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Biomedical subjects

E Tipping

Publications and source records attributed to E Tipping.

At least 37 records · Page 2Linked to original sources
PubMed1989

Adsorption of aluminium by stream particulates.

An experimental study was made of the adsorption of aluminium by fine particulates from Whitray Beck, a hill stream in NW England. Adsorption increased with Al(3) activity, pH and concentration of particles, and could be quantitatively described by the empirical equation: [Formula: see text] [particles] where square brackets indicate concentrations, curly brackets, activities, and alpha, beta and gamma are constants with values of 5.14x10(-10) (mol litre(-1))(2.015) (g particles litre(-1))(-1), 0.457, and 1.472, respectively. For the experimental data, the equation gave a correlation ratio of 0.99. The equation accounts reasonably well for the adsorption of Al by particulates from seven other streams. In applying the equation, it must be borne in mind that the desorption kinetics of Al depend on pH, and rapid reversibility (<15min) can only be assumed for pH or=10%) of total monomeric Al.

Journal Article↗
PubMed1989

Reclamation of acid waters using sewage sludge.

An exhausted sand quarry which had filled with acid water (pH 3) from the oxidation of pyrite was treated with calcium hydroxide to neutralize the water (pH 8), and sewage sludge to prevent further ingress of acid. The water remained neutral for 2 years, an appreciable quantity of base being generated by the reduction of sulphate to sulphide in the anoxic sediment formed by the sewage sludge. After this time the water reverted to acid conditions, chiefly because the lake was too shallow to retain the sewage sludge over a sufficiently large area of its bed. Incubation experiments showed that the sewage sludge had a large capacity for sulphate reduction, which was equally efficient in acid or neutral waters and that the areal rate of consumption was sufficiently fast to neutralize all incoming acid, if at least 50% of the lake bed was covered with sludge. Throughout the course of the field investigations there was no foul smell and the lake was quickly colonized by phytoplankton, macrophytes and insects. Although nutrients associated with the sewage sludge stimulated photosynthesis and so caused the generation of additional organic matter, they were exhausted within two years. To ensure permanent reclamation, phosphate fertilizer could be added once the initial supply has been consumed. Neutralization removed trace metals from the system, presumably due to formation of insoluble oxyhydroxide and carbonates. The solubility of aluminium was apparently controlled by a basic aluminium sulphate (jurbanite).

Journal Article↗
PubMed1989

Acid-sensitive waters of the English Lake District: a steady-state model of streamwater chemistry in the upper Duddon catchment.

Data on deposition and streamwater chemistry, obtained for the upper catchment of the River Duddon in the 1970s and 1980s, are reviewed. These data, together with soil chemical data, are used to deduce key processes in the deposition-catchment interaction, the analysis being based on current concepts of acidification. The processes are incorporated into a steady-state model that allows streamwater compositions to be calculated. The large baseflow pH range (5-7) of Duddon streams is accounted for in the model by a range of base cation weathering rates. Other processes invoked are evapotranspiration, the uptake of nitrogen by plants, dissolution of Al(OH)(3) in the mineral soil, precipitation of Al(OH)(3) in the baserock zone and in streamwater, Al(3+) hydrolysis, and reactions of the carbonate system. Both cation exchange and sulphate adsorption are ignored, because they are assumed to influence rates-of-change between steady states, but not steady-state water compositions per se. The model can be used to estimate variations in streamwater composition with flow. Model calculations suggest that a 50% decrease in depositional acidifying components (sulphur oxides and NH(4)(+)) would result in increases of up to 1 pH unit in streamwaters with present-day baseflow pH values of 5 or less. It appears that water quality in the upper Duddon is currently more sensitive to inputs of NH(4)(+) than of H(2)SO(4). To improve the reliability of model predictions, more information is required on (a) the pH dependence of base cation weathering, (b) transformations involving nitrogen, (c) aluminium chemistry and (d) partial pressures of CO(2) in soil and baserock.

Journal Article↗
PubMed1981

The influence of soluble binding proteins on lipophile transport and metabolism in hepatocytes.

A theory is presented that deals with the involvement of the intracellular binding proteins ligandin and aminoazodye-binding protein A (otherwise known as Z-protein or fatty-acid-binding protein) on the uptake and intracellular transport and metabolism of their ligands. Equations are derived that combine steady-state diffusional fluxes of small molecules that are (a) free in the aqueous phase of the cell, (b) bound to the two proteins and (c) partitioned into intracellular membranes, for model systems that resemble conditions in the rat hepatocyte. These equations are then combined with expressions for the enzyme-catalysed metabolic reactions undergone by these small molecules to assess the influence of diffusion rats on the overall metabolic rates. It is concluded that ligandin and protein A can enhance the rate of intracellular of their ligands by an order of magnitude or more and that this could make the hepatocyte several times more efficient in metabolizing these ligands. Various ways of testing this theory are discussed.

Animals↗
PubMed1980

The non-covalent binding of benzo[a]pyrene and its hydroxylated metabolites to intracellular proteins and lipid bilayers.

The non-covalent interactions of benzo[a]pyrene (BP) and several of its hydroxylated metabolites with ligandin, aminoazodye-binding protein A (Z-protein, fatty acid binding protein) and lecithin bilayers have been studied by equilibrium dialysis, an adsorption technique and fluorescence spectroscopy. Binding affinities expressed as v/c (where v = moles of BP or BP metabolite bound per mole of protein or lipid and c = unbound concentration), were measured at concentrations sufficiently low that there was no self-association of the unbound compounds as judged by their fluorescence characteristics. 3-Hydroxybenzo[a]pyrene (BP-3-phenol), 4,5-dihydro-4,5-dihydroxybenzo[a]pyrene (BP-4,5-dihydrodiol) and 7,8-dihydro-7,8-dihydroxybenzo[a]pyrene (BP-7,8-dihydrodiol) bind more strongly (v/c = 10(5)-5 x 10(5) l x mol-1) to all three binders than does BP itself (v/c = 10(4)-7 x 10(4) l x mol-1). 9,10-Dihydro-9,10-dihydroxybenzo[a]pyrene (BP-9,10-dihydrodiol) binds to ligandin with an affinity similar to those of the other BP metabolites studied here, but binds much less strongly to both protein A and lecithin (v/c = 10(4) and 3 x 10(4) x mol-1, respectively). The low affinity of BP-9,10-dihydrodiol for lecithin would account for earlier findings that on incubation of BP with isolated rat hepatocytes, this metabolite egressed from the cells to the extracellular medium much more readily than either BP-4,5-dihydrodiol or BP-7,8-dihydrodiol. Calculations based on these results suggest that within hepatocytes BP and its metabolites, including BP-9,10-dihydrodiol, will be found almost exclusively associated (> 98%) with lipid membranes.

Adsorption↗
PubMed1979

Interactions of small molecules with phospholipid bilayers. Binding to egg phosphatidylcholine of some uncharged molecules (2-acetylaminofluorene, 4-dimethylaminoazobenzene, oestrone and testosterone) that bind to ligandin and aminoazo-dye-binding protein A.

1. To assess the possible involvement of ligandin and aminoazo-dye-binding protein A in intracellular transport it is necessary to know how their ligands, most of which are molecules with hydrophobic moieties, interact with cellular membranes. To obtain such information we have examined the interactions of 2-acetylaminofluorene, 4-dimethylaminoazobenzene, oestrone and testosterone with aqueous dispersions of egg phosphatidylcholine and egg phosphatidylcholine/cholesterol (1:1, molar ratio) by equilibrium dialysis and spectrophotometry. 2. At 25 degrees C and pH7.4, the partition coefficients for binding to phosphatidylcholine [expressed as (mol of ligand bound/mol of phosphatidylcholine)/unbound ligand concentration] were: for 2-acetylaminofluorene, 5.0x10(3) litre.mol(-1); for 4-dimethylaminoazobenzene, 2.1x10(4) litre.mol(-1); for oestrone, 3.1x10(3) litre.mol(-1); and for testosterone, 4.2x10(2) litre.mol(-1). In the ranges studied these values were independent of concentration. The results for the two steroids confirm those of Heap, Symons & Watkins [(1970) Biochim. Biophys. Acta218, 482-495]. 3. The introduction of cholesterol into the lipid bilayers caused large decreases in the partition coefficients of oestrone and testosterone, but had relatively little effect on the binding of 2-acetylaminofluorene and 4-dimethylaminoazobenzene. 4. By assuming that the interactions with egg phosphatidylcholine bilayers resemble those with the phospholipid components of mammalian intracellular membranes the phosphatidylcholine partition coefficients, together with data for binding to the intracellular proteins ligandin and aminoazo-dye-binding protein A, enable the subcellular distributions of the four compounds to be estimated. For the rat hepatocyte up to 98, 99, 89 and 58% of the total 2-acetylaminofluorene, 4-dimethylaminoazobenzene, oestrone and testosterone respectively may be membrane-bound.

2-Acetylaminofluorene↗
PubMed1979

Interactions of small molecules with phospholipid bilayers. Binding to egg phosphatidylcholine of some organic anions (bromosulphophthalein, oestrone sulphate, haem and bilirubin) that bind to ligandin and aminoazo-dye-binding protein A.

1. To assess the possible involvement of ligandin and aminoazo-dye-binding protein A in intracellular transport it is necessary to know how their ligands, most of which are molecules with hydrophobic moieties, interact with cellular membranes. To obtain such information we examined the interactions of bromosulphophthalein, oestrone sulphate, haem and bilirubin with aqueous dispersions of egg phosphatidylcholine and egg phosphatidylchone/cholesterol (1:1, molar ratio) by equilibrium dialysis and spectrophotometry. 2. In all four cases, saturation effects were observed. Values of Vmax (v = mol of compound bound/mol of lipid phosphorus) at 25 degrees C were: for bromosulphophthalein, approximately 0.1; for oestrone sulphate, approximately 0.25; for haem, approximately 0.25 (all at pH 7.4); and for bilirubin 0.1--0.2 (at pH 8.2). 3. Limiting values of v/c (c = unbound concentration) as v leads to 0 at 25 degrees C and pH 7.4 are: for bromosulphophthalein, 6.25 x 10(4) litre-mol-1; for oestrone sulphate, 7.8 x 10(2) litre-mol-1; for haem, 4.5 x 10(5) litre-mol-1; and for bilirubin, approximately 1.2 x 10(4) litre-mol-1. For haem the result depends on the assumption that only the monomeric form binds to the lipid. 4. The binding of each compound was decreased by cholesterol; bromosulphophthalein and oestrone sulphate were affected more than haem and bilirubin. 5. Bromosulphophthalein at saturating concentration decreased the limiting values of v/c of the other three compounds by approximately one order of magnitude. 6. By assuming that the interactions with egg phosphatidylcholine resemble those with the phospholipid components of mammalian intracellular membranes the binding data for phosphyatidylcholine, together with data for binding to the intracellular proteins ligandin and aminoazo-dye-binding protein A, enable the subcellular distributions of the four compounds to be estimated. For the rat hepatocyte up to 92, 51, 98 and 47% of the total bromosulphophthalein, oestrone sulphate, haem and bilirubin respectively may be membrane-bound.

Bilirubin↗
PubMed1979

The binding and catalytic activities of forms of ligandin after modification of its thiol groups.

Ligandin (glutathione S-transferase B, EC 2.5.1.18)was treated with p-mercuribenzoate, N-(4-dimethylamino-3,5-dinitrophenyl)-maleimide, 5,5,-dithiobis-(2-nitrobenzoic acid), N-ethylmaleimide, iodoacetamide or iodoacetate. Although performic acid oxidation revealed the presence of four cysteines, p-mercuribenzoate and N-(4-dimethylamino-3,5-dinitrophenyl)maleimide, the most effective of the reagents studied, reacted with only three residues. N-Ethylmaleimide and 5,5'-dithiobis-(2-nitrobenzoic acid) each reacted with two cysteines: iodoacetamide reacted with only one cysteine and iodoacetate was essentially unreactive. Modification of three thiol groups decreased both the enzymic and binding activities of ligandin although the number of binding sites was unaffected. Modification of only one or two of the thiol groups had little effect on the ligandin activities. It therefore appears that there is a thiol group in the common hydrophobic-ligand- and substrate-binding site of ligandin. Ligandin was separated into two fractions on CM-cellulose. Both fractions gave the same results with p-mercuribenzoate and iodoacetamide.

Binding Sites↗
PubMed1979

The interactions of triethyltin with rat glutathione-S-transferases A, B and C. Enzyme-inhibition and equilibrium-dialysis studies.

Purified glutathione(GSH)-S-transferases A, B and C from rat liver are inhibited by triethyltin (SnEt3). With 1-chloro-2,4-dinitro benzene (CDNB) as the limiting substrate the inhibition is competitive in each case. At a GSH concentration of 5 . 10(-3) M the inhibition constants for transferases A and C at 25 degrees C are similar and very low, 3.2 . 10(-8) M and 5.6 . 10(-8) M respectively, whereas for transferase B the inhibition constant is 3.5 . 10(-5) M. Equilibrium-dialysis experiments carried out at 4 degrees C in the absence of GSH give apparent dissociation constants of 7.1 . 10(-4) M and 3.4 . 10(-4) M for transferases A and B respectively, but if 5 . 10(-3) M glutathione is included in the dialysis solutions these values fall to 2.0 . 10(-7) M and 2.6 . 10(-5) M, which are within an order of magnitude of the kinetic Ki-values. Chromatographic experiments with Sephadex G-10 show that GSH and SnEt3 interact in aqueous solution under the conditions of the enzyme-kinetic and equilibrium-dialysis experiments. It is suggested that the inhibited enzymes are in the form of ternary complexes, enzyme-GSH-SnEt3, in which GSH and SnEt3 may or may not interact directly; or are possibly quaternary complexes, enzyme-(GSH)2-SnEt3. SnEt3 could be valuable as a selective inhibitor of transferases A and C in mixtures of the three transferases.

Animals↗
PubMed1978

The binding of porphyrins by ligandin.

Spectrophotometric and equilibrium-dialysis measurements show that ligandin (glutathione S-transferase B, EC 2.5.1.18) binds monomeric porphyrins at a single site with association constants in the range 10(4)-10(6) litre/mol at pH 7.0. Binding affinities are paralleled by the tendencies of the porphyrins to aggregate, increasing in the order: uroporphyrins I and III less than coproporphyrins I and III approximately haematoporphyrin less than protoporphyrin IX. From this it is deduced that the hydrophobic effect is the predominant driving-force for binding. The porphyrins can be displaced from their binding site on ligandin by bromosulphophthalein and oestrone sulphate. In enzyme inhibition studies, 50% inhibition was brought about by 8 micron-haematoporphyrin and by 1 micron-protoporphyrin IX. In the analysis of the haemotoporphyrin-ligandin system the self-association of haematoporphyrin was studied in detail. It was found to be limited to dimerization in the concentration range 0-200 micron at pH 7.0, 25 degrees C and a dimerization constant of 1.9 x 10(5) litre/mol was determined. Coproporphrin III has a dimerization constant of 5.2 x 10(5) litre/mol under the same conditions.

Coproporphyrins↗
PubMed1976

The non-convalent binding of small molecules by ligandin. Interactions with steroids and their conjugates, fatty acids, bromosulphophthalein carcinogens, glutathione and realted compounds.

1. Equilibrium dialysis studies have been made of the binding of a number of small molecules by rat ligandin. Direct measurements of binding together with competition experiments indicated that bromosulphophthalein, oestrone sulphate and dehydroepiandrosterone sulphate each bind at the same single primary binding site with association constants of 1.1 X 10(7), 6.6 X 10(5) and 2.6 X 10(5) 1/mol respectively at pH 7.0,IO.16M,4 degrees C. As well as bromosulphophthalein and dehydroepiandrosterone sulphate, a number of strucurally similar organic anions including 2-hydroxyoestradiol-glutathione oestrone glycyronide, N-methyl-4-aminoazobenzene-glutathione and several bile acids, were able to displace oestrone sulphate from ligandin in a manner consistent with competition at a single binding site. From these experiments association constants for the competing ligands were derived; these were inthe range 1 X 10(4)-1 X 10(6) 1/mol. 2. Ligandin was found to bind a number of compounds for which, because of their low aqueous solubilities relative to their binding affinities complete binding isotherms could bot be obtained. These included several steroids (but not cortisol), 20-methylcholanthrene, diethylstilboestrol, oleate and palmitate. Oestrone sulphate was able to compete with these ligands for binding and the results of the competition experiments were interpretable in terms of 1:1 competition at a single binding site. 3. In general the conjugation of non-polar ligands with sulphate or glutathione resulted in increased affinities, but such increases were relatively small (approximately 15% in therms of free energy) implying that the main driving force for the binding of both the conjugated and unconjugated species was the hydrophobic effect. This conclusion is borne out by the observations that both oestrone and its sulphate showed slight increases in affinity with increase in ionic strength, as would be expected for hydrophobic interactions. 4. As well as non-polar compounds and organic anions, ligandin was also found to bind sulphate and glucuronate to a measurable degree, and to interact quite strongly with glutathione. For the latter compound a single binding site was found with an association constant of 1 X 10(5) 1/mol. Glutathione was able to cause the dissociation of the ligandin-oestrone sulphate complex, but this effect was not explicable in terms of simple 1:1 competition. 5. Both oestrone and oestrone sulphare were bound most strongly at pH 6-7, the affinity of the protein for these ligands falling off quite sharply on either side of this maximum. 6. The affinities of ligandin for bromosulphophthalein, steroids and their conjugates, diethylstilboestrol and N,N-dimethyl-4-aminoazobenzene are similar in magnitude to those of serum albumin and aminoazodye-binding protein A (B. Ketterer, E. Tipping, J.F. Hackney and D. Beale, 1976).

Binding Sites↗
PubMed1976

The interactions of haem with ligandin and aminoazo-dye-binding protein A.

1. The interactions of ferriprotoporphyrin IX with ligandin and aminoazo-dye-binding protein A result in absorption spectra in the Soret region characteristic of the ligand in its monomeric state. 2. Both proteins are able to bind ferrous as well as ferric haem. 3. Ferriprotoporphyrin IX is bound at a single site on both proteins. At pH7.0, I 0.16M, difference-spectrophotometric measurements gave association constants of 10(7) and 4 X 10(6) LITRE/MOL FOR LIGANDIN AND PROTEin A respectively. Under the same conditions fluorescence-quenching experiments gave an association constant of 2 X 10(7) litre/mol for ligandin. 4. Bilirubin, bromosulphophthalein and oesterone sulphate each compete with haem for binding by the two proteins. 5. Ferriprotoporphyrin IX bound to both ligandin and protein A is able to form co-ordination complexes with CN-, but not, to any measurable extent, with either N3- or F-. From these results it is suggested that binding by the two proteins may not involve the haem iron atom. 6. Both haem-protein complexes give rise to measurable extrinsic Cotton effects in the Soret region. 7. The formation and properties of the ligandin- and protein A-haem complexes are compared with those of haem-albumin, haemoglobin, myoglobin and other haemoproteins.

Azo Compounds↗
PubMed1976

Spectroscopic studies of the binding of bilirubin by ligandin and aminoazo-dye-binding protein A.

Ligandin and aminoazo-dye-binding protein A both bind bilirubin at a single site. Quantitative studies of the interactions using difference spectrophotometry show that at pH 7.0, protein A binds the tetrapyrrole with an association constant (K) greater than or equal to 2 X 10(7) litre/mol, whereas binding by ligandin is slightly weaker (K = 7 X 10(6) litre/mol) at this pH. The protein-bilirubin complexes give rise to absorption and fluorescence spectra quite different from those of unbound bilirubin and also to large Cotton effects. It appears that on binding to both proteins, the ligand is forced into a rigid twisted configuration in a hydrophobic environment. Ligandin and protein A resemble serum albumin in their interactions with bilirubin.

Azo Compounds↗
PubMed1976

A low-molecular-weight protein from rat liver that resembles ligandin in its binding properties.

A protein of S20,W 1.6S and mol.wt. 14000, which binds covalently a metabolite of the aminoazodye carcinogen NN-dimethyl-4-amino-3'-methylazobenzene, was isolated from rat liver cytosol from both carcinogen-treated and normal rats. The protein binds non-covalently palmitoyl-CoA, fatty acids, bilirubin, sex steroids and their sulphates, bile acids and salts, bromosulphophthalein, diethylstilboestrol and 20-methylcholanthrene with a wide range of affinities. The protein is isolated as three components with isoelectric points of 5.0, 5.9 and 7.6 by a method involving isoelectric focusing. All three components have closely similar amino acid analyses, tryptic-peptide 'maps' and u.v. spectra. Each single component redistributes into all three on further electrophoresis. However, the three forms differ in their binding characteristics, the form of pI 7.6 having much the highest affinity for compounds bound non-covalently. The protein was identified immunologically in rat liver, small intestine, adipose tissue, skeletal muscle, myocardium and testis. The protein was compared with other hepatic binding-protein preparations of similar molecular weight.

Amino Acids↗
PubMed1975

The interaction between bovine serum albumin and surfactants.

1. Potassium n-decyl phosphate binds exothermically to bovine serum albumin at pH 7.0 to form a specific complex containing approx. 60 phosphate anions. 2. The formation of the complex is accompanied by changes in the u.v. difference spectrum of the protein. 3. At higher phosphate concentrations (above 0.4mM) surfactant molecules continue to be bound, and the protein undergoes a gross change in conformation. 4. n-Dodecyltri-methylammonium bromide binds endothermically to bovine serum albumin at pH7.0 but the extent of binding for a given free surfactant concentration is less than for the phosphate surfactant. 5. Binding is accompanied by a small change in the specific viscosity and by changes in the u.v. difference spectrum of the protein. 6. It is suggested that over the surfactant concentration ranges studied n-decyl phosphate ions first bind to the C-terminal part of the protein and then to the more compact N-terminal part whereas n-dodecyltrimethylammonium ions bind only to the C-terminal part of bovine serum albumin.

Dialysis↗
PubMed1975

Ligandin.

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Animals↗