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PubMed1996

Insertion of the polytopic membrane protein MalF is dependent on the bacterial secretion machinery.

We examined the dependence of protein export and membrane protein insertion on SecE and SecA, two components of the secretion (Sec) apparatus of Escherichia coli. The magnitude of the secretion defect observed for signal sequence-containing proteins in cells depleted of SecE is larger and more general than that in many temperature- or cold-sensitive Sec mutants. In addition, we show that the proper insertion of the polytopic MalF protein (synthesized without a signal sequence) into the cytoplasmic membrane is also SecE-dependent. In contrast to an earlier study (McGovern, K., and Beckwith, J. (1991) J. Biol. Chem. 266, 20870-20876), the membrane insertion of MalF also is inhibited by treatment of cells with sodium azide, a potent inhibitor of SecA. Therefore, our data strongly suggest that the cytoplasmic membrane insertion of MalF is dependent on the same cellular machinery as is involved in the export of signal sequence-containing proteins. We propose that the mechanism of export from the cytoplasm is related for both signal sequence-containing and cytoplasmic membrane proteins, but hydrophobic membrane proteins such as MalF may have a higher affinity for the Sec apparatus.

ATP-Binding Cassette Transporters↗

PubMed1991

Induction of chromosomal aberrations with the restriction endonuclease AluI in Chinese hamster ovary cells: comparison of different treatment methods.

Chinese hamster ovary (CHO) cells were treated with the restriction endonuclease AluI using various methods; namely, treatment in the presence of hypertonic concentrations of glycerol or sorbitol and electroporation. The frequencies of chromosomal aberrations induced were scored in first post-treatment metaphases. For all treatment schedules linear dose-effect relationships of polycentric chromosomes were found. The distribution of polycentric chromosomes induced by AluI was overdispersed. Inhibition of cellular energy metabolism with sodium azide and 2-deoxyglucose led to a strong reduction of the frequencies of chromosomal aberrations when the treatment with AluI was carried out in the presence of glycerol or sorbitol, but not when carried out by electroporation. This is interpreted to mean that glycerol- or sorbitol-mediated cellular uptake of AluI, but not the uptake via electroporation, is an energy-dependent mechanism.

Animals↗

PubMed1988

Priming activity for chemiluminescence reaction of PMN in the culture supernatant of streptococcal preparation (OK-432)-stimulated spleen cells.

We investigated the effect of supernatant from human spleen cell culture stimulated with a streptococcal preparation, OK-432 (OK sup), on the luminol-dependent chemiluminescence (CL) of human polymorphonuclear leukocytes (PMN). The fMLP-stimulated CL of PMN was markedly enhanced by the pretreatment with OK sup. This result indicates that OK sup contained the factor(s) that primes fMLP-stimulated CL of PMN. The priming factor(s) in OK sup was partially inactivated by the treatment at 56 C for 30 min and pH 2 or pH 10 treatments. Since the enhancing effect of OK sup on the CL was inhibited by the treatment of sodium azide and the addition of catalase or taurine, it was assumed that OK sup augments the activity of MPO-H2O2-HOCl system of fMLP-stimulated PMN.

Azides↗

PubMed1996

The bound adenine nucleotides of purified bovine mitochondrial ATP synthase.

The experiments in this study were directed towards defining the nucleotide content of purified beef-heart mitochondrial F1F0 ATP synthase during binding and hydrolysis of ATP. The purified, soluble synthase as prepared contained 2 mol ATP and 2 mol ADP/mol enzyme. Three of these four nucleotides were exchangeable on incubation with radiolabelled MgATP. Passage of the ATP synthase through a column of Sephadex G-50 readily removed 1 mol ADP/mol. The remaining bound nucleotides were not displaced by incubation with 1 mM GTP or 5 mM sodium sulfite, the latter an activator of the ATPase activity of the synthase. Incubation of the synthase with 250 microM MgATP in the presence of 3 mM sodium azide, an inhibitor of the ATPase, resulted in the transitory formation of a form of the enzyme in which 5-6 nucleotide-binding sites were loaded with ATP and/or ADP, thus showing that the ATP synthase, like the soluble F1 ATPase, contained a minimum of six nucleotide-binding sites. The presence of an ATP-regenerating system during incubation with MgATP resulted in the loading of 5-6 sites to yield a form of the enzyme containing 3-4 mol ATP and 2 mol ADP/mol synthase even after passage through a centrifuged column. Following hydrolysis of the medium MgATP, the enzyme reached a stable form containing 2 mol ATP and 2 mol ADP/mol synthase. Like the form of the enzyme originally prepared, 1 mol ADP/mol synthase was readily released. However, this ADP remained bound to the synthase in the presence of GTP if azide was present. These results are discussed in the context of current ideas about nucleotide-binding sites on the F1 ATPase portion of the F1F0 ATP synthase. It is concluded that the properties of the sites on the F1F0 synthase show some differences from those on the F1 ATPase.

Adenosine Diphosphate↗

PubMed1989

Differential control and calcium-dependence of production of endothelium-derived relaxing factor and prostacyclin by pig aortic endothelial cells.

1. Production of endothelium-derived relaxing factor (EDRF) by primary cultures of pig aortic endothelial cells was assessed indirectly by measuring endothelial cyclic GMP content, and prostacyclin production was measured by radioimmunoassay of 6-keto prostaglandin F1 alpha (6-keto PGF1 alpha). 2. The resting level of cyclic GMP fell significantly following removal of extracellular calcium (1 mM EGTA present), but elevations of cyclic GMP content induced by sodium azide (10 microM) or atriopeptin II (10 nM) were similar in the absence and presence of extracellular calcium. 3. Haemoglobin (10 microM) reduced the resting level of cyclic GMP in the presence, but not the absence of extracellular calcium. M&B 22,948 (100 microM), superoxide dismutase (30 u ml-1), bradykinin (0.1 microM), ATP (10 microM) and ionophore A23187 (0.1 microM) each induced an increase in endothelial cyclic GMP content that was reduced in the absence of extracellular calcium. 4. In cascade bioassay experiments using endothelial cells on microcarrier beads and perfused in columns, continuous infusion of bradykinin (0.1 microM) induced release of EDRF, assayed on rabbit aortic rings, that was maximal after 2 min and still detectable up to about 16 min. 5. In the presence of extracellular calcium, the time course of bradykinin (0.1 microM)-stimulated production of EDRF, assessed as endothelial cyclic GMP content was maximal within 1 min, declined thereafter, but was still significant after 30 min. Production of 6-keto PGF1 alpha, measured simultaneously rose rapidly but was complete within 3 min. 6. In the absence of extracellular calcium the resting endothelial content of cyclic GMP fell, but resting production of 6-keto PGF1 alpha was unaffected. 7. In the presence of TMB-8 (100 microM) resting endothelial content of cyclic GMP rose slightly, but production of 6-keto PGFg fell. The bradykinin (0.1 microM)-stimulated increase in cyclic GMP content was augmented, but the stimulation of 6-keto PGF1I production was blocked. Results from cascade bioassay experiments confirmed that TMB-8 (100 microM) did not inhibit bradykinin-induced production of EDRF. 8. The data suggest that resting production of EDRF but not prostacyclin is dependent upon the presence of extracellular calcium. Bradykinin-stimulated production of EDRF is sustained and requires the presence of extracellular calcium, but stimulated production of prostacyclin is transient and may result from discharge of an intracellular pool of calcium. 9. The vascular endothelial cell appears therefore to control differentially production of EDRF and prostacyclin.

Adenosine Triphosphate↗

PubMed1990

Energy and calcium ion dependence of proteolysis during sporulation of Bacillus subtilis cells.

Bacterial cells degrade intracellular proteins at elevated rates during starvation and can selectively degrade proteins by energy-dependent processes. Sporulating bacteria can degrade protein with apparent first-order rate constants of over 0.20 h-1. We have shown, with an optimized [14C]leucine-labeling and chasing procedure, in a chemically defined sporulation medium, that intracellular protein degradation in sporulating cells of Bacillus subtilis 168 (trpC2) is apparently energy dependent. Sodium arsenate, sodium azide, carbonyl cyanide m-chlorophenylhydrozone, and N,N'-dicyclohexylcarbodiimide, at levels which did not induce appreciable lysis (less than or equal to 10%) over 10-h periods of sporulation, inhibited intracellular proteolysis by 13 to 93%. Exponentially growing cells acquired arsenate resistance. In contrast to earlier reports, we found that chloramphenicol (100 micrograms/ml) strongly inhibited proteolysis (68%) even when added 6 h into the sporulation process. Restricting the calcium ion concentration (less than 2 microM) in the medium had no effect on rates or extent of vegetative growth, strongly inhibited sporulation (98%), and inhibited rates of proteolysis by 60% or more. Inhibitors of energy metabolism, at the same levels which inhibited proteolysis, did not affect the rate or degree of uptake of Ca2+ by cells, which suggested that the Ca2+ and metabolic energy requirements of proteolysis were independent. Restricting the Ca2+ concentration in the medium reduced by threefold the specific activity in cells of the major intracellular serine proteinase after 12 h of sporulation. Finally, cells of a mutant of B. subtilis bearing an insertionally inactivated gene for the Ca2(+)-dependent intracellular proteinase-1 degraded protein in chemically defined sporulation medium at a rate indistinguishable from that of the wild-type cells for periods of 8 h.

Arsenates↗

PubMed1988

Magnetic resonance studies of intact human spermatozoa.

A correlation has been established between the ability of sperms to reduce the nitroxide spin label--TEMPO and their metabolic activity. The rate of reduction of TEMPO is sensitive to the quantity and quality of sperms and therefore, this property can be developed into a quality rating method. Keeping this in mind, effects of various agents on the spin label reduction rates have been studied. The effect of cold shock on sperms has been found to be harmless and does not lead to loss in metabolic activity. The differential rates of spin label reduction after bubbling N2 and O2 gases through the samples indicate that the process of anaerobic glycolysis imparts higher electron donating capacity to spermatozoa. The method has been used to study influence of inhibitors of electron transport chain (ETC) such as rotenone, antimycin A, KCN and sodium azide which inhibit ETC at different levels.

Antimycin A↗

PubMed1984

Effects of leukotrienes and f-Met-Leu-Phe on oxidative metabolism of neutrophils and eosinophils.

We assessed the effects of several leukotrienes and of f-Met-Leu-Phe on oxygen consumption in neutrophils and on the initial burst of chemiluminescence (CL) in both neutrophils and eosinophils. It was found that f-Met-Leu-Phe initiated 2.6 times higher oxygen consumption in neutrophils than did leukotriene B4 (LTB4). f-Met-Leu-Phe also stimulated five to 10 times more CL from both types of granulocytes than LTB4, which was at least five times more potent than its omega-hydroxylated metabolite, 20-OH-LTB4, whereas the corresponding 20-COOH derivative was effective only in eosinophils. The double dioxygenation product 5(S), 12(S)- DHETE caused no CL. Neutrophils from patients with chronic granulomatous disease did not respond with CL to any of the agents. The peak of CL occurred 50 to 60 sec after the addition of fMLP, whereas the LTB4-associated peak occurred after 5 to 6 sec and then rapidly subsided. The treatment of cells with sodium azide to inhibit the myeloperoxidase system did not change the kinetics or the rapid decline of the LTB4-induced CL. The CL response to LTB4 could be inhibited to 85% by 0.5 microgram/ml of superoxide dismutase, to 72% by 200 mg/ml of catalase, and to 50% by 80 microM of mannitol. The corresponding figures for f-Met-Leu-Phe-induced CL were 80, 58, and 16%, suggesting that, although a substantial part of the CL appears to be due to superoxide ion production, other oxygen radicals are involved in luminol-enhanced CL production. Thus, in contrast to some previous reports that leukotrienes do not stimulate an oxidative metabolic response in granulocytes despite their potent activity as chemotactic factors, our studies show that leukotrienes are definite inducers of granulocyte oxidative metabolism.

Azides↗

PubMed1982

[Ability to redistribute surface receptors in transplantable cell lines].

The ability of cultured lymphoid, erythroid and fibroblastic cells for ligand-induced redistribution of their surface receptors proved to be lower than that of lymphocytes. The process of surface receptors redistribution can be inhibited by low temperature and sodium azide in all the cells under study. Pretreatment with trypsin increased the ability for redistribution of surface receptors in some types of cultured cells, but had no such effect on lymphocytes. These differences between lymphocytes and cultured cells seem to be due to differences in organization of the surface and contractile systems of the respective cells.

Animals↗

PubMedDate not supplied

[Activity and properties of superoxide dismutase from human erythrocytes and plasma in ontogenesis].

One- and two-substituted potassium-salts of phosphoric acid are studied for their effect on the value of superoxide dismutase (SOD) activity in the plasma and erythrocytes of healthy adults and newborn children. It is shown that the superoxide dismutase activity of plasma depends on the phosphoric acid salts which are used during its treatment. Single direction of changes in the activity of superoxide dismutase obtained after the plasma treatment by KH2PO4 and K2HPO4 depending on the pH incubation medium, the results of separation of protein fractions obtained by the method of disc-electrophoresis testify that the superoxide dismutase activity is connected with the same protein. Different absolute values of the plasma SOD activity and different influence on it of azide sodium are, probably, determined by spatial orientation of copper ions in the active centre, which changes depending on pH of the medium. Superoxide dismutase plasma and erythrocytes in newborn children have higher activity than is adults.

Adolescent↗

PubMed1986

Evidence for and partial characterization of three major and three minor chromatographic forms of human neutrophil myeloperoxidase.

Myeloperoxidase (MPO) is an enzyme found in the azurophil granules of neutrophils. Cation-exchange chromatography on carboxymethyl-cellulose previously has been used to demonstrate the heterogeneity of the peroxidase enzymes isolated from human neutrophils. In this study, fast protein liquid chromatography (FPLC) was used to separate and purify three major (I, II, and III) and three minor (IIa, IIIa, IIIb) forms of MPO from isolated neutrophil granules. Purity was confirmed by polyacrylamide gel electrophoresis in the presence of cetyltrimethylammonium bromide (CETAB-PAGE), by crossed immunoelectrophoresis, and by spectral characteristics. All three major forms were indistinguishable by immunodiffusion against rabbit antiserum, scanning spectrophotometry, and amino acid composition. They differed in their elution from a cation-exchange resin, inhibition by 3-amino-1,2,4-triazole, migration rate in CETAB-PAGE, and subunit molecular weight. Subunit molecular weight was examined using sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). All three major forms appeared to consist of heavy (H), intermediate (M), and light (L) peptides. The M peptide appeared to be derived from the H subunit. All L subunits exhibited a molecular weight of 14,500. The molecular weights for the H subunits varied, and were 60,000, 59,000, and 57,000 for MPO I, II, and III, respectively. The molecular weights for the M peptides were 44,100, 43,000, and 42,000 for MPO I, II, and III, respectively. The treatment of neutrophils, granules, and extracts with protease inhibitors and sodium azide did not block the appearance of three major forms of MPO. Thus, neither protease activity nor MPO autooxidation during extraction and purification procedures is responsible for the appearance of multiple chromatographic forms of MPO derived from human neutrophils.

Amino Acids↗

PubMed1990

Human immunodeficiency virus I-induced expression of P-glycoprotein.

Because prolonged treatment of HIV infection with 3'-azido-3'-deoxythymidine (AZT) is associated with in vitro resistance to AZT, we examined whether HIV could induce/amplify the expression of p-glycoprotein in infected cells resulting in reduced drug accumulation leading to reduced sensitivity to AZT. We show that both H9 (T cell line) and U937 (monocytic cell line) cells, upon infection with HIV, expressed increased levels of P-glycoprotein and accumulated significantly less AZT and daunorubicin as compared to uninfected cells. Sodium azide increased intracellular accumulation of daunorubicin in infected cells, suggesting a metabolically active drug efflux mechanism. Addition of cyclosporin A partially corrected intracellular drug accumulation in HIV infected cells. In addition, similar to multidrug resistant tumor cells, HIV-infected cells show depolarization of plasma membrane. Taken together, these data suggest that HIV-induced increased P-glycoprotein expression could be one of the mechanisms for reduced intracellular accumulation of antiviral agents and resistance to AZT and perhaps to other anti-retroviral agents.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMed1986

Eosinophil-mediated cellular cytotoxicity induced by zymosan-activated serum.

The aim of the present work was to develop an in vitro model of eosinophil cytotoxicity which mimics numerous in vivo situations characterized by complement activation through the alternative pathway. Our results demonstrate that eosinophilic granulocytes from patients with parasitic diseases and blood eosinophilia were able to damage chicken red blood cells when incubated with zymosan-activated serum (ZAS) as assessed by a 51Cr release assay. The phenomenon was independent of the presence of antibodies directed against the target cells and related to the quantity of ZAS added to the wells. As target cell lysis is totally or partially inhibited by catalase, sodium azide and potassium cyanide, an involvement of toxic oxygen derivatives as cytolytic mediators was suggested.

Azides↗

PubMed1987

Biochemical studies on the catalysis of nitrosation by bacteria.

Biochemical and microbiological studies were conducted to characterize the mechanism of bacterial formation of N-nitrosomorpholine from morpholine and nitrite at neutral pH. Nitrosating activity was markedly induced when bacteria were cultured anaerobically in minimal culture medium containing nitrate, while the presence of cysteine or tungsten in the medium inhibited induction. Of various metals, coenzymes and inhibitors tested for their effects on in vitro nitrosation of morpholine, potassium cyanide, sodium azide, NAD(P)H and nitrate strongly inhibited nitrosation. Several mutants of Escherichia coli A10 strain were prepared in order to examine whether nitrosation activity is linked to specific loci. Niridazole-resistant mutants, which lack nitroreductase, had as much nitrosating activity as the original E. coli A10, but chlorate-resistant mutants had completely lost this activity. A good correlation was observed between nitrate reductase activity and nitrosating activity in these mutants. These results indicate that bacterial nitrosation is an enzyme-mediated reaction closely associated with molybdenoenzymes such as the nitrate reductase/formate hydrogenlyase system.

Azides↗

PubMed1996

Osteoclast demise in the rat: physiological versus degenerative cell death.

Time-lapse video microscopy was used to assess the temporal morphological events undergone by rat osteoclasts after exposure to a variety of agents that promote cell death. Direct observations revealed that there were two morphologically distinguishable forms of cell death, which resembled apoptosis and necrosis, respectively. Marked changes in morphology became apparent after 2-4 h exposure to a variety of agents, including cyclosporine A, tamoxifen, corticosterone and dexamethasone. The cells began to shrink rapidly and within 25 min appeared as small round spheres. At this time, the cell membranes underwent violent distortive boiling, or zeiosis, accompanied by the formation of small membrane buds. The cells maintained a spherical configuration and the membrane appeared to remain intact for several hours. These observations are consistent with the process of physiological cell death or apoptosis. In some cases, post-apoptotic changes or secondary necrosis could be seen, including membrane blebbing and degeneration. In contrast, when cells were exposed to hydrogen peroxide or sodium azide, there was a marked deterioration of the cell membrane after 1-4h. This included the formation of spikes and/or blebbing with the release of intracellular debris, resulting in an overall spattered appearance. This type of appearance is characteristic of degenerative cell death or necrosis. The significance of the mode of osteoclast death is discussed.

Animals↗

PubMed1996

Performance of urea-sensitive enzyme field effect transistors: influence of the storage conditions.

Urea-sensitive enzyme field effect transistors (ENFETs) were prepared by cross-linking urease with bovine serum albumin in saturated glutaraldehyde vapor on the sensitive surface of a pH-FET. The linear part of the biosensor dynamic range is between 5 x 10(-5) and 10(-3) M of urea. The influence of pH on the sensor response, stability and reproducibility of the urea sensor were examined. The addition of EDTA, glycerol, sodium azide and dithiothreitol in the storage buffer solution was studied. In these specific storage conditions, an increase of sensor sensitivity and stability was observed, which means that the enzyme is inhibited during the immobilisation procedure and can be partially restored. Furthermore such reagents do not affect the operational characteristics of the sensor when working in serum.

Azides↗

PubMed1988

Dynamic behavior of the transferrin receptor followed in living epidermoid carcinoma (A431) cells with nanovid microscopy.

Transferrin receptors labeled with the B3/25 monoclonal antibody-gold complexes were followed in living A431 cells by using video-enhanced contrast microscopy. Initially, the antibody-gold complexes bind to receptors which are freely mobile on the upper cell surface; they then become trapped at the inner margins of the peripheral lamellae and internalize. During endocytosis discrete gold-loaded vesicular elements first appear, and then, as they fuse, a heterogenous peripheral endosomal compartment forms. The endosomes from this compartment then begin to migrate centripetally through the cytoplasm in a saltatory way so that within 15 min gold label accumulates in a juxtanuclear endosome compartment. This compartment, which consists mainly of multivesicular bodies, is thus formed by the influx and retention of peripheral endosomal elements and their continued fusion in the juxtanuclear area. Although their overall migration is inward, saltating endosomes frequently reverse their direction of movement. As label builds up in the juxtanuclear area, small vesicles containing gold label continuously pinch off from the larger elements and migrate toward the cell periphery. Experiments with nocodazole and sodium azide show that the saltatory movements, the accumulation and retention of endosomes in the juxtanuclear area, and the separation of vesicles from endosomes are driven by a microtubule-associated, ATP-dependent, motility-generating mechanism. Analysis of the movements shows that although each individual vesicle saltation can occur unpredictably toward the centre or the periphery of the cell, a net centripetal flux is observed. Moreover, it is evident that the probability of migration toward and maintenance in the juxtanuclear area is related to the diameter of the vesicles. We propose a mechanism by which bidirectional saltation along microtubules forming a radial network may be instrumental in the selective concentration of large endosomes in the juxtanuclear area while small vesicles are left free to return to the periphery. This process may be responsible for the sorting of receptors and ligands destined either for intracellular degradation in juxtanuclear lysosomes or, alternatively, for recycling to the plasma membrane.

Alkaloids↗

PubMed1996

Cellular uptake of trivalent arsenite and pentavalent arsenate in KB cells cultured in phosphate-free medium.

Trivalent arsenite (As(III)) and pentavalent arsenate (As(V)) have been shown to have differential uptake mechanisms. In regular RPMI 1640 medium, As(III) was about 40-fold more toxic to KB oral epidermoid carcinoma cells. However, the cytotoxicity and intracellular accumulation of As(V) were dramatically enhanced, equalling those of As(III) when cells were grown in phosphate-free RPMI medium, As(V) uptake was dose-dependently inhibited by phosphate, mersalyl acid (a membrane sulfhydryl agent), and energy poisons, such as sodium azide and potassium cyanide. These results suggest that As(V) and phosphate share a common transport system. In contrast, As(III) uptake was not affected by the above agents. However, the initial uptake rates of As(III) were linearly correlated with its extracellular concentrations, suggesting that As(III) uptake is probably accomplished through simple diffusion. Our results also show that As(III) and As(V) are excreted from KB cells at a comparable rate, and at least half of As(V) is reduced to the more toxic As(III) prior to excretion into the medium. Therefore, the toxicity of As(V) may in part result from its reduction to As(III).

Arsenates↗