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T J Mantle

Publications and source records attributed to T J Mantle.

At least 37 records · Page 2Linked to original sources
PubMed1993

Inactivation of mouse liver glutathione S-transferase YfYf (Pi class) by ethacrynic acid and 5,5'-dithiobis-(2-nitrobenzoic acid).

Mouse liver glutathione S-transferase YfYf (Pi class) reacts with [14C]ethacrynic acid to form a covalent adduct with a stoichiometry of 1 mol per mol of subunit. Proteolytic digestion of the enzyme-[14C]ethacrynic acid adduct with V8 protease produced an 11 kDa fragment containing radioactivity. Sequencing revealed this to be an N-terminal peptide (minus the first 15 residues, terminating at Glu-112) which contains only one cysteine residue (Cys-47). This is tentatively identified as the site of ethacrynic attachment. Kinetic studies reveal that glutathione S-conjugates protect against inactivation by ethacrynic acid, but the level of protection is not consistent with their potency as product inhibitors. A model is proposed in which glutathione S-conjugates and ethacrynic acid compete for the free enzyme, and a second molecule of ethacrynic acid reacts covalently with the enzyme-ethacrynic acid complex. The native protein contains one thiol reactive with 5,5'-dithiobis-(2-nitrobenzoic acid) at neutral pH. The resultant mixed disulphide, like the ethacrynic acid adduct, is inactive, but treatment with cyanide (which incorporates on a mol for mol basis) restores activity to 35% of that of the native enzyme.

Amino Acid Sequence↗
PubMed1993

Effect of lead acetate and carbon particles on the expression of glutathione S-transferase YfYf in rat liver.

Administration of intracardiac lead acetate produces a complex response in glutathione S-transferase (GST) YfYf expression in rat liver. The earliest response, an elevation of GST expression in Kupffer cells, can be mimicked by administering a suspension of carbon particles. The second effect of lead acetate administration is a marked elevation of GST YfYf in some but not all hepatocytes (the 'patchy' response). This effect is most marked 48-76 h after administration of a single dose of lead acetate and is easily detected by immunoblotting. Dexamethasone down-regulates the lead response in hepatocytes.

Animals↗
PubMed1991

The initial-rate kinetics of mouse glutathione S-transferase YfYf. Evidence for an allosteric site for ethacrynic acid.

Mouse glutathione S-transferase GST YfYf (an orthologue of GST P or 7-7 in the rat and of GST pi in the human) was found to have a subunit Mr of 24,500 and cross-reacted with anti-(rat GST YfYf). N-Terminal analysis showed a close similarity to the rat, human and bovine orthologues. On isoelectric focusing the native enzyme had a pI of 8.3 and a pI of 7.3 in the presence of urea. Initial-rate studies with 1-chloro-2,4-dinitrobenzene (CDNB) and GSH as substrates and inhibition studies with the product of the enzyme-catalysed conjugation of CDNB and GSH, S-(2,4-dinitrophenyl)glutathione, indicated a rapid-equilibrium random mechanism for the enzyme. The diuretic drug ethacrynic acid was found to be simultaneously a competitive inhibitor and an uncompetitive activator of the enzyme (with CDNB as the substrate whose concentration was varied). By using a computer simulation program (EKPLOT) a model was developed that would explain the experimental data. It is proposed that ethacrynic acid can compete with CDNB at the active site but simultaneously bind to an allosteric site on the enzyme, causing an elevation in the Vmax. for the conjugation of CDNB and GSH. The implications of such an activation mechanism for an enzyme potentially conjugating a range of xenobiotic compounds are discussed.

Allosteric Site↗
PubMed1989

The development of glutathione S-transferase subunits in rat liver. Sensitive detection of the major subunit forms of rat glutathione S-transferase by using an e.l.i.s.a. method.

The development of the subunits of glutathione S-transferase in rat liver shows that there is a co-ordinated development of the Ya, Yb1, Yb2 and Yc subunits but that the Yf and Yk subunits show unique patterns of development. The Yk subunit is the only form that is expressed at relatively high levels during the foetal period as well as during the adult period. In contrast with all other forms, the Yf subunit in the rat declines rapidly during the last few days before parturition and is virtually undetectable in hepatocytes of adult animals. The expression of the Yf subunit in foetal liver presents a 'patchy' appearance that is similar to that induced by the administration of lead acetate and may reflect cell-cycle-associated regulation of expression.

Aging↗
PubMed1989

Purification of a class C A-type beta-lactamase from a derepressed strain of Enterobacter cloacae. Comparison of the wild-type and mutant enzyme with those from strains P99, 208 and GN7471.

Enterobacter cloacae strain 5822 expresses low levels of a class C beta-lactamase which can be induced 100-fold by imipenem. Mutants that constitutively express high levels of beta-lactamase can be selected on aztreonam or cefotaxime. The beta-lactamase from one such mutant (5822M2) has been purified to homogeneity and compared on the basis of subunit Mr, pI, substrate specificity, inhibitor sensitivity and immunological cross-reactivity with the enzyme from strains P99, GN7471 and 208, which have been studied previously. The enzyme from strain 5822M2 is clearly related to these other forms and is of the A-type according to the criteria of Seeberg, Tolxdorff-Neutzling & Wiedemann [Antimicrob. Agents Chemother. (1983) 23, 918-925]. The enzyme from the wild-type strain (5822) is shown to be identical to that found in the depressed strain (5822M2), indicating that the mutation is in a regulatory gene. A detailed analysis of the kinetics of the enzyme from strain 5822M2 shows that all of the beta-lactams studied are substrates and that a mechanism involving the formation of an acyl-enzyme is probably applicable in every case. The substrates however can clearly be grouped into two classes, i.e. 'good' substrates with kcat. values of 80-1200 s-1 and 'poor' substrates/good inhibitors with kcat. values of 0.009-0.00007 s-1. The permeability barrier to aztreonam is 4-fold less in the derepressed strain when compared with the wild-type strain. This is associated with significant changes in the expression of outer membrane porins. The observed resistance in the derepressed mutant appears to be linked to the elevated levels of beta-lactamase (3000-fold) rather than to the modest changes in the permeability barrier.

Bacterial Outer Membrane Proteins↗
PubMed1989

The kinetics of ox kidney biliverdin reductase in the pre-steady state. Evidence that the dissociation of bilirubin is the rate-determining step.

When the production of bilirubin by biliverdin reductase was monitored at 460 nm by stopped-flow spectrophotometry a 'burst' was observed with a first-order rate constant at pH 8 of 20 s-1. The steady-state rate was established on completion of the 'burst'. When the reaction was monitored at 401 nm there was no observed steady-state rate, but a diminished pre-steady-state 'burst' reaction was still seen with a rate constant of 22 s-1. We argue that the rate-limiting reaction is the dissociation of bilirubin from an enzyme.NADP+.bilirubin complex. With NADPH as the cofactor the hydride-transfer step was shown to exhibit pH-dependence associated with an ionizing group with a pK of 7.2. The kinetics of NADPH binding to the enzyme at pH 7.0 were measured by monitoring the quenching of protein fluorescence on binding the coenzyme.

Animals↗
PubMed1988

The reaction mechanism of bovine kidney biliverdin reductase.

The steady-state kinetics of biliverdin reductase can be studied in detail at pH 9 as under these conditions the Km for biliverdin is high enough to obtain reliable measurements of the initial rate in the absence of any biliverdin binding proteins. The initial rate kinetics and the product-inhibition studies are consistent with an ordered sequential mechanism provided the biliverdin concentration was below 20 microM. Above this concentration significant flux occurs through a substrate inhibition pathway involving an enzyme-NAD(P)-biliverdin complex. Chloride is shown to cause a significant activation of the enzyme under certain conditions and this is shown to result from an inability of biliverdin to bind to an enzyme-NAD-chloride complex.

Animals↗
PubMed1988

Some physical and immunological properties of ox kidney biliverdin reductase.

The liver, kidney and spleen of the mouse and rat and the kidney and spleen of the ox express a monomeric form of biliverdin reductase (Mr 34,000), which in the case of the ox kidney enzyme exists in two forms (pI 5.4 and 5.2) that are probably charge isomers. The livers of the mouse and rats express, in addition, a protein (Mr 46,000) that cross-reacts with antibodies raised against the ox kidney enzyme and may be related to form 2 described by Frydman, Tomaro, Awruch & Frydman [(1983) Biochim. Biophys. Acta 759, 257-263]. Higher-Mr forms appear to exist in the guinea pig and hamster. The ox kidney enzyme has three thiol groups, of which two are accessible to 5,5'-dithiobis-(2-nitrobenzoate) in the native enzyme. Immunocytochemical analysis reveals that biliverdin reductase is localized in proximal tubules of the inner cortex of the rat kidney. Biliverdin reductase antiserum also stains proximal tubules in human and ox kidney. The staining of podocytes in glomeruli of ox kidney with antiserum to aldose reductase is particularly prominent. The localization of biliverdin reductase in the inner cortical zone of rat kidney is similar to that described for glutathione S-transferase YfYf, and it is suggested that one function of this 'intracellular binding protein' may be to maintain a low free concentration of biliverdin to allow biliverdin reductase to operate efficiently.

Animals↗
PubMed1987

Glutathione S-transferase subunits in the mouse and their catalytic activities towards reactive electrophiles.

The glutathione S-transferases (GST) are a major, multi-gene, group of detoxication proteins. A rapid, two-step purification, that employs S-hexylglutathione affinity chromatography and hydroxyapatite HPLC, is described for the GST isoenzymes in mouse liver. The major hepatic forms comprise Yf(Mr 24,500)-, Ya(Mr 26,000)- and Yb(Mr 27,000)-type subunits. The isoelectric points of the Yf, Ya and Yb dimers are 8.6, 9.2 and 7.8-8.2 respectively. Immunochemical experiments showed the purified mouse subunits cross-reacted with antisera raised against rat GST subunits that possessed equivalent molecular masses; the subunit sizes of the distinct subunit types are conserved between these two species. The catalytic activities of the purified mouse GST subunits are described. In common with other species the mouse GST are subject to tissue-specific expression. However, only mouse liver and not rat, guinea pig, hamster or human livers express the Yf polypeptide. The significance of this difference is unclear but, in the rat, the Yf subunit can serve as a marker for pre-neoplastic hepatocellular carcinogenesis.

Animals↗
PubMed1986

Anomalous electrophoretic behaviour of the glutathione S-transferase Ya and Yk subunits isolated from man and rodents. A potential pitfall for nomenclature.

GSH S-transferases are dimeric enzymes. The subunits in the rat are resolved into six types, designated Yf, Yk, Ya, Yn, Yb and Yc, by discontinuous SDS/polyacrylamide-gel electrophoresis [Hayes (1986) Biochem. J. 233, 789-798]. The relative electrophoretic mobility of the Ya and Yk subunits is dependent on the amount of cross-linker (NN'-methylenebisacrylamide) in the resolving gel. At low degrees of cross-linking, CBis 0.6% (w/w), the Yk and Ya subunits possess a faster anodal mobility than do the Yf, Yn, Yb and Yc subunits (i.e. order of mobility Yk greater than Ya greater than Yf greater than Yn greater than Yb greater than Yc), whereas at higher degrees of cross-linking, CBis 5.0% (w/w), Yf subunits possess the fastest mobility (i.e. order of mobility Yf greater than Yk greater than or equal to Yn greater than Yb greater than or equal to Ya greater than Yc). Resolving gels that contain low concentrations of cross-linker [CBis 0.6% (w/w)] allow the resolution of a hitherto unrecognized polypeptide that is isolated by S-hexyl-GSH-Sepharose affinity chromatography. This new polypeptide, which we have designated Yb, is normally obscured by the main Yb band in resolving gels that comprise concentrations of cross-linker of at least CBis 1.6% (w/w). The Ya- and Yb-type subunits in guinea pig, mouse, hamster and man were identified by immuno-blotting and their apparent Mr values in different electrophoresis systems were determined. The Ya subunits in all species studied possess a variable cross-linker-dependent mobility during electrophoresis. Since the transferase subunits are currently classified according to their mobilities during SDS/polyacrylamide-gel electrophoresis, it is apparent that the variable electrophoretic behaviour of the Ya and Yk subunits may lead to the mis-identification of enzymes.

Acrylamides↗
PubMed1986

Use of immuno-blot techniques to discriminate between the glutathione S-transferase Yf, Yk, Ya, Yn/Yb and Yc subunits and to study their distribution in extrahepatic tissues. Evidence for three immunochemically distinct groups of transferase in the rat.

The glutathione S-transferases are dimeric enzymes whose subunits can be defined by their mobility during sodium dodecyl sulphate/polyacrylamide-gel electrophoresis as Yf (Mr 24,500), Yk (Mr 25,000), Ya (Mr 25,500), Yn (Mr 26,500), Yb1 (Mr 27,000), Yb2 (Mr 27,000) and Yc (Mr 28,500) [Hayes (1986) Biochem. J. 233, 789-798]. Antisera were raised against each of these subunits and their specificities assessed by immuno-blotting. The transferases in extrahepatic tissues were purified by using, sequentially, S-hexylglutathione and glutathione affinity chromatography. Immune-blotting was employed to identify individual transferase polypeptides in the enzyme pools from various organs. The immuno-blots showed marked tissue-specific expression of transferase subunits. In contrast with other subunits, the Yk subunit showed poor affinity for S-hexylglutathione-Sepharose 6B in all tissues examined, and subsequent use of glutathione and glutathione affinity chromatography. Immuno-blotting was employed to identify a new cytosolic polypeptide, or polypeptides, immunochemically related to the Yk subunit but with an electrophoretic mobility similar to that of the Yc subunit; high concentrations of the new polypeptide(s) are present in colon, an organ that lacks Yc.

Animals↗
PubMed1986

Inhibition of hepatic and extrahepatic glutathione S-transferases by primary and secondary bile acids.

Glutathione S-transferases are a complex family of dimeric proteins that play a dual role in cellular detoxification; they catalyse the first step in the synthesis of mercapturic acids, and they bind potentially harmful non-substrate ligands. Bile acids are quantitatively the major group of ligands encountered by the glutathione S-transferases. The enzymes from rat liver comprise Yk (Mr 25 000), Ya (Mr 25 500), Yn (Mr 26 500), Yb1, Yb2 (both Mr 27 000) and Yc (Mr 28 500) monomers. Although bile acids inhibited the catalytic activity of all transferases studied, the concentration of a particular bile acid required to produce 50% inhibition (I50) varies considerably. A comparison of the I50 values obtained with lithocholate (monohydroxylated), chenodeoxycholate (dihydroxylated) and cholate (trihydroxylated) showed that, in contrast with all other transferase monomers, the Ya subunit possesses a relatively hydrophobic bile-acid-binding site. The I50 values obtained with lithocholate and lithocholate 3-sulphate showed that only the Ya subunit is inhibited more effectively by lithocholate than by its sulphate ester. Other subunits (Yk, Yn, Yb1 and Yb2) were inhibited more by lithocholate 3-sulphate than by lithocholate, indicating the existence of a significant ionic interaction, in the bile-acid-binding domain, between (an) amino acid residue(s) and the steroid ring A. By contrast, increasing the assay pH from 6.0 to 7.5 decreased the inhibitory effect of all bile acids studied, suggesting that there is little significant ionic interaction between transferase subunits and the carboxy group of bile acids. Under alkaline conditions, low concentrations (sub-micellar) of nonsulphated bile acids activated Yb1, Yb2 and Yc subunits but not Yk, Ya and Yn subunits. The diverse effects of the various bile acids studied on transferase activity enables these ligands to be used to help establish the quaternary structure of individual enzymes. Since these inhibitors can discriminate between transferases that appear to be immunochemically identical (e.g. transferases F and L), bile acids can provide information about the subunit composition of forms that cannot otherwise be distinguished.

Animals↗
PubMed1986

Kinetic studies on the major form of aldehyde reductase in ox kidney: a general kinetic mechanism to explain substrate-dependent mechanisms and the inhibition by anticonvulsants.

The inhibition of the major form of ox kidney aldehyde reductase (AR 1) by sodium barbitone revealed linear mixed kinetics. This behaviour is distinct from the non-linear intercept effect we reported for valproate [Daly and Mantle (1982) Biochem. J. 205, 381]. 4-Carboxybenzaldehyde exhibits partial uncompetitive substrate inhibition. These results are discussed in terms of a model that involves nucleotide-induced isomerization and an additional flux (with some substrates and inhibitors) through an enzyme.nucleotide.substrate/inhibitor ternary complex.

Aldehyde Dehydrogenase↗
PubMed1984

Studies on the glutathione S-transferase activity associated with rat liver mitochondria.

The major proportion of rat liver glutathione S-transferase is cytosolic. Carefully washed mitochondria contain 0.25-0.47% of the cytosolic activity. Subfractionation of washed mitochondria using digitonin treatment revealed that glutathione S-transferase release did not parallel that of any of the mitochondrial marker enzymes. Glutathione S-transferase release paralleled that of lactate dehydrogenase, suggesting that these 'mitochondrial' activities are due to loosely bound cytoplasmic forms.

Animals↗
PubMed1984

On the possible role of biliverdin stimulation of cyclic AMP levels as a trigger for liver regeneration in the rat.

Contrary to a recent report by Okazaki et al. (Biochem. biophys. Res. Commun., 1978, 81, 512-520) we show that high concentrations of biliverdin (100 mg/kg, i.p.) slightly reduce the mitotic rate in rat liver. Adenylate cyclase and both the "high Km" and "low Km" phosphodiesterase of rat liver plasma membranes are inhibited by high concentrations of biliverdin. Biliverdin has no effect on cyclic AMP production in isolated hepatocytes. An intracellular binding protein (glutathione-S-transferase B) is shown to bind biliverdin providing a mechanism for maintaining a low free intracellular concentration of the tetrapyrrole analogous to that of albumin in plasma. In conclusion, these results are not consistent with a role for biliverdin in stimulating liver regeneration in the rat via a mechanism involving elevated cyclic AMP levels.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1984

Selective induction of glutathione S-transferase D in rat testis by phenobarbital.

Testis cytosol is shown to contain the Yb2Yb2 -homodimer glutathione S-transferase D in addition to the previously described glutathione S-transferases A ( Yb1Yb1 ) and C ( Yb1Yb2 ). Treatment of rats with phenobarbital induces the level of glutathione S-transferase D in testis with no increase in the activities of glutathione S-transferases A and C. This result indicates a specific induction of the Yb2 subunit in testis, in contrast with the situation in rat liver, where phenobarbital specifically induces the Yb1 subunit.

Animals↗