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PubMed2004

Anomeric oxygen to carbon rearrangements of alkynyl tributylstannane derivatives of furanyl (gamma)- and pyranyl (delta)-lactols.

Tetrahydropyran and tetrahydrofuran containing natural products, drugs and agrochemicals often possess carbon-carbon bonds adjacent to the heteroatom. Consequently, new methods for the construction of anomeric carbon-carbon bonds are of considerable importance. We have devised a new strategy to access these systems that requires the treatment of O-glycoside alkynyl tributylstannane derivatives of furanyl and pyranyl lactols with Lewis acid to effect oxygen to carbon rearrangements. This leads to the formation of the corresponding carbon linked alkynol products that can be further manipulated to produce key structural motifs and building blocks for the assembly of complex molecules.

Alkynes↗
PubMed2004

Intramolecular nucleophilic carbonyl trapping of alpha-ketenyl radicals by an amino group.

Free-radical carbonylation of omega-alkynylamines with tributyltin hydride gives a mixture of alpha-methylene lactams and alpha-stannylmethylene lactams. Nucleophilic addition of an internal amino group to the carbonyl group of alpha-ketenyl radicals is proposed as the cyclization step. The subsequent unusual 1,4-H shift from the resulting 1-hydroxyallyl radical, followed by elimination of the beta-tributyltin radical leads to the formation of alpha-methylene lactams.

Amines↗
PubMed2006

Antifouling strategies for marine and riverine sensors.

Traditionally, water quality has been monitored by sampling and lab based analysis. However, there are disadvantages associated with this method, for example, deterioration of samples with time, limited sampling points, limited temporal monitoring. This has provided impetus for the development of sensors which can be deployed from remote locations over extended deployment periods. However, a major limitation of these systems is their vulnerability to biofouling. This review outlines the research that has been carried out on strategies for the protection of marine and riverine sensors against fouling.

Animals↗
PubMed1975

The action of tributyltin on energy coupling in coupling-factor-deficient submitochondrial particles.

1. Tributyltin at concentrations of approx. 1nmol/mg of protein induces respiratory control and lessens the protein permeability of coupling-factor-deficient submitochondrial particles. 2. At these concentrations or lower, it increases the P/O ratio of the particles to a small extent and inhibits the adenosine triphosphatase activity without greatly increasing its sensitivity to uncoupling agents. 3. It fails to stimulate ATP-driven reversed electron transport or transhydrogenase, but stimulates the transhydrogenase driven by aerobic succinate oxidation. 4. The results indicate that, unlike oligomycin, tributyltin does not discriminate between damaged and intact ATP-synthesizing complexes. 5. The relationship between the oligomycin- and tributyltin-binding sites is discussed.

Adenosine Triphosphatases↗
PubMed1976

The influence of adenine nucleotides and oxidizable substrates on triethyltin-mediated chloride uptake by rat liver mitochondria in potassium chloride media.

In a 100 mM-KCl medium, pH 6.8, containing ATP increasing concentrations of triethyltin cause an uptake of Cl- into mitochondria with a maximum at 1 muM. This can be inhibited by atractylate or oligomycin, but is virtually unaffected by the presence of rotenone. When the medium contains substrate (pyruvate, beta-hydroxybutyrate or succinate), both in the presence and absence of adenine nucleotides, Cl- uptake is greater with a maximum at 1-10 muM-triethyltin. If substrate oxidation is blocked by respiratory-chain inhibitors the Cl- uptake mediated by triethyltin is inhibited except in the media containing ATP, when the characteristics of Cl- uptake similar to that found in the medium containing ATP alone are observed. Under all conditions tested Cl- uptake is decreased by the presence of 2,4-dinitrophenol. It is concluded that energy from either the oxidation of substrate or the hydrolysis of ATP is associated with the generation of sufficient OH- to enable the triethyltin-mediated Cl-/OH- exchange to occur under the metabolic conditions relevant to this action of triethyltin.

Adenosine Triphosphate↗
PubMed1977

Studies of energy-linked reactions. Localization of the site of action of trialkyltin in yeast mitochondria.

Ligand-binding studies with labelled triethyltin on yeast mitochondrial membranes showed the presence of high-affinity sites (KD = 0.6 micronM; 1.2 +/- 0.3 nmol/mg of protein) and low-affinity sites (KD less than 45 micronM; 70 +/- 20 nmol/mg of protein). The dissociation constant of the high-affinity site is in good agreement with the concentration of triethyltin required for inhibition of mitochondrial ATPase (adenosine triphosphatase) and oxidative phosphorylation. The high-affinity site is not competed for by oligomycin or venturicidin, indicating that triethyltin reacts at a different site from these inhibitors of oxidative phosphorylation. Fractionation of the mitochondrial membrane shows a specific association of the high-affinity sites with the ATP synthase complex. During purification of ATP synthase (oligomycin-sensitive ATPase) there is a 5-6-fold purification of oligomycin- and triethyltin-sensitive ATPase activity concomitant with a 7-9-fold increase in high-affinity triethyltin-binding sites. The purified yeast oligomycin-sensitive ATPase complex contains approximately six binding sites for triethyltin/mol of enzyme complex. It is concluded that specific triethyltin-binding sites are components of the ATP synthase complex, which accounts for the specific inhibition of ATPase and oxidative phosphorylation by triethyltin.

Adenosine Triphosphatases↗
PubMed1977

Mitochondrial adenosine triphosphatase of the fission yeast Schizosaccharomyces pombe 972h-. Changes in inhibitor sensitivities during the cell cycle indicate similarities and differences in binding sites.

1. We used 11 different inhibitors of energy conservation as inhibitors of ATPase (adenosine triphosphatase) in extracts of Schizosaccharomyces pombe obtained from cells at different stages of the cell cycle. 2. All the inhibitors showed cell-cycle-dependent variations in their I50 values (microng of inhibitor/mg of protein giving 50% inhibition of inhibitor-sensitive ATPase at pH 8.6). 3. From the sensitivity profiles through the cell cycle it was concluded that: (a) oligomycin, venturicidin, triethyltin sulphate and dibutylchloromethyltin chloride all act at closely associated site(s); (b) NN'-dicyclohexylcarbodi-imide and leucinostatin both act at a similar site, which is, however, distinct from that at which other inhibitors of the membrane factor (Fo) act. 4. The variations in I50 values for efrapeptin closely followed changes in specific activity of ATPase, as would be expected for an inhibitor acting at catalytic sites; these fluctuations were different from those for aurovertin, Dio-9, 4-chloro-7-nitrobenzofurazan, quercetin and spegazzinine, all of which show different sensitivity profiles from one another. 5. Anomalous stepwise inhibitor-titration curves were obtained for spegazzinine, NN'-dicyclohexylcarbodiimide, dibutylchloromethyltin chloride and leucinostatin. 6. Possible explanations are proposed for the discontinuous expression of inhibitor-binding sites during the cell cycle.

Adenosine Triphosphatases↗
PubMed1977

Dibutylchloromethyltin chloride, a covalent inhibitor of the adenosine triphosphate synthase complex.

1. The synthesis of dibutylchloromethyltin chloride, a new covalent inhibitor of the mitochondrial ATP synthase [oligomycin-sensitive ATPase (adenosine triphosphatase)] complex is described, together with a method for preparing dibutylchloro[(3)H]methyltin chloride. 2. Studies with the yeast mitochondrial oligomycin-sensitive ATPase complex show that dibutylchloromethyltin chloride inhibits both the membrane-bound enzyme and also the purified Triton X-100-dispersed preparation. 3. F(1)-ATPase is not inhibited even at 500nmol of dibutylchloromethyltin chloride/mg of protein, and the general inhibitory properties are similar to those of triethyltin, oligomycin and dicyclohexylcarbodi-imide, known energy-transfer inhibitors of oxidative phosphorylation. 4. Binding studies with yeast submitochondrial particles show that dibutylchloromethyltin chloride antagonizes the binding of triethyl[(113)Sn]tin, indicating that there is an interaction between the two inhibitor-binding sites. 5. Unlike triethyltin, inhibition by dibutylchloromethyltin chloride is due to a covalent interaction which titrates a component of the inner mitochondrial membrane present at a concentration of 8-9nmol/mg of protein. 6. All of the labelled component can be extracted with chloroform/methanol (2:1, v/v), and sodium dodecyl sulphate/polyacrylamide-gel electrophoresis of the chloroform/methanol extract indicates that the labelled component has an apparent mol.wt. of 6000-8000. However, t.l.c. reveals the presence of only one labelled component which is lipophilic and non-protein and is distinct from the free inhibitor, mitochondrial phospholipids and the dicyclohexylcarbodi-imide-binding protein (subunit 9). 7. Inhibition of mitochondrial ATPase and oxidative phosphorylation is correlated with specific interaction with a non-protein lipophilic component of the mitochondrial inner membrane which is proposed to be a co-factor or intermediate of oxidative phosphorylation.

Adenosine Triphosphatases↗
PubMed1978

Properties of energy-dependent calcium transport by rat liver microsomal fraction as revealed by initial-rate measurements.

Measurements of the initial rate of Ca2+ transport by rat liver microsomal preparations reveal the existence of two phases of transport activity. The first, a phase of rapid transport, is complete by 3-5 min, at which time the second (slower) phase begins; this remains linear for up to at least 40 min. The initial phase is minimal in the absence of MgATP. The initial rate of Ca2+ transport reaches values as high as 25 nmol/min per mg of protein; the Km for Ca2+total is 1-2 micrometer and that for MgATPtotal about 500 micrometer. Ruthenium Red (3-5 nmol/mg of protein) has little effect on the initial rate of transport, whereas tributylin (2 micrometer) inhibits equally in a KC1- or a KNO3-containing medium. Compunds that collapse components of the proton electrochemical gradient in mitochondria (valinomycin and carbonyl cyanide m-chlorophenylhydrazone) each inhibit by 70-80% the initial rate of microsomal Ca2+ transport.

Adenosine Triphosphate↗
PubMed1978

Inability of tributyltin-induced chloride/hydroxyl exchange to stimulate calcium transport in mitochondria isolated from flight muscle of the sheep blowfly Lucilia cuprina.

Tributyltin in the concentration range 1-4mum failed to stimulate Ca(2+) transport by Lucilia flight-muscle mitochondria in a medium containing KCl and respiratory substrate but devoid of P(i), despite its promotion of a rapid Cl(-)/OH(-) exchange. When 2mm-P(i) was present, concentrations of tributyltin greater than 1mum inhibited the initial rate of Ca(2+) transport and induced efflux of the ion from the mitochondria in Cl(-)- or NO(3) (-)-containing media. Lower concentrations had little effect. Oligomycin added at up to 10mug/mg of mitochondrial protein had no effect on Ca(2+) transport. By contrast, approx. 0.3mum-tributyltin completely inhibited respiration supported by alpha-glycerophosphate in either the presence or absence of added ADP. The data suggest that tributyltin can inhibit Ca(2+) transport in Lucilia flight-muscle mitochondria other than by facilitating a Cl(-)/OH(-) exchange or producing an oligomycin-like effect.

Animals↗
PubMed1986

Organotin-protein interactions. Binding of triethyltin bromide to cat haemoglobin.

Triethyltin binds to native cat and rat haemoglobin but not to their denatured forms or to other animal haemoglobins. Two molecules of the organotin bind to one molecule of R-state cat haemoglobin with affinity constants of about 1 X 10(5) M-1. Little or no triethyltin is bound to the deoxygenated (T-state) protein. Binding appears to be dependent upon the existence of a specific three-dimensional configuration of cysteine and histidine residues. The properties of the triethyltin-cat haemoglobin complex are consistent with those of a haemoglobin conformer whose allosteric equilibrium is displaced toward the R-state. Its oxygen affinity and rate of oxidation by nitrite is increased, and the rate of reduction of the methaemoglobin derivative by ascorbate is decreased. These effects of triethyltin are opposite and antagonistic to the effects of inositol hexaphosphate. They are exerted on the alpha- as well as beta-haem groups, even though triethyltin is bound at sites on alpha-globin far removed from the haem groups.

Animals↗
PubMed1988

Activation and inhibition of microsomal glutathione transferase from mouse liver.

Mouse liver microsomal glutathione transferase was purified in an N-ethylmaleimide-activated as well as an unactivated form. The enzyme had a molecular mass of 17 kDa and a pI of 8.8. It showed cross-reactivity with antibodies raised against rat liver microsomal glutathione transferase, but not with any of the available antisera raised against cytosolic glutathione transferases. The fully N-ethylmaleimide-activated enzyme could be further activated 1.5-fold by inclusion of 1 microM-bromosulphophthalein in the assay system. The latter effect was reversible, which was not the case for the N-ethylmaleimide activation. At 20 microM-bromosulphophthalein the activated microsomal glutathione transferase was strongly inhibited, while the unactivated form was activated 2.5-fold. Inhibitors of the microsomal glutathione transferase from mouse liver showed either about the same I50 values for the activated and the unactivated form of the enzyme, or significantly lower I50 values for the activated form compared with the unactivated form. The low I50 values and the steep slope of the activity-versus-inhibitor-concentration curves for the latter group of inhibitors tested on the activated enzyme indicate a co-operative effect involving conversion of activated enzyme into the unactivated form, as well as conventional inhibition of the enzyme.

Animals↗
PubMed1992

Design of two chimaeric human-rat class alpha glutathione transferases for probing the contribution of C-terminal segments of protein structure to the catalytic properties.

Two chimaeric human-rat class Alpha glutathione transferases were constructed by fusion of DNA segments derived from the plasmids pTGT2-AT and pGTB38 and expression of the corresponding proteins in Escherichia coli. The recombinant proteins H1R1/1 and H1R1/2 encoded by plasmids pH1R1/1 and pH1R1/2 are composed of a segment of the human class Alpha subunit 1 from the N-terminus to His-143 and Pro-207 respectively, followed by the complementary C-terminal portion of the rat class Alpha subunit 1 sequence. Compared with the parental human enzyme, H1R1/1 is altered in 20 positions due to the introduction of 79 residues from the rat enzyme, while H1R1/2 is altered in five positions out of 15 in the C-terminal region. The design of mutant H1R1/1 is equivalent to introduction of exons 6 and 7 of the rat subunit 1 gene in place of the homologous human nucleotide sequence. The two chimaeric proteins are enzymatically active with several substrates, even though the activity in most cases is somewhat decreased in comparison with the wild-type human enzyme. Inhibition studies show that the kinetic properties mimic those of the human enzyme, indicating that the N-terminal two-thirds of the primary structure plays the major role in governing the catalytic properties. The results of this study demonstrate that recombination of segments of primary structure between homologous enzymes may serve as a useful cassette technique for design of novel catalytically active proteins.

Amino Acid Sequence↗
PubMed1993

Differential control of free calcium and free zinc levels in isolated bovine liver nuclei.

Modulation of intracellular signal transduction by Ca2+ and possibly Zn2+ is based on an effective homoeostatic control of the corresponding free ion concentrations. We used the fluorescent indicator fura-2 to monitor concentrations of free Ca2+ and free Zn2+ in nuclei isolated from bovine liver. The nuclei showed an ATP-stimulated accumulation of intranuclear free Ca2+, which was inhibited in the presence of the Ca(2+)-pump inhibitor thapsigargin. Furthermore, uptake and intranuclear levels of free Zn2+ were measured after incubation with different extranuclear Zn2+ concentrations. There was no stimulating effect of ATP on Zn2+ uptake. Our data suggest that the levels of intranuclear free Ca2+ and free Zn2+ are controlled differentially. A distinct regulation of free ion levels in the nucleus may contribute to the specific control of nuclear events associated with gene transcription and cell differentiation.

Adenosine Triphosphate↗
PubMed2003

T-cell activation and the development of an apoptosis-resistant CD45RO+ T-cell population.

Growing experimental evidence supports a broadening role for the caspases; not only do they participate in the process of apoptosis but also in the control of the cell cycle and cellular proliferation. The biological role of the caspases in the process of T-cell activation and proliferation is still not defined. In the present study, we propose a potential role, by demonstrating an association of T-cell receptor-mediated caspase activity with the development of an apoptosis-resistant memory CD45RO+ T-cell population. As previously shown by us, a time-dependent induction of caspase activity, in the absence of apoptosis, can be observed in CD3-stimulated human peripheral blood lymphocytes. We here show that a population of CD45RO+ cells, with activated caspase-3 and with resistance to tributyltin-induced apoptosis, develops after 3 days of stimulation. A concomitant expression of the anti-apoptotic protein Bcl-xL accompanied the caspase activity and the development of the apoptosis-resistant phenotype. Finally, upon co-culturing with dexamethasone (DEX), the CD3-induced caspase-3 activity was blocked. During this condition, the expression of the activation marker HLA-DR as well as the cellular proliferative response was strongly suppressed. The development of memory cells with a CD45RO+ phenotype was also blocked. Our data support the hypothesis that caspase-3 activity, observed in CD3-stimulated cells, may be an important component in the proliferation process and, furthermore, might play a role for the development of memory T cells, and DEX inhibits this process.

Apoptosis↗
PubMed1999

Interactions of fluorescent triacylglycerol analogs covalently bound to the active site of a lipase from Rhizopus oryzae.

Fluorescent triacylglycerol analogs were synthesized as covalent inhibitors of lipase activity. The respective 1(3), 2-O-dialkylglycero-3(1)-alkyl-phosphonic acid p-nitrophenyl esters contain a fluorescent pyrenealkyl chain and a long-chain alkyl residue bound to the sn-2 and sn-1(3) positions of glycerol, respectively. The phosphonic acid p-nitrophenyl ester bond is susceptible to nucleophilic substitution by the active serine residue in the catalytic triad of a lipase, leading to inactivation of the enzyme. The fluorescent dialkylglycerophosphonates contain two chiral centers, the sn-2 carbon of glycerol and the phosphorus atom. The (1-O-hexadecyl-2-O-pyrenedecyl-sn-glycero)-O-(p-nitrophenyl)-n-hex yl- phosphonate, first peak during HPLC separation and the (3-O-hexadecyl-2-O-pyrenedecyl-sn-glycero)-O-(p-nitrophenyl)-n-hex yl- phosphonate, second peak during HPLC separation were found to be potent lipase inhibitors. After incubation of an equimolar amount of these isomers with lipase from Rhizopus oryzae complete inactivation was observed. Stable conjugates containing a 1 : 1 molar ratio of lipid to protein were formed. The spatial proximity of the fluorescently labeled sn-2 alkyl chain of the inhibitor and tryptophan residues of the lipase was assessed by fluorescence resonance energy transfer. The extent of tryptophan fluorescence quenching and the concomitant increase in pyrene fluorescence upon excitation of lipase tryptophans was found to be similar for the above-mentioned isomers. Thus, the (labeled) sn-2 alkyl chains of a triacylglycerol analog are likely to interact with the same binding site of the R. oryzae lipase, irrespective of their steric configuration. However, it was shown that the extent of resonance energy transfer is strongly influenced by the reaction medium, indicating conformational changes of the lipase in different environments.

Binding Sites↗
PubMed2003

Tributyltin and copper effects on encystment and in vitro excystment of Parorchis acanthus larvae.

Effects of tributyltin (TBT) and copper (Cu) on cercariae and metacercariae of the trematode Parorchis acanthus (Digenea: Philophthalmidae) were investigated. Cercariae released by the dogwhelk, Nucella lapillus were maintained in natural seawater (SW) or solutions of TBT or Cu ranging from 0.001-100 microg l(-1) and 1-6 mg l(-1) respectively before they encysted. Over 79% of the cercariae encysted in control and test solutions. Low concentrations of TBT reduced encystment success more than low concentrations of Cu. The percentage of cercariae that formed cysts in the highest concentrations of both pollutants was higher than in the controls, perhaps representing an 'emergency response' to the pollutants. Before being induced to excyst in vitro, metacercariae were left in the heavy metal solutions for 3 weeks. Metacercariae exposed as cercariae to TBT and Cu achieved lower percentage excystment success than those that had encysted in SW. Cyst walls provided greater protection against Cu than TBT. It was concluded that TBT and Cu had a detrimental effect on the larval stages of P. acanthus at the higher concentrations used but the cyst wall afforded an element of protection if formed in unpolluted seawater before the larval stages were subjected to the pollutants.

Animals↗