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PubMed1985

Differential effects of triphenyltin and 8-azido-ATP on the ATP synthesis, ATP-Pi exchange, and ATP hydrolysis in liposomes containing ATP synthase and bacteriorhodopsin.

The ATP hydrolysis activity of purified ATP synthase reconstituted in liposomes was inhibited by triphenyltin in a manner different from that of other thiol-specific reagents. In liposomes containing ATP synthase and bacteriorhodopsin, ATP hydrolysis and ATP-Pi exchange were inhibited by triphenyltin to a greater extent than the ATP synthesis, in contrast to what was found with an F1-specific inhibitor, 8-azido-ATP. The possibility is discussed that ATP hydrolysis and ATP synthesis are differently coupled to proton conduction through F0.

Adenosine Triphosphate↗
PubMed1985

Transient proton inflows during illumination of anaerobic Halobacterium halobium cells.

In Halobacterium halobium strain R1 containing both bacteriorhodopsin (bR) and halorhodopsin (hR), the light-driven proton uptake has been experimentally resolved into three transient inflows which are superimposed on the larger proton outflow. Under anaerobic conditions the early proton uptake consists of two components: (i) an inflow which can be blocked using the ATPase inhibitor, Dio-9, and (ii) an inflow which can be abolished by low concentrations (less than 125 nM) of triphenyltin chloride (TPT) with no inhibition of ATP synthesis. At pH 6 these two inflows are approximately equal in magnitude and duration. Measurements of buffering capacity and internal pH indicate that Dio-9 does not alter the passive proton-hydroxyl permeability of the cell membrane and that TPT at these low concentrations slightly decreases it. At later times of illumination (iii) another transient light-driven proton inflow occurs. This inflow is most evident during the first illumination after cells have been stored for extended times in the dark. The internal potassium concentration is not changed by storage, but apparently sodium is taken up, and we attribute the third inflow to sodium extrusion in exchange for protons. These results demonstrate the existence of three distinct triggered secondary proton inflows through the cell membrane. The proton inflow, which can be inhibited by Dio-9, correlates with proton-dependent ATP synthesis. The second inflow, which disappears in the presence of low TPT concentrations, is a passive proton uptake through an otherwise unidentified channel in response to electrogenic chloride pumping by bacteriorhodopsin and/or halorhodopsin. The third system correlates with the Na+/H+ antiporter function that has been demonstrated in H. halobium cell envelope vesicles. In contrast to observations on hR-containing vesicles, which can develop substantial Cl- gradients, the electroneutral OH-/Cl- exchange function can be demonstrated in intact cells only at TPT concentrations greater than 500 nM.

Adenosine Triphosphate↗
PubMed1983

All-or-none interactions of inhibitors of the plasma membrane ATPase with Saccharomyces cerevisiae.

The inhibitors of the yeast plasma membrane ATPase, Dio-9, miconazole, suloctidil, N,N'-dicyclohexycarbodiimide, triphenyltin and diethylstilbestrol provoke an all-or-none K+ loss from the cells. Some of the K+-depleted cells also show an increased permeability for the dye, Bromophenol blue, indicating that the barrier properties of these cells are drastically changed. Apart from this all-or-none process, a graded loss of K+ is also observed. These observations warn against the use of the inhibitors in studies aimed at evaluating the role of the ATPase in the energy transduction of membrane transport processes of yeasts.

Adenosine Triphosphatases↗
PubMed1992

The role of anion channels in the mechanism of acrosome reaction in bull spermatozoa.

The involvement of anion channels in the mechanism of the acrosome reaction (AR) was investigated. The AR was induced by Ca2+ or by addition of the Ca2+ ionophore A23187. The occurrence of AR was determined by following the release of acrosin from the cells. In order to investigate the role of anion channels in the AR, several anion-channel inhibitors were tested, mainly DIDS (4,4'-diisothiocyanostilbene-2,2'-disulfonic acid). Other blockers, like SITS (4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid), furosemide, probenecid and pyridoxal 5-phosphate, were also tested. We found that DIDS binds covalently to sperm plasma membrane in a time- and concentration-dependent manner. Maximal binding occurs after 2 h with 0.3 mM DIDS. DIDS and SITS inhibit AR in a concentration-dependent manner. The IC50 of DIDS and SITS in the presence of A23187 is 0.15 and 0.22 mM, respectively. Tributyltin chloride (TBTC), an Cl-/OH- exchanger, partially overcomes DIDS inhibition of the AR. HCO3- is required for a maximal acrosin release and Ca(2+)-uptake, in the presence or absence of A23187. It is known that HCO3- activates adenylate cyclase and therefore, increases the intracellular level of cAMP. The inhibition of the AR by DIDS decreases from 95 to 50% when (dibutyryl cyclic AMP (dbcAMP) was added, i.e., HCO3- is no longer required while elevating the level of cAMP in an alternative way. Moreover, we show that the stimulatory effect of HCO3- on Ca(2+)-uptake is completely inhibited by DIDS. We conclude that DIDS inhibits AR by blocking anion channels, including those that transport HCO3- into the cell.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1992

Organotin-flavone complexes: a new class of fluorescent probes for F1F0ATPase.

Fluorescent 5-coordinate organotin-flavone complexes of 3-hydroxy-flavone (Hof) and 3,5,7,2',4',-pentahydroxyflavone (morin) are good inhibitors of mitochondrial F1F0ATPase but do not inhibit F1-ATPase and they have been examined as possible fluorescent probes of F1F0ATPase. R2SnX (morin) complexes exhibit low fluorescence enhancement on binding to mitochondrial membranes with no displacement by equimolar tributyltin. In contrast R2SnX (of) complexes exhibit high fluorescence enhancement whose extent is variable and is displacable by equimolar tributyltin. Fluorescence enhancement by R2SnX (of) complexes correlates with the ATPase I50 values. Dialkyltin-3-hydroxy flavone, R2SnX(of), complexes act as a new class of fluorescent probes which titrate the F0 segment of F1F0ATPase.

Animals↗
PubMed1983

Triphenyltin fluoride in vitro inhibition of rabbit platelet collagen-induced aggregation and ATP secretion and blockade of arachidonic acid mobilization from membrane phospholipids.

Recent studies have demonstrated that triphenyltin fluoride (TPTF) inhibits collagen-induced aggregation and ATP secretion of rabbit platelets in vivo [S. Manabe and O. Wada, J. Toxic. Sci. 6, 236 (1981)]. The aim of the present investigation was to test the effects in vitro of TPTF on platelet aggregation and to elucidate the mechanism of the inhibitory action by studying the release and metabolism of arachidonic acid and the cyclic AMP contents of rabbit platelets treated in vitro with TPTF. Although no inhibitory effect of TPTF was found on sodium arachidonate-induced platelet aggregation and ATP secretion, TPTF inhibited both reactions induced by collagen. Triphenylarsine and triphenylantimony did not inhibit, even at a concentration of 10(-3) M. The anti-aggregating concentration (IC50) of TPTF was 6.0 x 10(-6) M against collagen. TPTF had no inhibitory effect on the conversion of exogenous arachidonic acid to malondialdehyde (MDA) by platelets, while the collagen-induced production of arachidonate metabolites [MDA, 12-L-hydroxy-5,8,10-heptadecatrienoic acid (HHT) and thromboxane B2] was remarkably inhibited by TPTF. Furthermore, TPTF apparently inhibited the collagen-induced release of arachidonic acid from platelets, although the formation of phosphatidic acid was not inhibited. Total cyclic AMP content after TPTF exposure was not changed significantly. These results indicate that TPTF inhibited the collagen-induced arachidonic acid release from platelet phospholipids, presumably by acting on phospholipase A2. Furthermore, it seems unlikely that the inhibition of arachidonic acid release by TPTF can be explained by the level of cyclic AMP in platelets.

Adenosine Triphosphate↗
PubMed1985

Altered induction response of hepatic cytochrome P-450 to phenobarbital, 3-methylcholanthrene, and beta-naphthoflavone in organotin-treated animals.

The effects of tricyclohexyltin hydroxide on the induction of cytochrome P-450 in liver by phenobarbital, 3-methylcholanthrene and beta-naphthoflavone were studied. A single dose of the organotin (15 mg/kg body wt) prevented the full extent of phenobarbital induction of cytochrome P-450 from occurring; this was the case whether tricyclohexyltin was given 48 hr preceeding a single injection of phenobarbital, or administered simultaneously with the first of three daily doses of the drug. Elevation of hepatic heme oxygenase (EC 1.14.99.3) activity accompanied these changes in cytochrome P-450, but the induction of this enzyme was not affected by phenobarbital treatment. The induction of cytochrome P-448 by 3-methylcholanthrene and beta-naphthoflavone was not affected to the same extent by a single injection of tricyclohexyltin, while heme oxygenase induction was less pronounced when these cytochrome P-448 inducers were given together with the organotin. The changes in cytochrome P-450 content and in its functional activity resulting from the various treatments were further examined by sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis of the microsomal fractions. The electrophoretic profiles illustrate clearly that the apoprotein moieties of the various cytochrome P-450 subspecies are affected to a considerable extent by treatment with tricyclohexyltin hydroxide alone, and staining in these bands was noticeably reduced even when phenobarbital was administered together with the organotin. In contrast, tricyclohexyltin failed to decreased the 3-methylcholanthrene- or beta-naphthoflavone-induced cytochrome P-450 subspecies. These data suggest that significant metabolic interactions can occur from exposure to a combination of environmental chemicals and drugs resulting in an altered metabolism of heme and cytochrome P-450.

5-Aminolevulinate Synthetase↗
PubMed1995

Synthesis of 2- and 4-nitrophenyl beta-glycosides of beta-(1-->4)- D-xylo-oligosaccharides of dp 2-4.

2- and 4-Nitrophenyl beta-D-xylopyranosides (4 and 5) were transformed, via dibutyltin oxidemediated acylation, into the corresponding 2,3-di-O-benzoyl derivatives 11 and 15. Xylobiose and xylotriose were easily isolated by charcoal column chromatography from a commercially available material and converted into the di- and trisaccharide methyl 1-thio-beta-glycosides 36 and 37. The 2-and 4-nitrophenyl beta-glycosides of the beta-(1-->4)-D-xylo-oligosaccharides of dp 2-4 were synthesized by N-iodosuccinimide-silver triflate-promoted condensation using 11 and 15 as the glycosyl acceptors and ethyl 1-thio-beta-D-xylopyranoside triacetate 16, 36, and 37 as the glycosyl donors. Also described are an improved preparation of 4 and 5, and the synthesis of 1-naphthyl beta-D-xylopyranoside, as well as an alternative approach to the 2- and 4-nitrophenyl beta-xylobiosides.

Carbohydrate Sequence↗
PubMed1995

Synthesis of (1-->4)-beta-D-xylo-oligosaccharides of dp 4-10 by a blockwise approach.

Dibutyltin oxide-mediated regioselective chloroacetylation of methyl 1-thio-beta-xylobioside, followed by treatment of the product with 4-methylbenzoyl chloride-pyridine, gave methyl 4-O-chloroacetyl-2,3-di-O-(4-methylbenzoyl)-beta-D-xylopyranosyl-(1-->4) -2.3-di - O-(4-methylbenzoyl)-1-thio-beta-D-xylopyranoside (18) in 70% yield. Coupling of 18 with benzyl alcohol afforded the disaccharide benzyl beta-glycoside, which was O-dechloroacetylated to provide methyl 2,3-di-O-(4-methylbenzoyl)-beta-D-xylopyranosyl-(1-->4)-2,3-di-O-(4- methylbenzoyl)-1-thio-beta-D-xylopyranoside (20). A homologous series of (1-->4)-beta-D-xylo-oligosaccharides from the tetra- to the deca-saccharide have been synthesized in a blockwise manner by using 20 as the glycosyl acceptor, 18, methyl 1-thio-beta-xylobioside pentaacetate, and methyl 1-thio-beta-xylotrioside heptaacetate as the glycosyl donors, and a combination of N-iodosuccinimide-silver triflate as the promoter.

Carbohydrate Conformation↗
PubMed1990

Activation of a complex of ATPase with the natural protein inhibitor in submitochondrial particles.

Almost all ATPase molecules in submitochondrial particles, isolated from beef heart mitochondria in the presence of MgATP, are in an active complex with the natural protein inhibitor (IF1). In de-energized particles at high ionic strength a slow and irreversible ATPase activation is found to occur due to a dissociation of the enzyme-inhibitor complex. The pH-dependence of this process points out that deprotonation of IF1 molecule is an essential step in the dissociation of the complex. Zn2+ sharply accelerates ATPase activation, probably via binding with the deprotonated form of IF1. ATPase activation is completely prevented by MgATP, indicating the formation of a transient enzyme-inhibitor complex retaining ATPase activity.

Adenosine Triphosphatases↗
PubMed1991

The effect of F0 inhibitors on the Vibrio alginolyticus membrane ATPase.

The inhibition of membrane ATPase from the marine alkalotolerant bacterium Vibrio alginolyticus by DCCD, triphenyltin and venturicidin was studied. DCCD proved to be an irreversible inhibitor, while venturicidin and triphenyltin produced a reversible inhibitory effect. The DCCD-binding proteolipid was identified in the membrane preparations. The effect of the inhibitors on ATPase activity and ATP-dependent Na(+)-transport in V. alginolyticus subcellular vesicles is discussed.

Adenosine Triphosphate↗