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  • Portland Press Ltd.  (19)
  • Biology  (19)
  • 1
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    A novel aldehyde reductase with activity towards a metabolite of aflatoxin B1 is expressed in rat liver during carcinogenesis and following the administration of an anti-oxidant
    Portland Press Ltd. ; 1993
    In:  Biochemical Journal Vol. 292, No. 1 ( 1993-05-15), p. 13-18
    Details
    In: Biochemical Journal, Portland Press Ltd., Vol. 292, No. 1 ( 1993-05-15), p. 13-18
    Abstract: In contrast with fractions from control animals, an aldehyde reductase, which catalyses the reduction of aflatoxin B1-dihydrodiol, in the dialdehyde form at physiological pH values, to aflatoxin B1-dialcohol, is expressed in cytosolic fractions prepared from rat livers bearing pre-neoplastic lesions, or following treatment with the anti-oxidant ethoxyquin. This expression parallels the development of resistance to the toxin. Unlike the aflatoxin B1-dihydrodiol, the dialcohol does not undergo binding to protein. This enzyme activity could play a mechanistic role in hepatocarcinogenesis and chemoprotection in the rat. Correlated n.m.r. and m.s. spectra are provided in Supplementary Publication SUP 50171 (3 pages), which has been deposited at the British Library Document Supply Centre, Boston Spa, Wetherby, West Yorkshire LS23 7BQ, U.K., from whom copies can be obtained on the terms indicated in Biochem. J. (1993) 289, 9.
    Type of Medium: Online Resource
    ISSN: 0264-6021 , 1470-8728
    URL: Article
    DOI: 10.1042/bj2920013
    RVK:
    WA 15000
    Language: English
    Publisher: Portland Press Ltd.
    Publication Date: 1993
    detail.hit.zdb_id: 1473095-9
    SSG: 12
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  • 2
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    Absence of two membrane proteins containing extracellular thiol groups in Rhnull human erythrocytes
    Portland Press Ltd. ; 1983
    In:  Biochemical Journal Vol. 213, No. 1 ( 1983-07-01), p. 267-269
    Details
    In: Biochemical Journal, Portland Press Ltd., Vol. 213, No. 1 ( 1983-07-01), p. 267-269
    Abstract: Rhnull human erythrocytes lack all the antigens of the Rhesus blood-group system and are associated with mild chronic haemolytic anaemia. These erythrocytes have an abnormal shape and increased osmotic fragility. Labelling studies with the impermeant maleimide N-maleoylmethionine [35S]sulphone show that Rhnull erythrocytes lack two extracellular thiol-group-containing membrane components of apparent mol.wts. 32 000 and 34 000. Immunoprecipitation with mouse monoclonal antibody R6A (which reacts with all normal erythrocytes, but fails to react with Rhnull erythrocytes) specifically precipitates the 34 000-mol.wt. component from normal erythrocytes. Similar studies with human anti-Rh(D) serum shows that this antibody reacts with the 32 000-mol.wt. component. The results suggest that the R6A-binding polypeptide and the Rh(D) polypeptide may be involved in the maintenance of the shape and viability of the human erythrocyte.
    Type of Medium: Online Resource
    ISSN: 0264-6021
    URL: Article
    DOI: 10.1042/bj2130267
    RVK:
    WA 15000
    Language: English
    Publisher: Portland Press Ltd.
    Publication Date: 1983
    detail.hit.zdb_id: 1473095-9
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  • 3
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    The binding of amide substrate analogues to phospholipase A2. Studies by 13C-nuclear-magnetic-resonance and infrared spectroscopy
    Portland Press Ltd. ; 1992
    In:  Biochemical Journal Vol. 288, No. 1 ( 1992-11-15), p. 167-173
    Details
    In: Biochemical Journal, Portland Press Ltd., Vol. 288, No. 1 ( 1992-11-15), p. 167-173
    Abstract: (R)-(2-dodecanamidoisohexyl)phosphocholine (DAHPC), labelled with 13C at the amide carbonyl group, has been synthesized and its binding to bovine pancreatic phospholipase A2 (PLA2) studied by n.m.r. and i.r. spectroscopy. Two-dimensional 1H-n.m.r. spectra show that, in the presence of Ca2+, DAHPC binds to the active site of the enzyme in a similar manner to other phospholipid amide substrate analogues. The environment of the labelled carbonyl group has been investigated by a combination of 13C n.m.r. and difference-Fourier-transform i.r. spectroscopy. The carbonyl resonance shifts 3 p.p.m. downfield on the binding of DAHPC to PLA2. The carbonyl absorption frequency decreases by 14-18 cm-1, accompanied by a marked sharpening of the absorption band. These results indicate that the carbonyl bond undergoes significant polarization in the enzyme-ligand complex, facilitated by the enzyme-bound Ca2+ ion. This suggests that ground-state strain is likely to promote catalysis in the case of substrate binding. Simple calculations, based on the i.r. data, indicate that the carbonyl bond is weakened by 5-9 kJ.mol-1. This is the first report of observation of the amide vibration of a bound ligand against the strong background of protein amide vibrations.
    Type of Medium: Online Resource
    ISSN: 0264-6021 , 1470-8728
    URL: Article
    DOI: 10.1042/bj2880167
    RVK:
    WA 15000
    Language: English
    Publisher: Portland Press Ltd.
    Publication Date: 1992
    detail.hit.zdb_id: 1473095-9
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  • 4
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    Interactions between inhibitors of dihydrofolate reductase
    Portland Press Ltd. ; 1989
    In:  Biochemical Journal Vol. 258, No. 2 ( 1989-03-01), p. 335-342
    Details
    In: Biochemical Journal, Portland Press Ltd., Vol. 258, No. 2 ( 1989-03-01), p. 335-342
    Abstract: The binding of substrates and inhibitors to dihydrofolate reductase was studied by steady-state kinetics and high-field 1H-n.m.r. spectroscopy. A series of 5-substituted 2,4-diaminopyrimidines were examined and were found to be ‘tightly binding’ inhibitors of the enzyme (Ki less than 10(-9) M). Studies on the binding of 4-substituted benzenesulphonamides and benzenesulphonic acids also established the existence of a ‘sulphonamide-binding site’ on the enzyme. Subsequent n.m.r. experiments showed that there are two binding sites for the sulphonamides on the enzyme, one of which overlaps the coenzyme (NADPH) adenine-ring-binding site. An examination of the pH-dependence of the binding of sulphonamides to the enzyme indicated the influence of an ionizable group on the enzyme that was not directly involved in the sulphonamide binding. The change in pKa value from 6.7 to 7.2 observed on sulphonamide binding suggests the involvement of a histidine residue, which could be histidine-28.
    Type of Medium: Online Resource
    ISSN: 0264-6021 , 1470-8728
    URL: Article
    DOI: 10.1042/bj2580335
    RVK:
    WA 15000
    Language: English
    Publisher: Portland Press Ltd.
    Publication Date: 1989
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  • 5
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    The specific substance from Pneumococcus type 34 (41). The phosphodiester linkages
    Portland Press Ltd. ; 1968
    In:  Biochemical Journal Vol. 109, No. 4 ( 1968-10-01), p. 597-602
    Details
    In: Biochemical Journal, Portland Press Ltd., Vol. 109, No. 4 ( 1968-10-01), p. 597-602
    Abstract: 1. The phosphate groups in the type-specific substance S.34 from Pneumococcus type 34 (U.S. type 41) were shown to join the hydroxyl group at position 1 or 5 of ribitol and the hydroxyl group at position 3 of a d-galactofuranosyl residue in the next repeating unit. 2. A partial structure of the type-specific substance was derived. 3. New syntheses of d-galactose 2-phosphate and d-galactose 3-phosphate are described.
    Type of Medium: Online Resource
    ISSN: 0306-3283
    URL: Article
    DOI: 10.1042/bj1090597
    RVK:
    WA 15000
    Language: English
    Publisher: Portland Press Ltd.
    Publication Date: 1968
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  • 6
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    The pattern of plant annexin gene expression
    Portland Press Ltd. ; 1992
    In:  Biochemical Journal Vol. 281, No. 2 ( 1992-01-15), p. 501-505
    Details
    In: Biochemical Journal, Portland Press Ltd., Vol. 281, No. 2 ( 1992-01-15), p. 501-505
    Abstract: Peptide sequence data derived from a plant annexin, P34 [Smallwood, Keen & Bowles (1990) Biochem. J. 270, 157-161] was used to design amplimers for PCR. A unique fragment of 95 bp, amplified from tomato (Lycopersicon esculertum) genomic DNA, was used in Northern analyses and demonstrated a differential pattern of expression in vegetative tissues of tomato, potato (Solanum tuberosum) and barley (Hordeum vulgare). The tissue-specific abundance of the annexin transcript was found to correlate closely with abundance of annexin protein as revealed by their partial purification and analysis with antisera specific for annexins isolated from tomato suspension-culture cells.
    Type of Medium: Online Resource
    ISSN: 0264-6021 , 1470-8728
    URL: Article
    DOI: 10.1042/bj2810501
    RVK:
    WA 15000
    Language: English
    Publisher: Portland Press Ltd.
    Publication Date: 1992
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  • 7
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    Phe120 contributes to the regiospecificity of cytochrome P450 2D6: mutation leads to the formation of a novel dextromethorphan metabolite
    Portland Press Ltd. ; 2004
    In:  Biochemical Journal Vol. 380, No. 2 ( 2004-06-01), p. 353-360
    Details
    In: Biochemical Journal, Portland Press Ltd., Vol. 380, No. 2 ( 2004-06-01), p. 353-360
    Abstract: Although the residues that determine the preference of CYP2D6 (cytochrome P450 2D6) for compounds containing a basic nitrogen are well characterized, the contribution of other active site residues to substrate binding and orientation is less well understood. Our structural model of CYP2D6 identifies the aromatic residue Phe120 as a likely major feature of the active site. To examine the role of Phe120, mutants of CYP2D6 in which this residue has been substituted by alanine, leucine, tyrosine, serine, histidine, tryptophan or methionine residues have been prepared in bacterial membranes co-expressing human cytochrome NADPH cytochrome P450 oxidoreductase. The mutants have been characterized using the prototypical bufuralol 1´ hydroxylase and dextromethorphan O- and N-demethylase activities of CYP2D6. Larger effects on Km values are observed for dextromethorphan O-demethylation than for bufuralol 1´ hydroxylation, indicating that the Phe120 side chain is more important in dextromethorphan than in bufuralol binding. A role for this side chain in determining the regiospecificity of substrate oxidation was indicated by changes in the relative rates of O- and N-demethylation of dextromethorphan and, notably, by the formation of 7-hydroxy dextromethrophan, a novel dextromethorphan metabolite, in mutants in which it had been substituted. Computational studies of dextromethorphan binding to the active site of the Phe120→Ala mutant were carried out to throw light on the way in which the removal of this side chain leads to different modes of ligand binding.
    Type of Medium: Online Resource
    ISSN: 0264-6021 , 1470-8728
    URL: Article
    DOI: 10.1042/bj20040062
    RVK:
    WA 15000
    Language: English
    Publisher: Portland Press Ltd.
    Publication Date: 2004
    detail.hit.zdb_id: 1473095-9
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  • 8
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    Differential flux through the quinate and shikimate pathways. Implications for the channelling hypothesis
    Portland Press Ltd. ; 1992
    In:  Biochemical Journal Vol. 284, No. 1 ( 1992-05-15), p. 181-187
    Details
    In: Biochemical Journal, Portland Press Ltd., Vol. 284, No. 1 ( 1992-05-15), p. 181-187
    Abstract: The qutC gene encoding dehydroshikimate dehydratase has been constitutively overexpressed in Aspergillus nidulans from a range of 1-30-fold over the normal wild-type level. This overexpression leads to impaired growth in minimal medium which can be alleviated by the addition of aromatic amino acids to the medium. Overexpression of the qutC gene in mutant strains lacking protocatechuic acid (PCA) oxygenase leads to the build up of PCA in the medium, which can be measured by a simple assay. Measuring the rate of production of PCA in strains overproducing dehydroshikimate dehydratase and correlating this with the level of overproduction and impaired ability to grow in minimal medium lacking aromatic amino acids leads to the conclusion that (a) the metabolites 3-dehydroquinate and dehydroshikimate leak from the AROM protein at a rate comparable with the extent of flux catalysed by the AROM protein, (b) the AROM protein has a low-level channelling function probably as a result of the close juxtaposition of five active sites and (c) this channelling function is only physiologically significant under non-optimal conditions of nutrient supply and oxygenation, when the organism is in situ in its natural environment.
    Type of Medium: Online Resource
    ISSN: 0264-6021 , 1470-8728
    URL: Article
    DOI: 10.1042/bj2840181
    RVK:
    WA 15000
    Language: English
    Publisher: Portland Press Ltd.
    Publication Date: 1992
    detail.hit.zdb_id: 1473095-9
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  • 9
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    Loss of epidermal growth factor receptors and release of transforming growth factors do not correlate with sarcoma virus-transformation in clonally-related NIH/3T3-derived cell lines
    Portland Press Ltd. ; 1985
    In:  Biochemical Journal Vol. 229, No. 1 ( 1985-07-01), p. 119-125
    Details
    In: Biochemical Journal, Portland Press Ltd., Vol. 229, No. 1 ( 1985-07-01), p. 119-125
    Abstract: Transformation of NIH/3T3 cells by Kirsten murine sarcoma virus (MSV) caused a dramatic reduction in the number of cell-surface receptors for epidermal growth factor (EGF). However, the number of EGF receptors remained at a very low level in a non-tumourigenic revertant cell line isolated from the virus-transformed cells, indicating that an increase in EGF receptors is not a requirement for the phenotypic reversion of Kirsten MSV-transformed 3T3 cells. Serum-free conditioned medium from normal and virus-transformed cell lines contained similar amounts of cell growth-promoting activity as assayed by the ability to stimulate DNA synthesis in quiescent Swiss 3T3 cell cultures. However, the concentrated conditioned medium from these cell lines showed no evidence of beta-transforming growth factor (TGF) activity as assayed by promotion of anchorage-independent growth of untransformed normal rat kidney (NRK) fibroblasts in agarose. The cellular release of alpha-TGF activity was assayed by measuring the ability of concentrated conditioned medium to inhibit the binding of 125I-EGF to Swiss 3T3 cells. Conditioned medium protein from the virus-transformed cell line inhibited 125I-EGF binding but only to the same extent as conditioned medium protein prepared from the untransformed cell line. The alpha-TGF secretion by these cell lines was estimated to be 30-45-fold lower than the level of alpha-TGF released by a well-characterized alpha-TGF-producing cell line (3B11). These results suggest that the induction of TGF release is not a necessary event in the transformation of NIH/3T3 cells by Kirsten MSV.
    Type of Medium: Online Resource
    ISSN: 0264-6021 , 1470-8728
    URL: Article
    DOI: 10.1042/bj2290119
    RVK:
    WA 15000
    Language: English
    Publisher: Portland Press Ltd.
    Publication Date: 1985
    detail.hit.zdb_id: 1473095-9
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  • 10
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    19F-n.m.r. studies of 3′,5′-difluoromethotrexate binding to Lactobacillus casei dihydrofolate reductase. Molecular motion and coenzyme-induced conformational changes
    Portland Press Ltd. ; 1984
    In:  Biochemical Journal Vol. 217, No. 3 ( 1984-02-01), p. 659-666
    Details
    In: Biochemical Journal, Portland Press Ltd., Vol. 217, No. 3 ( 1984-02-01), p. 659-666
    Abstract: 19F-n.m.r. spectroscopy was used to study the binding of 3′,5′-difluoromethotrexate to dihydrofolate reductase (tetrahydrofolate dehydrogenase) from Lactobacillus casei. The benzoyl ring of the bound difluoromethotrexate was found to ‘flip’ about its symmetry axis, and the rate (7.3 × 10(3) s-1 at 298 K) and activation parameters for this process were determined by lineshape analysis of the 19F-n.m.r. spectrum at a series of temperatures in the range 273-308 K. The contributions to the barrier for this process are discussed. Addition of NADP+ or NADPH to form the enzyme-difluoromethotrexate-coenzyme ternary complex led to an increase in the rate of benzoyl ring flipping by a factor of 2.6-2.8-fold, and to substantial changes in the 19F-n.m.r. chemical shifts. The possible nature of the coenzyme-induced conformational changes responsible for these effects is discussed.
    Type of Medium: Online Resource
    ISSN: 0264-6021 , 1470-8728
    URL: Article
    DOI: 10.1042/bj2170659
    RVK:
    WA 15000
    Language: English
    Publisher: Portland Press Ltd.
    Publication Date: 1984
    detail.hit.zdb_id: 1473095-9
    SSG: 12
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