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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↗
PubMed1975

Purification and properties of streptococcal nicotinamide adenine dinucleotide glycohydrolase.

Highly purified streptococcal nicotinamide adenine dinucleotide glycohydrolase (NADase) was obtained by utilizing disodium tetrathionate to protect the enzyme by blocking the sulfhydryl groups of streptococcal proteinase. This was followed by two-step ion-exchange chromatography. The pure enzyme, demonstrated as a single band on sodium dodecyl sulfate/polyacrylamide gel electrophoresis, had a specific activity of 11,200 NADase units per mg of protein and was devoid of hemolytic activity. NADase had a molecular weight of about 55,000 as determined by gel filtration, by summation of amino acid residues, and by sodium dodecyl sulfate/gel electrophoresis. The purified enzyme had optimal activity at pH 7.3 and at 40 C and a calculated Km of 5.1 times 10- minus 4 mM. It was inhibited by alpha-iodoacetamide.

Amino Acids↗
PubMed2004

Coupling of the pathway of sulphur oxidation to dioxygen reduction: characterization of a novel membrane-bound thiosulphate:quinone oxidoreductase.

Thiosulphate is one of the products of the initial step of the elemental sulphur oxidation pathway in the thermoacidophilic archaeon Acidianus ambivalens. A novel thiosulphate:quinone oxidoreductase (TQO) activity was found in the membrane extracts of aerobically grown cells of this organism. The enzyme was purified 21-fold from the solubilized membrane fraction. The TQO oxidized thiosulphate with tetrathionate as product and ferricyanide or decyl ubiquinone (DQ) as electron acceptors. The maximum specific activity with ferricyanide was 73.4 U (mg protein)(-1) at 92 degrees C and pH 6, with DQ it was 397 mU (mg protein)(-1) at 80 degrees C. The Km values were 2.6 mM for thiosulphate (k(cat) = 167 s(-1)), 3.4 mM for ferricyanide and 5.87 micro M for DQ. The enzymic activity was inhibited by sulphite (Ki = 5 micro M), metabisulphite, dithionite and TritonX-100, but not by sulphate or tetrathionate. A mixture of caldariella quinone, sulfolobus quinone and menaquinone was non-covalently bound to the protein. No other cofactors were detected. Oxygen consumption was measured in membrane fractions upon thiosulphate addition, thus linking thiosulphate oxidation to dioxygen reduction, in what constitutes a novel activity among Archaea. The holoenzyme was composed of two subunits of apparent molecular masses of 28 and 16 kDa. The larger subunit appeared to be glycosylated and was identical to DoxA, and the smaller was identical to DoxD. Both subunits had been described previously as a part of the terminal quinol:oxygen oxidoreductase complex (cytochrome aa3).

Acidianus↗
PubMedDate not supplied

A new form of inactive renin in rat brain. A latent renin.

A new inactive (latent) form of renin was found in rat brain extract. It is activated by sulfhydryl compounds such as dithiothreitol but not by proteases such as trypsin. The activated form of latent renin in crude brain extract was again inactivated by the disulfide compound sodium tetrathionate. Latent renin was separated, at least partially, from active renin by affinity chromatography on Affi-Gel Blue. In contrast to a marked (10-fold) increase of latent renin by dithiothreitol, the enzyme activity of active renin was increased by less than 50% by this sulfhydryl compound. Thus, the major part of the activating effect of dithiothreitol does not seem to be due to its effect on renin substrate. Latent renin showed affinity for pepstatin-Sepharose gel. These properties indicate that latent renin is different from inactive renin of the zymogen type, which is activated by protease or acid treatment but not by sulfhydryl compounds and does not show affinity to pepstatin. Latent renin has a molecular weight of 45,000 and is reduced to 34,000 upon activation by dithiothreitol. This observation suggests that latent renin may be a renin-inhibitor complex.

Animals↗
PubMed1983

Studies with human erythrocyte pyruvate kinase (PK): effects of modification of sulfhydryl groups.

Cysteinyl residues of red cell pyruvate kinase (PK; ATP: pyruvate phosphotransferase, EC 2.7.1.40) were modified with methylmethanethiosulfonate (MMTS), p-nitrophenoxycarbonyl methyl disulfide (NPCMD), and sodium tetrathionate (NaTT). At pH greater than 7 . 0, K0.5 s phosphoenol-pyruvate (PEP) was markedly increased. Fructose-1,6-diphosphate (FDP) increased affinity for PEP, but K0.5 s (PEP) remained elevated and hyperbolic kinetics were not achieved. Inhibition by negative effectors ATP and alanine was not reversed by PEP and FDP concentrations far greater than those abolishing inhibition of unmodified enzyme. At pH less than 7 . 0, PEP affinity was reduced, and FDP markedly increased Vmax and diminished K0.5 s (PEP). MMTS greatly impaired the thermostability of PK. Acid pH alone and the simultaneous presence of Mg++, K+ and PEP prior to MMTS treatment protected against the effects on PEP kinetics, but did not alter the induction of thermolability. No MMTS effect on the FDP binding site, on ADP kinetics or on the relative effectiveness of GDP, UDP or CDP cofactors was demonstrated. The MMTS-induced alterations closely resembled those observed with certain PK mutants associated with haemolytic anaemia.

Adenosine Diphosphate↗
PubMed1984

A subset of non-histone nuclear proteins reversibly stabilized by the sulfhydryl cross-linking reagent tetrathionate. Polypeptides of the internal nuclear matrix.

When rat liver nuclei are isolated in the presence of the irreversible sulfhydryl-blocking reagent iodoacetamide, digested with DNase I and RNase A, and extracted with 1.6 M NaCl, nuclear envelope (NE) spheres depleted of intranuclear material, as analysed by thin-section electron microscopy, are obtained. Two-dimensional isoelectric focusing (IEF)/SDS-PAGE and non-equilibrium pH gradient electrophoresis (NEPHGE)/SDS-PAGE reveal that the predominant polypeptides are lamins A, B and C. Nuclei isolated in the absence of sulfhydryl blocking reagents yield salt- and nuclease-resistant structures which contain sparse but demonstrable intranuclear material. A number of non-histone polypeptides are seen in addition to the lamins. Nuclei treated with the sulfhydryl cross-linking reagent sodium tetrathionate (NaTT) yield, after exposure to nucleases and 1.6 M NaCl, nuclear matrix-like structures containing an extensive intranuclear network and components of the nucleolus in addition to the NE. Increased amounts of the non-lamin, non-histone polypeptides are recovered with these structures. Subsequent treatment of these NaTT-cross-linked structures with reducing agents in 1.0 M NaCl selectively solubilizes the intranuclear components but leaves the nuclear envelope apparently intact. The lamins remain sedimentable and are virtually absent from the soluble (intranuclear) material. Instead, the major solubilized polypeptides are (a) 68 and 63 kD polypeptides which migrate in the vicinity of lamins B and C, respectively, but are distinguishable from the lamins by immunoblotting and by uni-dimensional peptide mapping; (b) a series of basic 60-70 kD polypeptides (pI greater than 8.0) which are not recognized by anti-lamin antisera; (c) an acidic (pI 5.3) 38 kD polypeptide; and (d) a number of high molecular mass (greater than 100 kD) polypeptides. These observations not only suggest a convenient method for fractionating matrix structures from rat liver nuclei into biochemically and morphologically discrete components, but also identify a subset of major non-lamin, non-histone nuclear polypeptides (comprising approx. 20% of the total nuclear protein) whose intermolecular interactions can be reversibly stabilized apparently by intermolecular disulfide bond formation by NaTT.

Animals↗
PubMed1991

Involvement of tryptophan residue(s) in the specific binding of agonists/antagonists to 5-HT3 receptors in NG108-15 clonal cells.

Chemical modification of the 5-HT3 receptors in membranes from NG108-15 hybridoma cells was achieved using protein modifying reagents specific for various amino acid residues: N-bromosuccinimide for tryptophan, dithiothreitol for cystine, sodium tetrathionate for cysteine, 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide and N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline for aspartic and glutamic acids, diethylpyrocarbonate for histidine, tetranitromethane for tyrosine and 2,3-butanedione for arginine. Among all the reagents tested, N-bromosuccinimide produced the largest alteration in the specific binding of [3H]zacopride onto 5-HT3 receptors. A significant reduction in Bmax (approximately 50%) with no change in Kd were noted on [3H]zacopride specific binding to membranes which were incubated with 40 microM N-bromosuccinimide for 60 min at 25 degrees. The occupancy of 5-HT3 receptor binding sites by various 5-HT3 agonists and antagonists (phenylbiguanide, ondansetron, granisetron, MDL 72222) prevented, at least partially, any subsequent reduction in [3H]zacopride specific binding by N-bromosuccinimide treatment. However, neither m-chloro-phenylbiguanide, among the agonists, nor zacopride, among the antagonists, were able to prevent the effect of N-bromosuccinimide, suggesting that variations might exist in the molecular mechanisms implicated in the binding of 5-HT3 ligands to the recognition site on 5-HT3 receptors. Nevertheless, these data support the suggestion that tryptophan residue(s) are probably involved in the binding of agonists and antagonists onto 5-HT3 receptors in NG108-15 cell membranes.

Amino Acids↗
PubMed1999

The genetic basis of tetrathionate respiration in Salmonella typhimurium.

A range of bacteria are able to use tetrathionate as a terminal respiratory electron acceptor. Here we report the identification and characterization of the ttrRSBCA locus required for tetrathionate respiration in Salmonella typhimurium LT2a. The ttr genes are located within Salmonella pathogenicity island 2 at centisome 30.5. ttrA, ttrB and ttrC are the tetrathionate reductase structural genes. Sequence analysis suggests that TtrA contains a molybdopterin guanine dinucleotide cofactor and a [4Fe-4S] cluster, that TtrB binds four [4Fe-4S] clusters, and that TtrC is an integral membrane protein containing a quinol oxidation site. TtrA and TtrB are predicted to be anchored by TtrC to the periplasmic face of the cytoplasmic membrane implying a periplasmic site for tetrathionate reduction. It is inferred that the tetrathionate reductase, together with thiosulphate and polysulphide reductases, make up a previously unrecognized class of molybdopterin-dependent enzymes that carry out the reductive cleavage of sulphur-sulphur bonds. Cys-256 in TtrA is proposed to be the amino acid ligand to the molybdopterin cofactor. TtrS and TtrR are the sensor and response regulator components of a two-component regulatory system that is absolutely required for transcription of the ttrBCA operon. Expression of an active tetrathionate reduction system also requires the anoxia-responsive global transcriptional regulator Fnr. The ttrRSBCA gene cluster confers on Escherichia coli the ability to respire with tetrathionate as electron acceptor.

Amino Acid Sequence↗
PubMed1979

[Comparative tests of various liquid media for the preenrichment of salmonellae from milk powder (author's transl)].

In applying S. mendoza the following four liquid media were tested as to whether they can be used as enrichment broths for salmonellae in milk powder: phosphate buffered water, correspondingly buffered peptone broth, tetrathionate and selenite lactose broth. The yield of salmonellae in these tests is largely independent of the starting pH value of the prepared milk suspension which was varied between 5.8 and 8.2 (Fig. 1). In water the pH dropped within 24 hours (Fig. 2), in peptone and tetrathionate broth within 48 hours down to figures between 4.1 and 4.4 (Fig. 3 and 4), in selenite broth final figures of pH 5.7 were not attained before the lapse of 6 days (Fig. 5). The absolutely highest germ figures were observed in selenite broth. Quite in general the bacteria figure maximum was not attained until the 3rd--5th day, whereupon the germ figures dropped again. In peptone broth the introduced salmonellae were recovered in 73% of all cases after the lapse of 24 hours. Also in tetrathionate the success quota was about 73%, but part of it (8%) did not increase until a lapse of more than 72 hours incubation time, although the pH had already become strongly acid some days previously. In water the introduced salmonellae were traced only in 67%, in selenite broth even only in 61%. Also the time until the first detection increased a little in these media (Table 1). The period during which salmonellae were traceable was equally highest in peptone broth being 57% relative to the complete testing period (tetrathionate: 55%, water: 51%, selenite: 39% (Table 1). This permits the conclusion that peptone broth is the best preenrichment medium in which salmonellae may become traceable after a lapse of approx. 24 hours. Not considerably more unfavourable is the tetrathionate broth which so far had been considered as an exclusive selectivity medium. In this context it is, however, necessary to face the possibility that predamaged salmonellae do not begin to increase until the end of some days incubation and even at a strongly acid pH.

Animals↗
PubMed2006

A novel gene cluster soxSRT is essential for the chemolithotrophic oxidation of thiosulfate and tetrathionate by Pseudaminobacter salicylatoxidans KCT001.

Chemolithotrophic sulfur oxidation (Sox) in the alpha-proteobacterium Pseudaminobacter salicylatoxidans KCT001 was found to be governed by the gene cluster soxSRT-soxVWXYZABCD. Independent transposon-insertion mutations in the genes soxB, soxC, soxD, and also in a novel open reading frame (ORF), designated as soxT, afforded revelation of the entire sox locus of this bacterium. The deduced amino acid sequence of the novel ORF soxT comprised 362 residues and exhibited significant homology with hypothetical proteins of diverse origin, including a permease-like transport protein of Escherichia coli. Two contiguous ORFs, soxR and soxS, immediately preceded the soxT gene. The gene cluster soxSRT was located upstream of soxVWXYZABCD and was transcribed divergently with respect to the latter. Chemolithotrophic utilization of both thiosulfate and tetrathionate was observed to have been impaired in all of these Sox- mutants, implicating the involvement of the gene cluster soxSRT-soxVWXYZABCD in the oxidation of both thiosulfate and tetrathionate.

Alphaproteobacteria↗
PubMed2004

Dispersion relations for the convective instability of an acidity front in Hele-Shaw cells.

Autocatalytic chemical fronts of the chlorite-tetrathionate (CT) reaction become buoyantly unstable when they travel downwards in the gravity field because they imply an unfavorable density stratification of heavier products on top of lighter reactants. When such a density fingering instability occurs in extended Hele-Shaw cells, several fingers appear at onset which can be characterized by dispersion relations giving the growth rate of the perturbations as a function of their wave number. We analyze here theoretically such dispersion curves comparing the results for various models obtained by coupling Darcy's law or Brinkman's equation to either a one-variable reaction-diffusion model for the CT reaction or an eikonal equation. Our theoretical results are compared to recent experimental data.

Journal Article↗
PubMed1982

Interactions of the chelating agent 2,3-dimercaptopropane-1-sulfonate with red blood cells in vitro. I. Evidence for carrier mediated transport.

Uptake of the water soluble 1,2-dimercaptopropanol (BAL) derivative 2,3-dimercapto-1-sulfonate (DMPS) into human red blood cells was found in vitro and the mode of penetration studied in detail. The compound entered erythrocytes in a concentration dependent manner. In contrast to sealed ghosts where inside and outside concentrations reached the same value, DMPS accumulated in intact erythrocytes. Since no binding of DMPS could be detected, the reason for accumulation was assumed to be a conversion of DMPS into chelates or metabolites which penetrated the membrane in a slower rate. A facilitated transport of DMPS mediated by the anion carrier protein was concluded on the basis of the following similarities with the anion transport: inhibition of [14C]DMPS-uptake by N-ethylmaleimide (NEM), tetrathionate (90%), sulfate (50%), 5,5'-dithio bis(2-nitrobenzoic acid) (DTNB) (25%); inhibition of uptake and efflux by 4,4'-diisothiocyano-2,2'-stilbene disulfonate (DIDS) (80%), dipyridamole (55%); temperature dependency (activation energy 24 Kcal/mol); pH-dependency (pH optimum about 6.9); counter-transport; activation of uptake by preincubation with DMPS (transmembrane effect).

Cell Membrane↗
PubMed1985

High-molecular-weight renin converting enzyme from dog kidney: detection and fractionation.

Renal cortical high-molecular-weight renin (Mw:60,000) of the dog is a complex of renin (low-molecular-weight renin; Mw:40,000) and a renin binding protein. We detected an enzyme-like substance that catalyzes the conversion from high- into low-molecular-weight renin. When the renal cortical extract was added to the high-molecular-weight renin and the preparation incubated at 37 degrees C for 30 min, the high-molecular-weight renin was converted into the low-molecular-weight form. No such conversion occurred in the case of renal medullary extract. This converting substance was fractionated using concanavalin A Sepharose, 70% ammonium sulfate saturation and DEAE-cellulose chromatography. The converting activity was inhibited by potassium tetrathionate, N-ethylmaleimide and 5,5'-dithiobis-(2-nitrobenzoic acid). These events suggest that this substance is an enzyme possessing sulfhydryl moieties. However, a cathepsin B inhibitor leupeptin did not affect the activity. Accordingly, the high-molecular-weight renin converting enzyme, which is sensitive to sulfhydryl oxidation, may explain the mechanism of interconversion between high- and low-molecular-weight renin involving the oxidation-reduction of tissue sulfhydryl groups.

Animals↗
PubMed2001

Role for outer membrane cytochromes OmcA and OmcB of Shewanella putrefaciens MR-1 in reduction of manganese dioxide.

Shewanella putrefaciens MR-1 can use a wide variety of terminal electron acceptors for anaerobic respiration, including certain insoluble manganese and iron oxides. To examine whether the outer membrane (OM) cytochromes of MR-1 play a role in Mn(IV) and Fe(III) reduction, mutants lacking the OM cytochrome OmcA or OmcB were isolated by gene replacement. Southern blotting and PCR confirmed replacement of the omcA and omcB genes, respectively, and reverse transcription-PCR analysis demonstrated loss of the respective mRNAs, whereas mRNAs for upstream and downstream genes were retained. The omcA mutant (OMCA1) resembled MR-1 in its growth on trimethylamine N-oxide (TMAO), dimethyl sulfoxide, nitrate, fumarate, thiosulfate, and tetrathionate and its reduction of nitrate, nitrite, ferric citrate, FeOOH, and anthraquinone-2,6-disulfonic acid. Similarly, the omcB mutant (OMCB1) grew on fumarate, nitrate, TMAO, and thiosulfate and reduced ferric citrate and FeOOH. However, OMCA1 and OMCB1 were 45 and 75% slower than MR-1, respectively, at reducing MnO(2). OMCA1 lacked only OmcA. While OMCB1 lacked OmcB, other OM cytochromes were also missing or markedly depressed. The total cytochrome content of the OM of OMCB1 was less than 15% of that of MR-1. Western blots demonstrated that OMCB1 still synthesized OmcA, but most of it was localized in the cytoplasmic membrane and soluble fractions rather than in the OM. OMCB1 had therefore lost the ability to properly localize multiple OM cytochromes to the OM. Together, the results suggest that the OM cytochromes of MR-1 participate in the reduction of Mn(IV) but are not required for the reduction of Fe(III) or other electron acceptors.

Amino Acid Sequence↗
PubMed1984

Reaction of phenylhydrazine with erythrocytes. Cross-linking of spectrin by disulfide exchange with oxidized hemoglobin.

Phenylhydrazine causes deleterious oxidations of components of erythrocytes. These reactions and their effects on the mechanical properties of rabbit erythrocytes are investigated to provide insight into the mechanisms leading to destruction of oxidatively damaged erythrocytes. After 1 hr of incubation with phenylhydrazine, precipitated denatured protein (Heinz body protein) amounts to 25-30% of membrane protein, but deformability of erythrocytes as measured by filtrability is unchanged. After 4 hr of incubation filtrability drops sharply. Polymerization of spectrin and covalent binding of hemoglobin to spectrin, but no peroxidation of membrane lipids is observed. Precipitated protein amounts to 85-95% of membrane protein. It contains Fe, porphyrin and globin peptide in the proportion 1:1:1. Heinz body protein precipitated when hemoglobin is incubated under similar conditions has 90% of its sulfhydryl groups oxidized and no other amino acids than cysteine are destroyed. Addition of this Heinz body protein to erythrocyte ghosts causes polymerization of spectrin. Incubation of tetrathionate, a specific cross-linking agent, causes filtrability to drop sharply after about 80 min. This effect is similar to that observed after 4 hr incubation with phenylhydrazine, and is accompanied by polymerization of spectrin and band 3. The results indicate that cross-linking of membrane proteins by disulfide exchange with precipitated hemoglobin may play a major role in decreasing deformability during incubation with phenylhydrazine.

Amino Acids↗
PubMed1975

Photosensitized inactivation of stem bromelain. Oxidation of histidine, methionine, and tryptophan residues.

Pineapple stem bromelain was photooxidized in the presence of Methylene Blue used as a sensitizer. The essential sulfhydryl group of the enzyme protein rapidly became inaccessible to react with 5,5'-dithiobis(nitrobenzoic acid), but the reactivity was readily regained to the original level upon treatment with dithiothreitol. Even after such reduction, the photooxidized enzyme showed a markedly decreased hydrolytic activity on casein. Spectral examination revealed that the oxidized enzyme had tyrosine residues intact. Amino acid analysis showed significant decreases in histidine, ethionine, and tryptophan residues. Photoinactivation occurred in a similar manner also in the presence of tetrathionate which reversibly blocked the essential sulfhydryl group. It is concluded that the irreversible photoinactivation of stem bromelain must be related to the oxidation of histidine, methionine, and tryptophan residues. When the photooxidation was carried out a different pH values ranging from 4.0 to 8.3, the inactivation and the decrease in histidine content were found to be markedly pH dependent. Thus, the photooxidation experiment provided a method for directly measuring the apparent pKa of the ionization of the single histidine residue in stem bromelain. Apparent pKa values of 6.4 and 7.1 were obtained for the histidine imidazole in the absence and in presence of tetrathionate, respectively. In view of these normal pKa values for an imidazole, a mechanism of ionization of the active-site group in a plant thiol proteinase is proposed, in which the validity of mechanism involving a close electronic interaction between histidine and cysteine residues is seriously questioned.

Amino Acids↗