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PubMed1984

Characterization of L-glutamic acid transport by glioma cells in culture: evidence for sodium-independent, chloride-dependent high affinity influx.

The transport of radiolabeled L-glutamic acid by LRM55 glioma cells in culture was examined. Time course studies indicated that L-[3H]glutamic acid is rapidly accumulated, and then 3H is lost from the cell, presumably in the form of glutamate metabolites. Kinetic analysis of L-glutamate uptake provided evidence for two components of transport. A low affinity component was found to persist at 0 to 4 degrees C and was not saturable, influx being proportional to the substrate concentration. A high affinity component, resolved by subtraction of the influx at 0 to 4 degrees C, followed Michaelis-Menten kinetics having a Km of 123 microM and a Vmax of 2.99 nmol/min/mg of protein. The transport system was highly substrate-specific: At least 27-fold larger concentrations of the most potent analogues--cysteic acid, cysteine sulfinic acid, and L-aspartic acid--were required to compete effectively with glutamate. Second, the system was not severely affected by exposure to inhibitors of oxidative phosphorylation or gamma-glutamyltranspeptidase. Third, only 65% of the high affinity uptake was dependent upon the presence of sodium, the other 35% being dependent upon chloride. These observations were supported by the findings that uptake was only partially inhibited by ouabain and quite effectively reduced by several inhibitors of chloride transport. The results of this study provide information on the properties of low affinity glutamate transport, as well as the first description of sodium-independent, chloride-dependent high affinity glial transport. The high affinity component of influx is stimulated by elevated potassium and inhibited by several pharmacological agents. The sodium independence of a significant proportion of high affinity glutamate transport suggests that glutamate binding studies done in sodium-free medium with intact cells may be confounded by a considerable amount of intracellular uptake.

Animals↗
PubMed1975

Kinetic analysis of the mechanism of insulin degradation by glutathione-insulin transhydrogenase (thiol: protein-disulfide oxidoreductase).

Kinetic studies have been made with glutathione-insulin transhydrogenase, an enzyme which degrades insulin by promoting cleavage of its disulfide bonds via sulfhydryl-disulfide interchange. The degradation of 125I-labeled insulin by enzyme purified from beef pancreas was studied with various thiol-containing compounds as cosubstrates. The apparent Km for insulin was found to be a function of the type and concentration of thiol; values obtained were in the range from 1 to 40 muM. Lineweaver-Burk plots for insulin as varied substrate were linear, whereas those for the thiol substrates were nonlinears: the plots for low molecular weight monothiols (GSH and mercaptoethanol) were parabolic; those for low molecular weight dithiols (dithiothreitol, dihydrolipoic acid, and 2,3-dimercaptopropanol) were apparently linear modified by substrate inhibition; and the plots for protein polythiols (reduced insulin A and B chains and reduced ribonuclease) were parabolic with superposed substrate inhibition. The nonparallel nature of the reciprocal plots for all substrates shows that the enzyme does not follow a ping-pong mechanism. Product inhibition studies were performed with GSH as thiol substrate. Oxidized glutathione was found to be a linear competitive inhibitor vs. both GSH and insulin. The S-sulfonated derivative of insulin A chain was also linearly competitive vs. both substrates. Inhibition by S-sulfonated B chain was competitive vs. insulin; the data eliminated the possibility that this derivative was uncompetitive vs. GSH. Experiments with the cysteic acid derivatives of insulin A and B chains similarly excluded the possibility that these were uncompetitive vs. either substrate. These inhibition studies indicate that the enzyme probably follows a randdom mechanism.

Animals↗
PubMed2006

Comparative species utilization and toxicity of sulfur amino acids.

Animal studies have shown that several methionine (Met) and cysteine (Cys) analogs or precursors have L-Met- and L-Cys-sparing activity. Relative oral bioavailability (RBV) values, with the L-isomer of Met and Cys set at 100% (isosulfurous basis), are near 100% for D-Met for animals but only about 30% for humans. Both the OH and keto analogs of Met have high RBV-sparing values, as does N-acetyl-L-Met (the D-isomer of acetylated Met has no bioactivity). L-Homocysteine has an RBV value of about 65% for Met sparing in rats and chicks, but D-homocysteine has little if any Met-sparing activity. S-Methyl-L-Met can partially spare Met, but only when fed under dietary conditions of choline/betaine deficiency. Relative to L-Cys, high RBV values exist for L-cystine, N-acetyl-L-Cys, L-homocysteine, L-Met, and glutathione, but D-cystine, the keto analog of Cys, L-cysteic acid, and taurine have no Cys-sparing activity. l-2-Oxothiazolidine-4-carboxylate has an RBV value of 75%, D-homocysteine 70%, and DL-lanthionine 35% as Cys precursors. Under dietary conditions of Cys deficiency and very low inorganic sulfate (SO4) ingestion, dietary SO4 supplementation has been shown to reduce the Cys requirement of several animal species as well as humans. Excessive ingestion of Met, Cys, or cystine has also been studied extensively in experimental animals, and these sulfur amino acids (SAA) are well established as being among the most toxic of all amino acids that have been studied. Even though Cys and its oxidized product (cystine) are equally efficacious at levels at or below their dietary requirements for maximal growth, Cys is far more toxic than cystine when administered orally in the pharmacologic dosing range. Isosulfurous (excess) levels of cystine, N-acetyl-L-Cys, or glutathione are far less growth depressing than L-Cys when 6 to 10 times the minimally required level of these SAA compounds are fed to chicks.

Alanine↗
PubMed1984

The utilization and safety of isomeric sulfur-containing amino acids in mice.

Growth assays on a synthetic amino acid diet fed to mice showed that substituting D-methionine for the L-isomer resulted in a dose-dependent relative weight gain reaching approximately 76% when D-methionine was fed at a level equivalent to that optimal for the L-form. L-Cysteine and L-cystine stimulated growth in the presence of suboptimal levels of L-methionine, but D-cystine was growth depressing. L-Cystine is at least equally efficient in stimulating growth in the presence of D-methionine as in the presence of the L-isomer. Compared to a suboptimal (25% of maximum) level of L-methionine alone, supplements to this level L-methionine by N-acetyl-L-cysteine produced a weight gain of 214%; L-cysteine, 178%; L-cysteic acid, 154%; DL- + meso-lanthionine, 127%; L-cysteine sulfinic acid, 113%; D-cysteine, 76%; and S-methyl-L-cysteine, 13%. The observed growth-depressing effect of D-cysteine, D-cystine and S-methyl-L-cysteine at a concentration no greater than that optimal for methionine implies that these three sulfur-containing amino acids may be toxic. The results are discussed in terms of known and postulated transamination and transsulfuration pathways that govern the biological utilization of isomeric sulfur-containing amino acids and derivatives.

Amino Acids, Sulfur↗
PubMed2000

New carrier electrolytes for the separation of chlorophenols by capillary electrophoresis.

Optimum conditions for the separation of positional isomers of chlorophenols by capillary zone electrophoresis (CZE) were established. The behavior of five volatile electrolytes (L-cysteic acid, 3-amino-1-propanesulfonic acid, aminomethanesulfonic acid, diethylmalonic acid, and ammonium acetate) was compared. The best performance based on low electrophoretic current and high separation efficiency was obtained for diethylmalonic acid as working electrolyte. The influence of pH on the separation, using both uncoated fused-silica capillaries and modified capillaries (NaAMPS from EKT) with anionic coating, was discussed. Moreover, the effect of electrolyte concentration and applied voltage using fused-silica capillaries was studied. The optimum CZE conditions that allowed the separation of 16 chlorophenols were 20 kV, 30 mM diethylmaIonic acid, pH 7.25, and uncoated fused-silica capillary. Figures of merit such as run-to-run and day-to-day precision, linearity, and limits of detection were calculated.

Chlorophenols↗
PubMed2006

Analysis of structural changes in bleached keratin fibers (black and white human hair) using Raman spectroscopy.

To investigate the influence of bleaching treatments on keratin fibers, the structure of cross-sections at various depths of bleached human hair (black and white human hair) was directly analyzed without isolating the cuticle and cortex, using Raman spectroscopy. The S-S band intensity existing from the cuticle region to the center of cortex region of virgin white human hair decreased, while the S-O band intensity at 1040 cm(-1), assigned to cysteic acid, increased by performing the bleaching treatment. Especially, the S-O band intensity of the cuticle region increased remarkably compared with that of the cortex region. Also, the amide III (unordered) band intensity in the cortex region increased, indicating that some of the proteins existing throughout the cortex region changed to the random coil form. Moreover, it has been found that the S-S band intensity existing from the cuticle region to the center of the cortex region of the virgin black human hair decreased remarkably, while the S-O band intensity increased significantly compared with that of the virgin white human hair by performing the bleaching treatment. From these experiments, we concluded that the melanin granules including metal ions act as a decomposition accelerator for the oxidizing agent, thereby leading to a higher level of disulfide (-SS-) group cleavage in the black human hair compared with that of the white human hair.

Animals↗
PubMed1994

Transport of L-arginine in cultured glial cells.

Uptake of radiolabelled L-arginine was studied in four different kinds of glial cultures, in astroglia-rich primary cultures derived from neonatal rat and mouse brains, in pure murine astrocyte cultures, and in rat glioma cells C6-BU-1. A saturable component of uptake was found in all cases with KM values between 15 and 35 microM and Vmax values between 0.8 and 2.5 nmol.min-1.(mg protein)-1. In addition, in all cell types a non-saturable component dominated total uptake at high concentrations of extracellular arginine. Rates of uptake of arginine were not affected when Na+ or Cl- were absent from the incubation buffer. Carrier-mediated uptake of arginine was reduced by depolarizing concentrations of K+ and strongly inhibited by an excess of lysine or ornithine. Histidine, asparagine, glutamine, citrulline, creatine, NG-nitro-L-arginine, NG-monomethyl-L-arginine, or L-canavanine inhibited L-arginine transport to various degrees. Uptake of arginine was not reduced in the presence of serine or alanine cysteic acid, N-methyl-alpha-aminoisobutyric acid, or 2-aminobicyclo-(2.2.1)-heptane-2-carboxylic acid. Rates of uptake of arginine were increased when cells had been preloaded with lysine. Preincubation of primary cultures, but not glioma cells, with bacterial lipopolysaccharide stimulated transport of arginine by increasing the Vmax value of uptake. This stimulation was dependent on protein synthesis. The results suggest that, at physiological concentrations, arginine is taken up into the glial cells with the help of the transport system "y+" for basic amino acids. In glial primary cultures, uptake of arginine appears to be regulated by compounds which also exert influence on nitric oxide synthesis.

Amino Acids↗
PubMed2003

The effect of oxidation or alkylation on the separation of wool keratin proteins by two-dimensional gel electrophoresis.

Comparative two-dimensional electrophoretic (2-DE) studies were performed over a time-course to examine the effect of oxidation or alkylation on the separation of wool keratin proteins. The effect of oxidation was followed by treating scoured wool fibres with increasing levels of hydrogen peroxide, ranging from 0-12 g/L, using conditions mimicking the industrial wool bleaching process. Peroxide treatment was found to have only a minor effect on the 2-DE separation of the intermediate filament protein (IFP) class. Conversely, peroxide treatment of the 24-28 kDa high sulphur protein (HSP) class, which contains up to 40 cysteine residues per protein, resulted in the gradual disappearance of the major HSP spots correlated with the appearance of a few discrete spots at lower isoelectric point (pI). This suggested that only a few specific cysteine residues were being oxidized to cysteic acid by treatment with hydrogen peroxide. Peroxide treatment also appeared to have affected a discrete number of cysteine residues among proteins in the high glycine-tyrosine protein (HGTP) class, reducing the intensity of the high pI spots, while correspondingly increasing the intensity of those at lower pI. In a separate study, wool proteins were alkylated with iodoacetamide (1 M, pH 8) for periods ranging from 10 min to 48 h. In contrast to treatment with peroxide, the pI values of the HSP spots were unaffected by alkylation, irrespective of the length of this treatment. Alkylation resulted in a shift to lower pI and a loss of resolution of individual spots in the Type I and II IFP trains, to the extent that after 24 h alkylation individual spots in these trains merged. In addition after 1 h the intensity of the high pI Type II IFPs decreased until they were no longer visible on the 2-DE map after 24 h. Similarly as alkylation time increased, the major, high pI HGTP spots decreased in intensity. In unison with their decrease, some of the lower pI spots increased in intensity, while new spots appeared at more acidic pIs. Mass spectral studies indicated that cysteine alkylation was relatively fast, with 70-95% of the cysteines in the keratin proteins being alkylated within the first 10 min, while in the case of the HGTPs there was evidence for noncysteine alkylation occurring within this period. Alkylation of proteins for periods of up to 6 h prior to electrofocusing is being promoted as a better alternative to the current 2-DE protocol of the inclusion of a reductant in the immobilized pH gradient rehydration solution. This study has clearly demonstrated that long alkylation times do not suit all protein types or classes.

Alkylating Agents↗
PubMed1991

The cysteine transport system of Saccharomyces cerevisiae.

Although Saccharomyces cerevisiae strains had different cysteine uptake activities, they revealed monophasic uptake kinetics and had the same KT (83.3 microM). The optimal pH of cysteine uptake was between 4.5 and 5.0, but the activity was quickly lost if cells were kept in buffer. When the activity was measured in the growth medium, it increased in the presence of EDTA and greatly decreased in the presence of mercuric chloride. Thioglycol as well as metabolic inhibitors such as dinitrophenol and azide were inhibitory. Homocysteine and methionine were competitive and non-competitive inhibitors, respectively. Cysteamine and cysteic acid were not inhibitory. From these observations, we conclude that the system mediating uptake of cysteine is specific (we thus name it the cysteine transport system) and that the cysteine transport system recognizes not only the SH-group but also amino- and carboxyl-groups. In wild-type strains the cysteine transport system was derepressed only when the cells were incubated without any sulfur source. On the other hand, in cysteine-dependent mutants, cysteine uptake activity increased with increase of exogenous supply of cysteine, glutathione or methionine. From this result, we suspect that the cellular cysteine level is the limiting factor for biosynthesis of the cysteine transport system in cysteine-dependent strains.

Biological Transport↗
PubMed1983

Molecular specificity of the tubular resorption of "acidic" amino acids. A continuous microperfusion study in rat kidney in vivo.

Single sections of superficial proximal convolutions of rat kidney were microperfused in vivo and in situ. The perfusion fluids contained radioactively labelled L- or D-aspartate, L-glutamate, L-pyroglutamate, or N-methyl-D-aspartate. L-gamma-Carboxyglutamate as well as the other amino acids were added in the unlabelled form. Results. L- and D-Aspartate (0.073 mmol X 1(-1)) are quickly resorbed at about the same rate. D-Aspartate resorption was blocked by L-aspartate (5 mmol X 1(-1)) but not by beta-alanine (5 mmol X 1(-1)). L-Aspartate resorption was inhibited by L-glutamate (2 mmol X 1(-1)) but not by D-glutamate, L-asparagine, L-phenylalanine or by succinate (2 mmol X 1(-1), each). The fast resorption of L-glutamate (0.073 mmol X 1(-1)) was blocked by D-aspartate, L-cysteate (2 mmol X 1(-1)), but not by 3-mercaptopicolinic acid (0.15 mmol X 1(-1)), L-glutamine, 2-oxoglutarate, taurine, N-methyl-L-glutamate or kainic acid (2 mmol X 1(-1), each). L-gamma-Carboxyglutamate (0.66 mmol X 1(-1)) and N-methyl-D-aspartate (2 mumol X 1(-1)) were found to be resorbed only at an extremely small rate. L-Pyroglutamate (0.076 mmol X 1(-1)) resorption was not influenced by L-glutamate (1 mmol X 1(-1)). Fractional excretion of gamma-carboxyglutamate was 7-25% (L-form) or 45-70% (D-form) at an artificially elevated plasma level of 12 mumol X 1(-1). It is concluded that L- and D-aspartate, L-glutamate, L-cysteate and, to a much smaller extent, L-gamma-carboxyglutamate, are accepted by the tubular resorption mechanism highly specific for "acidic" amino acids. N-Substitution, the amidation of the beta- or gamma-carboxyl group, or the removal of the alpha-amino moiety almost completely abolish the ability of such compounds to be resorbed via this carrier; N-methylated or gamma-carboxylated derivatives of "acidic" amino acids are not resorbed at all from the proximal tubule. The resorption of glutamate, but not of aspartate, is highly stereospecific.

1-Carboxyglutamic Acid↗
PubMed1980

Synthesis of taurine in rat liver and brain in vivo.

The in vivo formation of taurine and the analysis of labeled taurine precursors was examined in rat brain and liver at different times after an intracisternal injection of [35S]cysteine and an intraperitoneal injection of [3H]cysteine, simultaneously administered. The distribution pattern of radioactivity was similar in liver and brain. Most of the labeling in both organs (85% in brain and 80% in liver) was recovered in glutathione (oxidized and reduced), cysteic acid, cysteine sulfinic acid, hypotaurine, cystathionine, and a mixed disulfide of cysteine and glutathione. The relative rates of labeling of cysteine sulfinic acid and taurine in liver and brain suggest than in vivo, liver possesses a higher capacity for taurine synthesis than brain. A small amount of [3H]taurine was detected in brain after intra peritoneal injection of [3H]cysteine. The time of appearance of this [3H]taurine as well as the fact that it occurs when [3H]cysteine is not detectable in brain or plasma suggests that it was probably not synthesized in brain from labeled precursors but formed elsewhere and transported into the brain through an exchange process.

Animals↗
PubMed1982

Stimulated release of 3H-glycine from retina.

The release of 3H-glycine was studied from rabbit retinas. Kainic acid (10(-5) M), a glutamate agonist, evoked prompt CA2+-dependent increased release of 3H-glycine. However, nuciferine (10(-4) M) could not suppress the effect of kainic acid. The effect of glutamic acid (10(-5) M) was significantly reduced in the presence of nuciferine (10(-4) M). The GABA analogues, muscimol and THIP, had no effect on the release of 3H-glycine. Aspartate and cystic acid were also without effect.

Animals↗
PubMed1984

Thin-layer chromatography of thiosulfonate anions.

Organic thiosulfonates of the form RS(O2)S- can be separated from the characteristic contaminants in synthetic preparations by thin-layer chromatography on silica gel. Thiosulfonates and sulfinates can both be visualized, and differentiated, by treatment of plates with a FeCl3 reagent in acetone. Data are presented for seven aromatic and six aliphatic thiosulfonate anions and the corresponding sulfonates and sulfinates. With exception of the series related to cysteic acid, Rf values are always in the order RS(O)2S- greater than RSO3- greater than RSO2-.

Anions↗
PubMed1984

The reaction of ozone with glyceraldehyde-3-phosphate dehydrogenase.

Inactivation of glyceraldehyde-3-phosphate dehydrogenase (GPDH) by ozone can be correlated with oxidation of the active-site -SH residue. Oxidation of peripheral -SH groups, and tryptophan, methionine, and histidine residues occurs concomitantly, but loss of activity depends solely on active-site oxidation. Inactivation is only slightly reversible by dithiothreitol. Kinetic studies show that inhibition of GPDH by ozone mimics noncompetitive inhibition and is characterized as irreversible enzyme inactivation. Analysis of products resulting from ozone oxidation of glutathione suggests that cysteic acid is the product of protein-SH oxidation. Despite oxidation of the active-site -SH , no significant decrease in the Racker band absorbance occurs. This is explained by the appearance of a new chromophore in this region of the absorbance spectrum. Increased absorbance at 322 nm following ozone treatment indicates that tryptophan is converted quantitatively to N-formylkynurenine. When the active-site -SH is reversibly blocked by tetrathionate, enzyme activity is completely recoverable following reaction of the derivatized enzyme with a 1.3X excess of ozone over enzyme monomer. Activity is fully recovered despite the oxidation of peripheral -SH, tryptophan, and histidine residues. Circular dichroism spectra of ozone-treated enzyme show that reaction of GPDH with up to a threefold excess of ozone over enzyme monomer results in no significant disruption of protein secondary structure. Spectra in the near-uv show distinct changes that reflect tryptophan oxidation.

Amino Acids↗
PubMed1985

Biosynthesis of a sulfonolipid in gliding bacteria.

Gliding bacteria of the genus Cytophaga synthesize sulfonolipids (1,2) that contain capnine (1-deoxy-15-methylhexadecasphinganine-1-sulfonic acid). Studies of the incorporation of radiolabeled compounds by C. johnsonae show that cysteate is utilized preferentially to both cystine and inorganic sulfate as a precursor of capnine sulfur and to both cystine and serine as a precursor of carbons 1 and 2 of capnine. The results are consistent with a pathway in which capnine is formed by condensation of cysteate with a fatty acyl CoA. Cystine, added as the sole sulfur source in the presence of glucose, provides the sulfur but not the carbon for capnine. Hence, these cells form cysteate not by direct oxidation of cystine (or cysteine), but by transfer of its sulfur to a different carbon compound.

Alkanesulfonates↗
PubMed1989

Specificity of endoproteinase Asp-N (Pseudomonas fragi): cleavage at glutamyl residues in two proteins.

Endoproteinase Asp-N, a metalloprotease from a mutant strain of Pseudomonas fragi, has been reported to specifically cleave on the N-terminal side of aspartyl and cysteic acid residues. We utilized this enzyme to generate fragments for determining the amino acid sequence of the D-aspartyl/L-isoaspartyl methyltransferase isozyme I from human erythrocytes. Surprisingly, we identified cleavage sites for this enzyme at the N-terminal side of several glutamyl residues in addition to the expected cleavage sites at aspartyl residues. The ability of this enzyme to cleave polypeptides at both glutamyl and aspartyl residues was confirmed by mapping additional sites on erythrocyte carbonic anhydrase I. These results indicate that a more appropriate name for this enzyme may be Endoproteinase Asp/Glu-N.

Amino Acid Sequence↗
PubMed1985

Effects of dithiothreitol, dithioerythritol and chelating agents on 5'-nucleotidase from bull seminal plasma.

5'-Nucleotidase from bull seminal plasma is inhibited by dithiothreitol and dithioerythritol. These reactives proved to dissociate the dimeric glycoprotein 5'-nucleotidase of Mr 160 000 into two subunits of apparent Mr 80 000, indicating that the subunits are held together by interchain disulfide bridges. HPLC determinations of cysteic acid and carboxymethylcysteine protein derivatives resulted in 50 +/- 3 half-cystine plus cysteine residues, while 1.9 +/- 0.4 free cysteine residues were estimated by HPLC analysis. The enzyme is inhibited by EDTA and EGTA, and the inhibition appears to be of the non-competitive type for both the chelating agents. Experiments for the enzyme activity recovery by MgCl2 and CaCl2 additions, after the EDTA and EGTA treatments in the presence of 8 M urea, are reported.

5'-Nucleotidase↗
PubMed1990

The sulfhydryl content of L-threonine dehydrogenase from Escherichia coli K-12: relation to catalytic activity and Mn2+ activation.

When oxidized to cysteic acid by performic acid or converted to carboxymethylcysteine by alkylation of the reduced enzyme with iodoacetate, a total of six half-cystine residues/subunit are found in L-threonine dehydrogenase (L-threonine: NAD+ oxidoreductase, EC 1.1.1.103; L-threonine + NAD(+)----2-amino-3-oxobutyrate + NADH) from Escherichia coli K-12. Of this total, two exist in disulfide linkage, whereas four are titratable under denaturing conditions by dithiodipyridine, 5,5'-dithiobis(2-nitrobenzoic acid), or p-mercuribenzoate. The kinetics of enzyme inactivation and of modification by the latter two reagents indicate that threonine dehydrogenase has no free thiols that selectively react with bulky compounds. While incubation of the enzyme with a large excess of iodoacetamide causes less than 10% loss of activity, the native dehydrogenase is uniquely reactive with and completely inactivated by iodoacetate. The rate of carboxymethylation by iodoacetate of one -SH group/subunit is identical with the rate of inactivation and the carboxymethylated enzyme is no longer able to bind Mn2+. NADH (0.5 mM) provides 40% protection against this inactivation; 60 to 70% protection is seen in the presence of saturating levels of NADH plus L-threonine. Such results coupled with an analysis of the kinetics of inactivation caused by iodoacetate are interpreted as indicating the inhibitor first forms a reversible complex with a positively charged moiety in or near the microenvironment of a reactive -SH group in the enzyme before irreversible alkylation occurs. Specific alkylation of one -SH group/enzyme subunit apparently causes protein conformational changes that entail a loss of catalytic activity and the ability to bind Mn2+.

Alcohol Oxidoreductases↗