe, Cd, Zn and Ni into their ionic forms with simultaneous evolution of molecular hydrogen. The metal oxidation rate decreased in the series Zn>Fe>Cd>Ni and depended on the pH. The presence of methyl viologen in the reaction system accelerated this process. T. roseopersicina and L. modestohalophilus cells and their hydrogenases reduced Ni(II), Pt(IV), Pd(II) or Ru(III) to their metallic forms under H₂ atmosphere. These results suggest that metals or metal ions can serve as electron donors or acceptors for hydrogenases from phototrophic bacteria.     

Transition metal complexes of amino acids and derivatives containing disulphide bridges

The interaction of cobalt(II), nickel(II), copper(II) and zinc(II) with D-penicillamine disulphide, oxidized glutathione and L-cysteinylglycine disulphide were studied by pH-metric, spectrophotometric and EPR methods. D-Penicillamine disulphide forms binuclear complexes with all the metal ions studied. The formation of 1:1 complexes is characteristic of oxidized glutathione. L-Cysteinylglycine disulphide behaves like dipeptides, but the presence of two separate peptide moieties also results in the formation of various binuclear complexes. Metal ion-disulphide binding was not observed in any case.     

Optical enrichment of dansyl-rac-amino acids by formation of crystalline inclusion complexes with cyclodextrins

Optical enrichment from racemic dansyl-leucine, dansyl-norleucine, and dansyl-phenylalanine with both beta- and gamma-cyclodextrins in water is reported. Initial crystallization yielded the dansyl-L-Leucine isomer complexed in excess with beta-cyclodextrin with an optical purity of 62-78% depending on experimental conditions. The optical purities obtained for L-norleucine and L-phenylalanine were 71 and 64%, respectively. The optical purity can be increased with continued recrystallization. The dansyl-D-leucine isomer was obtained in the mother liquor with an optical purity of 54-93% depending on experimental conditions. The optical purities obtained for D-norleucine and D-phenylalanine were 72 and 58%. The optical purity of the isomer depended on the molar ratio of host:guest and the pH value of the solution. Optimum enrichment of both enantiomers was achieved with host:guest ratios of 2:1 and 3:1. Although maximum crystalline yield of the dansyl-leucine/CD inclusion complex was obtained at a pH of 3.5, optical purity of both enantiomers was less than that obtained at other pHs. The influence of the molar ratio of host:guest and the pH value of the solution are discussed. This method is suitable for large-scale enantiomeric separations.     

Activation of the binuclear metal center through formation of phosphotriesterase-inhibitor complexes

Phosphotriesterase (PTE) from Pseudomonas diminuta is a binuclear metalloenzyme that catalyzes the hydrolysis of organophosphate nerve agents at rates approaching the diffusion-controlled limit. The proposed catalytic mechanism postulates the interaction of the substrate with the metal center and subsequent nucleophilic attack by the bridging hydroxide. X-band EPR spectroscopy was utilized to monitor the active site of Mn/Mn-substituted PTE upon addition of two inhibitors, diisopropyl methyl phosphonate and triethyl phosphate, and the product of hydrolysis, diethyl phosphate. The effects of inhibitor and product binding on the magnetic properties of the metal center and the hydroxyl bridge were evaluated by measuring changes in the features of the EPR spectra. The EPR spectra support the proposal that the binding of substrate analogues to the binuclear metal center diminishes the population of hydroxide-bridged species. These results, in conjunction with previously published kinetic and crystallographic data, suggest that substrate binding via the phosphoryl oxygen at the beta-metal weakens the coordination of the hydroxide bridge to the beta-metal. The weakened coordination to the beta-metal ion increases the nucleophilic character of the hydroxide and is coupled to the increase in the electrophilic character of the substrate.     

Kinetics of metal elimination in oysters from a contaminated estuary

In oysters Crassostrea gigas translocated from a metal-enriched estuary (Gironde, France) to a comparatively clean site, the Bay of Bourgneuf (France), Cd, Cu and Zn concentrations were determined monthly in the whole soft tissues, or in different fractions (cytosolic or insoluble) of gills and digestive glands. In all cases, the concentrations of all of the three metals decreased logarithmically and half-lives were always shortest for Cd (86-251 days). After 4 months, the Cd concentration had become not significantly different from the threshold considered safe for human consumption (1 mg kg(-1) wet wt.). In the digestive gland, half-lives were similar in cytosolic and insoluble fractions. In contrast, in the gills, elimination patterns differed markedly between these fractions. The long half-lives calculated for divalent metals in the insoluble fraction of the gills (1505 and 3010 days for Zn and Cu, respectively) is possibly due to a fossilization of metals in intracellular membrane-bound inclusions as shown previously in Ostrea edulis. It is interesting to underline that elimination is fastest for cytosolic metals compared to the insoluble fraction.     

Species associations and metal contents of algae from rivers polluted by heavy metals

SUMMARY. The algal flora of the Rivers Hayle and Gannel. whieh drain copper and lead mining regions of Cornwall, are described and compared. Although fluctuations in the rarer members of the algal communities were observed, the dominant filamentous algae at most sites did not change over the year of study. Both the total algal abundance and the number of species were depressed at high metal sites. Associations of species that were evident in field samples were confirmed and correlated with water metal levels by principal component analysis. The close similarity between the flora of similar sites on the copper-polluted River Hayle and the lead-polluted River Gannei implies that the degree of metal pollution, rather than the polluting metal per se, determines the species present. All mine sites were characterized by a Microspora -community whereas a Zygnemales community of Spirogyra and Mougeotia species was typical of low metal pollution. Moderately polluted sites downsteam of the mines had an intermediate flora of Zygnemaies, Microsporales. Ulotrichales and gelatinous Volvocales and Tetrasporales species. No species could be said to invariably indicate metal pollution; the most abundant species at highly contaminated sites were also those with the widest distributions. Field samples of filamentous algae (mainly Spirogyra, Zygogonium, Mougeotia and Microspora species) contained metal concentrations several orders of magnitude greater than ambient levels. For copper and iron, both algal metal contents and concentration ratios (μg g-1 algae/μg ml-1 water) were positive functions of water metal levels, although algal iron appeared to plateau at water concentrations of about 1 mg ml-1. Algal lead concentrations, but not the concentration ratios, also were positively correlated with water lead levels. Thus, for these three metals, the algal metal contents were indicative of ambient conditions. In contrast, algal zinc concentrations were nearly constant and consequently the concentration ratios for this metal were inversely related to water levels. This result suggests that unlike the uptake of other metals, uptake of zinc by these aigae may be strictly regulated.     

Stabilization of estradiol-receptor complexes by elimination of cytosolic factors

Treating mature rat uterine cytosol with dextran coated charcoal (DCC) for 2 hrs at 0-4C in the absence of ligand causes the subsequently formed receptor-estradiol complex to be stable at 37C. Receptor binding is increased by the DCC treatment for uteri excised at metestrus or diestrus but remains nearly unchanged for uteri obtained at proestrus or estrus. Results suggest that the DCC removes or inactivates factor(s) present in the cytosol which render the receptor complex thermolabile.     

Action of cysteine hydrochloride in the body on the immune response and the formation of antigen-antibody complexes

The present work demonstrates that the injection of cysteine hydrochloride, a reducing agent, into animals has a pronounced effect on the character of immune response to proteinaceous antigen (bovine serum albumin): the formation of antibodies is enhanced, the synthesis of IgM is prevented from being changed over to the synthesis of IgG, the time of the circulation of free antigen is reduced and the time of their circulation in the blood is increased.     

Imidazolium formation from the reaction of N-heterocyclic carbene stabilised group 13 trihydride complexes with organic acids

The reactions of the N-heterocyclic carbene (NHC) stabilised group 13 trihydride complexes [AlH₃(IMeMe)] (1) (IMeMe = 1,3,4,5-tetramethylimidazol-2-ylidene), [AlH₃(IⁱPrMe)] (2) (IⁱPrMe = 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene) with three molar equivalents of phenol, and [InH₃(IMes)] (3) (IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazole-2-ylidene) with one molar equivalent of 1,1,1,5,5,5-hexafluoropentan-2,4-dione (F₆acacH) are presented. These render the imidazolium tetraphenoxyaluminate species; [IMeMe · H][Al(OPh)₄] (4) and [IⁱPrMe · H][Al(OPh)₄] (5), and 1,3-bis(2,4,6-trimethylphenyl)imidazolium 1,1,1,5,5,5-hexafluoropentan-2,4-dionate; [IMes · H][CH{C(O)CF₃}₂] (6), the latter leading to metallohydride decomposition. The molecular structures of 4 and 6 are described.     

Various properties of DNA from isolated fractions of the mouse synaptonemal complexes

A fraction of synaptonemal complexes (SC) isolated from mouse spermatocytes has been electrophoretically purified in agarose gel. The DNA from the SC fraction constitutes approximately 0.5% of total nuclear DNA, and its molecules have length heterogeneity from 1 k.b. to 20 k.b. The content of beta-globin gene is the same in DNA from the SC fraction and in total nuclear DNA. The specificity of DNA from the SC fraction is manifested by higher contents of the repeated alternative sequences GT/CA and B1-sequence that is probably due to the processes of genetic meiotic recombination.     

Role of biocomponents of the bile and excreta in the elimination of plutonium and americium from the body

A study was made of the role of biocomponents of bile, urine and feces in the elimination of plutonium and americium from the organism. Plutonium 239 and americium 241 were separated in bile due to higher tropism of plutonium to low molecular weight ligands, and of americium, to a protein-containing fraction. The status of plutonium excreted in feces was the same as the physicochemical status of americium. Plutonium 239 and americium 241 eliminated in urine were in a completely ultrafiltered state.