Effect of monovalent cations on the catalytic and spectral properties of tyrosine-phenol-lyase from Citrobacter intermedius

The action of monovalent cations Li+, Na+, K+, Rb+, Cs+, NH4+ on catalytic and physico-chemical properties of bacterial tyrosine--phenol-lyase was investigated. It was shown that K+, Rb+, Cs+, NH4+ were the noncompetitive activators of the enzyme, Na+ was an inhibitor, Li+ did not influence the catalytic activity. The values of KA and Vmax were determined for the activators in the reaction of alpha, beta-elimination of L-tyrosine. Monovalent cations affect the absorption and CD spectra of the enzyme and its complex with the quasi-substrate--L-alanine. It was suggested that an activation of tyrosine phenollyase by monovalent cations was connected with the increase of the active protonated form of the holoenzyme (lambda max 420 mm) induced by the cations-activators.     

Interaction of pepsin with aromatic amino acids and their derivatives immobilized to Sepharose

A new LC-MS/MS method for the separation, identification and quantification of residues of 17alpha-estradiol (17alpha-E2) and 17beta-estradiol (17beta-E2) in bovine serum is reported. Deuterium-labelled 17beta-estradiol was used as internal standard. The method was in-house validated in accordance with European Union criteria and adopted in a proficiency study organised by the Community Reference Laboratory (CRL-RIVM, Bilthoven, The Netherlands). The analytes were extracted from serum using acetate buffer, purified by C18 solid-phase extraction (SPE) and chromatographed on a C18 LC column. They were then ionized in a heated nebulizer (HN) interface operating in negative ion mode, where only intact deprotonated molecules, [M-H](-), were generated at m/z 271 and 274 for 17alpha/17beta-E2 and 17beta-E2-d(3), respectively. The decision limits obtained (CCalpha, i.e., critical concentration alpha) were 0.06 ng/mL and 0.03 ng/mL, respectively for 17alpha-E2 and 17beta-E2. Detection capability (CCbeta, i.e., critical concentration beta) values were 0.08 ng/mL and 0.04 ng/mL, respectively, for 17alpha-E2 and 17beta-E2. Precision, accuracy and specificity were satisfactory, recovery ranged from 86.3% to 93.2% and the method resulted sensitive for the required purposes. This method is currently in use for Official Control purposes.     

Factors, determining the effectiveness of tryptophanase interaction with amino acids

Inhibition of tryptophanase-catalyzed decomposition of S-(o-nitrophenyl)-L-cysteine by a variety of amino acids has been investigated. For amino acids similar to the natural substrate and for those having minimal steric requirements for the side chain, the linear correlation exists between-RTlnKi and side chain hydrophobicity. L-ornithine and L-arginine are anomalously potent inhibitors taking into account low hydrophobicity of their side chains. This can be explained by an interaction between a positively charged group of the side chain of L-arginine or L-ornithine and a nucleophilic group of the active site. The comparison of affinity of tryptophanase for L-phenylalanine and L-homophenylalanine indicates that there is a special locus in the active site where aromatic groups are bound and oriented approximately parallel to the cofactor plane experiencing no steric hindrance. For a large number of amino acids the rates of the enzymic alpha-proton exchange in 2H2O are comparable with the rate of the reaction with L-tryptophan. Very low rate of alpha-proton exchange observed with L-alanine is an exception.     

The effect of 2-oxoglutarate and biotin in the release of amino acids by Citrobacter intermedius C3

Excretion of amino acids by Citrobacter intermedius C3 was assayed in a mineral medium with glucose as carbon source. Glutamic acid is the main amino acid excreted in liquid medium and it is also detected at the colonial level in solid medium. Mutants with different behaviour with respect to the excretion of amino acids are studied. The presence of 2-oxoglutarate in the medium induced excretion in all strains. On the other hand when biotin was added to the culture media amino acid excretion was partially reduced.     

Isolation and properties of tyrosine phenol-lyase from Citrobacter intermedius

A method for preparation of homogeneous tyrosine phenol lyase (EC 4.199.2) from Citrobacter intermedius has been developed. The cells were cultivated in the media with a view to obtain a cell culture with a high activity of tyrosine phenol lyase. The isoelectric point for the enzyme lies at pH 4.9. Tyrosine phenol lyase is strictly stereospecific: it catalyzes the formation of pyruvate only from L-tyrosine, but not from D-tyrosine. Kinetic studies showed that K+ and NH4+ cations are non-competitive activators of the enzyme (Ka = 3.57 X 10(-3) and 1.34 X 10(-4) M, respectively).     

Metabolism of dicarboxylic amino acids and their amides in bacteria of the genus Citrobacter]

In 58 Citrobacter strains the pathways of the utilization of dicarbonic amino acids and their amides were studied. These organisms were found to be incapable of decarboxylating glutaminic and asparaginic acids, as well as their amides. All the strains could actively desamidizate asparagine. Not all of these strains showed glutaminase activity. Aspartate-aminotransferase occurred twice as often as alanine-aminotransferase, the level of activity being approximately the same. The Citrobacter strains desamidizated asparaginic acid with great constancy, but only in 1/3 of them this reaction occurred via an aspartase route. The desamidization of asparaginic acid in Citrobacter seemed to proceed in different ways. The desamidization of glutaminic acid was observed only in a part of the strains, and the reaction proceeded less actively.     

Interaction of aminoacyl-tRNA-synthetases with amino acids

The review deals with interactions of the key enzymes of the protein biosynthesis-aminoacyl-tRNA synthetases (EC 6.1.1.) with amino acids and their analogues, considering the contribution of different groups in the process of specific complex formation and catalysis. The important role of alpha-amino group of amino acid in the enzyme recognition has been revealed. Modification of the carboxylic group does not change significantly the analogues complex formation with aminoacyl-tRNA synthetases. However this group is essential for amino acid rearrangement in the specific complex with the enzyme. The structural organization of the enzyme binding sites specific for amino acids and the enzyme interaction with the analogues of aminoacyladenylates are discussed.     

Utilization of glucose and amino acids byBacteroides intermedius andBacteroides gingivalis

Growth ofBacteroides intermedius was promoted only moderately by glucose, and the incorporation of¹⁴C-glucose into cells was limited. WithBacteroides gingivalis growth promotion was negligible and glucose incorporation even more restricted. Both species grew prolifically on protein hydrolysates containing peptides, but grew poorly on acid-hydrolyzed casein even when supplemented with amino acids. These results are discussed in relation to the ecological distribution of these species compared to saccharolytic bacteroides.     

Interaction of aspartate aminotransferase with amino acids

1. The capacity of various amino acids to convert the pyridoxal form of aspartate aminotransferase into the pyridoxamine form has been investigated. 2. Glutamate has the highest converting capacity; aspartate, α-aminopimelate, α-aminoadipate and other amino acids follow. 3. The converting capacity of the various amino acids assayed is connected with their structural features. 4. A possible role of amino acids as secondary substrates of aspartate aminotransferase is suggested.     

Interaction of auxin with dibasic amino acids.

Auxin interacts with dibasic amino acids forming charge-transfer complexes. The interaction is of hydrophilic character, the strength of interaction increasing with the logarithm of auxin concentration. Sodium, potassium, magnesium and calcium ions decrease the strength of interaction, while their inhibitory effect increases with increasing concentration and ion charge.     

Synthesis of selenocysteine and selenomethionine derivatives from sulfur-containing amino acids

Selenium-containing amino acids have attracted increasing interest from view points of the importance as active centers of several selenoenzymes, the biological synthesis, the metabolism, and the use for structure determination of proteins. In this article, our recent progresses in the transformation from sulfur-containing amino acids to selenocysteine (SeCys) and selenomethionine (SeMet) derivatives are reviewed along with the surveys of general organic methodologies for the synthesis of SeCys and SeMet derivatives in the literature. The S-->Se modification (i.e., the chemical atomic mutation) would be a useful approach to peptide synthesis involving selenoamino acid residues.     

Aromatic amino acids and their derivatives as ligands for the isolation of aspartic proteinases

Affinity chromatography was used to study an interaction of aspartic proteinases with immobilized aromatic amino acids and their derivatives. The following ligands were used: L-tyrosine, 3-iodo-L-tyrosine, 3,5-diiodo-L-tyrosine, L-phenylalanine, p-iodo-L-phenylalanine and N-acetyl-L-phenylalanine. With the exception of the last one, ligands were coupled directly to divinyl sulfone activated Sepharose 4B. For the preparation of immobilized N-acetyl-L-phenylalanine, divinyl sulfone activated Sepharose 4-B with linked ethylene diamine was used. Porcine pepsin was used for the evaluation of the capacity of the prepared affinity carriers. The capacity of the immobilized amino acid derivatives significantly increased in comparison with the non-derivatized amino acids. The prepared immobilized ligands were further used for the separation of human pepsinogens.     

Oxic and anoxic growth of a new Citrobacter species on amino acids

A facultatively anaerobic bacterium, strain P-88, was enriched selectively under dual limitation by glutamate and oxygen in a chemostat. The new strain is a gram-negative motile rod. The mol% guanine plus cytosine of the DNA is 51.4±0.6 mol%. The organism grows on citrate as a sole source of carbon and energy, does not form acetoin, does not induce lysine decarboxylase and was thus classified as a species of the genus Citrobacter. A remarkable characteristic of the new isolate is its ability to grow on several amino acids with either a respiratory or a fermentative type of metabolism. Under strictly anoxic conditions glutamate was fermented to acetate, H₂, CO₂ and ammonia. Asparagine, aspartate and serine could also be fermented. Furthermore, all type strains of the genus Citrobacter were shown to have the same fermentative abilities. Based on enzyme activities determined in cell-free extracts a combination of the methylaspartate pathway and the mixed acid fermentation of Enterobacteriaceae is proposed to explain the glutamate fermentation pattern observed in cultures of strain P-88. Analysis of the growth of strain P-88 in continuous culture with various degrees of oxygen supply, demonstrated that the bacterium can rapidly switch between oxic and anoxic metabolism. Cultures of strain P-88 grown under oxygen limitation simultaneously respire and ferment glutamate, suggesting that the organism is particularly well adapted to growth in microoxic environments.     

Interaction of metal ions with nucleic acids. Interaction of copper(II) with pyrimidine nucleosides and their derivatives.

1. In aqueous and non-aqueous solutions, copper(II) interacts with the N-3 of cytidine but not with the carbonyl group oxygens of pyrimidine nucleosides. 2. In aqueous solution, copper(II) interacts with the phosphate group and ribose of pyrimidine nucleotides, and additionally with N-3 of 5'-CMP. 3. Broadening of resonance signals of the H-5 proton of 5'-UMP and C-5 of 5'-UMP and 5'-TMP results probably from the interaction between metal ion and the phosphate group situated in direct vicinity of the above atoms. 4. In the copper(II)-pyrimidine nucleotide complexes in solid state, copper is coordinated with the phosphate group, and in 5'-CMP additionally with the pyrimidine moiety of the nucleotide.     

Analysis of methylthiohydantoins of amino acids by gas-liquid chromatography of their trimethylsilyl derivatives

A procedure is described for the analysis of methylthiohydantoins of amino acids from the Edman degradation of proteins and peptides by gas-liquid chromatography of their trimethylsilyl derivatives. The procedure is applicable to the methylthiohydantoins of all the amino acids commonly found in proteins with the exception of arginine, which did not yield a volatile derivative, and hydroxyproline and hydroxylysine, which were not investigated. Chromatographic separation is achieved in a single run with only one unresolved pair, which can be separated by a supplementary procedure requiring only 4.5 min.     

Interaction of amino acids with glycyl-glycine transport in the mammalian intestine

In order to investigate a possible interaction between free amino acids and dipeptides during their mucosal uptake in man and monkey, perfusion studiesin vivo and uptake studiesin vitro using labelled and non-labelled dipeptides and amino acids have been carried out. In contrast to the observations of other workers, inhibition of glycyl-glycine uptake was observed with free leucine and methioninc but not with glycine, proline, hydroxyproline or alanine. Leucine and methionine caused inhibition of cytosol glycyl-glycine hydrolase activity, while glycine had no effect. The dipeptide uptake and dipeptide hydrolysis by cytosol enzyme was competitively inhibited by leucine. Although brush border glycyl-glycine hydrolase was also inhibited by leucine, the inhibition was noncompetitive. These data indicate that a few free amino acids can interact with dipeptides during uptake. This interaction might occur either at the transport step or at the stage of intracellular dipeptide hydrolysis. The work reported here was carried out at Wellcome Research Unit, Christian Medical College and Hospital, Vellore 632 004.