Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
Filter
  • Portland Press Ltd.  (13)
  • 1
    Online Resource
    Online Resource
    Portland Press Ltd. ; 1995
    In:  Clinical Science Vol. 88, No. 1 ( 1995-01-01), p. 73-79
    In: Clinical Science, Portland Press Ltd., Vol. 88, No. 1 ( 1995-01-01), p. 73-79
    Abstract: 1. The ratio of the methyl donor, S-adenosylmethionine, to the co-product, S-adenosylhomocysteine (the methylation ratio) is known to control the activity of methyltransferases in tissues. Inactivation of the vitamin B12-dependent enzyme, methionine synthase, reduces the methylation ratio in rats and pigs in vivo. 2. We have determined the effect that such alterations have on neural protein ‘O’ and ‘N’ methyltransferases using an in vitro assay in rats, pigs and humans in the presence of the normal methylation ratio and the abnormal methylation ratios found experimentally in vivo in rats and pigs. 3. The methylation ratio found in the neural tissues of vitamin B12-inactivated pigs significantly inhibits the protein methyltransferases of pigs and humans. 4. By contrast, the altered methylation ratio found in vitamin B12-inactivated rats only marginally inhibits the equivalent rat methyltransferases. 5. This is consistent with the induction of a myelopathy by such treatment in pigs and humans, but not in the rat. 6. Dietary supplements of methionine given to vitamin B12-inactivated pigs have been shown to prevent the myelopathy in vivo by both elevating the neural S-adenosylmethionine level and resetting the methylation ratio. We find in our in vitro assay that these events reinstate the methyltransferase activity to near normal levels, thus explaining its protective effect in vivo.
    Type of Medium: Online Resource
    ISSN: 0143-5221 , 1470-8736
    Language: English
    Publisher: Portland Press Ltd.
    Publication Date: 1995
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 2
    In: Clinical Science, Portland Press Ltd., Vol. 82, No. 1 ( 1992-01-01), p. 93-97
    Abstract: 1. Pigs were maintained in air or in an atmosphere of nitrous oxide which dramatically changes the S-adenosyl-l-methionine to S-adenosyl-l-homocysteine ratio in neural tissues. Samples of cerebrospinal fluid, cortex, cerebellum and spinal cord were then extracted and analysed for S-adenosyl-l-methionine and S-adenosyl-l-homocysteine. Regression analyses were carried out on values obtained in cerebrospinal fluid and in neural tissues. 2. Highly significant correlations were obtained between levels of S-adenosyl-l-homocysteine (r2 = 0.42-0.69; P & lt; 0.001) and S-adenosyl-l-methionine/S-adenosyl-l-homocysteine ratios (r2 = 0.56-0.65; P & lt; 0.001) in cerebrospinal fluid and levels and ratios in cortex, cerebellum and spinal cord. The levels of S-adenosyl-l-methionine did not show a significant correlation. 3. We conclude that the ratio of these metabolites in the cerebrospinal fluid may reflect the ratio in the central nervous system and we suggest that this may also be true in human tissues. This finding will permit the determination of the probable methylation ratio in the central nervous system in human conditions, such as vitamin B12 deficiency and acquired immune deficiency syndrome, where a similar myelopathy occurs to that seen in the nitrous oxide-treated pig. All three myelopathies may arise from an inhibition of methyltransferases involved in the synthesis of myelin that would occur when the methylation ratio is reduced.
    Type of Medium: Online Resource
    ISSN: 0143-5221 , 1470-8736
    Language: English
    Publisher: Portland Press Ltd.
    Publication Date: 1992
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 3
    In: Clinical Science, Portland Press Ltd., Vol. 88, No. 4 ( 1995-04-01), p. 471-477
    Abstract: 1. Pigs treated with nitrous oxide for periods of 1, 2 and 4 months demonstrated markedly reduced levels of methionine synthase and concomitant reduction in the ratio of S-adenosylmethionine to S-adenosylhomocysteine, the methylation ratio, at all time intervals. 2. Both ‘O’ and ‘N’ methylations were significantly reduced in pigs after 4 months in nitrous oxide but not after shorter periods. 3. Hypomethylation correlated with the development of clinical ataxia, but was absent when the pigs were clinically normal. It also only occurred when the S-adenosylmethionine level fell. 4. Rats maintained in nitrous oxide for 4 months showed a marked reduction of methionine synthase but no reduction in the methylation ratio or in brain hypomethylation. None of the rats became clinically ataxic. 5. Using an exogenous protein as a methyl group acceptor, it was demonstrated in an in vitro assay that the methyltransferase enzymes responsible for brain ‘O’ and ‘N’ methylation were not affected per se by nitrous oxide treatment. 6. It is concluded that reduction of the methylation ratio in the brain of pigs as a consequence of methionine synthase inhibition leads to brain hypomethylation. This hypomethylation could affect critical components of nerve tissue, inducing the vacuolar myelopathic changes seen in the spinal cord of these animals, which mimic those of subacute combined degeneration in man.
    Type of Medium: Online Resource
    ISSN: 0143-5221 , 1470-8736
    Language: English
    Publisher: Portland Press Ltd.
    Publication Date: 1995
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 4
    Online Resource
    Online Resource
    Portland Press Ltd. ; 1993
    In:  Biochemical Journal Vol. 290, No. 3 ( 1993-03-15), p. 723-729
    In: Biochemical Journal, Portland Press Ltd., Vol. 290, No. 3 ( 1993-03-15), p. 723-729
    Abstract: The Fv fragment of the antibody B72.3 has been produced by expression in both a mammalian and microbial system, namely Chinese hamster ovary (CHO) cells and Escherichia coli. In both cases secretion of the Fv into the culture medium was achieved, with equivalent amounts of Vh and Vl produced. The yield of Fv from CHO cells was 4 mg/l in roller-bottle culture. E. coli proved to be a more productive system with yields of 40 mg/l in shake flasks rising to 450 mg/l in fermentations. B72.3 Fv from both sources was capable of binding to antigen with similar binding ability to the Fab' fragment. A detailed sedimentation analysis, both by velocity and equilibrium techniques, revealed that the two domains of Fv are associated at high concentrations at pH values close to neutral, but dissociate at concentrations lower than approx. 0.5 mg/ml. Individual Vh or Vl polypeptides are not able to bind to the antigen and thus these results suggest that the antigen promotes assembly of Fv at the low concentrations used in the antigen-binding assays. At a pH value of 1.9, Vh and Vl are completely dissociated even at very high concentrations and are apparently unfolded at low solute concentrations. Small-angle X-ray scattering was used to measure a radius of gyration of 1.75 +/- 0.2 nm (17.5 +/- 2 A) for Fv.
    Type of Medium: Online Resource
    ISSN: 0264-6021 , 1470-8728
    RVK:
    Language: English
    Publisher: Portland Press Ltd.
    Publication Date: 1993
    detail.hit.zdb_id: 1473095-9
    SSG: 12
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 5
    Online Resource
    Online Resource
    Portland Press Ltd. ; 1983
    In:  Clinical Science Vol. 65, No. 3 ( 1983-09-01), p. 303-305
    In: Clinical Science, Portland Press Ltd., Vol. 65, No. 3 ( 1983-09-01), p. 303-305
    Abstract: 1. Folate deficiency is reported in association with certain malignant tumours, and it has been suggested that this arises from increased folate turnover and catabolism in such circumstances. 2. Using an experimental animal model to determine the rate of catabolism of [3H]pteroylglutamate (folic acid) by the quantitative estimation of the two urinary catabolites p-[3H]aminobenzoylglutamate and [3H] acetamidobenzoylglutamate, we have measured the rate of folate catabolism in mice with ascitic tumours. 3. There was a significant increase in the rate of catabolism in the mice with tumours compared with controls over a 10 day period. This was associated with the accumulation of ascitic fluid and an increase in the number of tumour cells in the treated animals. 4. The increase in catabolism appeared to be due to increased cell turnover of the tumour rather than an increase in cell mass, as the increase in mass of the tumour was negligible.
    Type of Medium: Online Resource
    ISSN: 0143-5221 , 1470-8736
    Language: English
    Publisher: Portland Press Ltd.
    Publication Date: 1983
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 6
    Online Resource
    Online Resource
    Portland Press Ltd. ; 1973
    In:  Clinical Science Vol. 45, No. 5 ( 1973-11-01), p. 625-631
    In: Clinical Science, Portland Press Ltd., Vol. 45, No. 5 ( 1973-11-01), p. 625-631
    Abstract: 1. The two diastereoisomers of 5-methyltetrahydropteroylglutamate, the form of folate that predominates in food and bile, were prepared chemically. 2. Their intestinal absorption was compared by means of the urinary-excretion method of 3H-labelled compounds and it was found that the naturally occurring biologically active isomer was excreted to a greater extent. Studies of the clearance of the two forms after intravenous injection showed that this difference was due to preferential intestinal absorption of the naturally occurring isomer. 3. In four patients with coeliac disease, the absorption of the naturally occurring isomer was depressed to the same range as the inactive isomer. 4. Since the two diastereoisomers are chemically inseparable, these results indicate that a carrier-mediated process is involved in the human intestinal absorption of this form of reduced folate.
    Type of Medium: Online Resource
    ISSN: 0301-0538
    Language: English
    Publisher: Portland Press Ltd.
    Publication Date: 1973
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 7
    Online Resource
    Online Resource
    Portland Press Ltd. ; 2002
    In:  Biochemical Society Transactions Vol. 30, No. 4 ( 2002-08-01), p. 512-516
    In: Biochemical Society Transactions, Portland Press Ltd., Vol. 30, No. 4 ( 2002-08-01), p. 512-516
    Abstract: Monoclonal antibodies are increasingly being used as therapeutic agents in a wide range of indications, including oncology, inflammation and infectious disease. In most cases the basis of the therapeutic function is the high degree of specificity and affinity the antibody-based drug has for its target antigen. However, the mechanism of action (MOA), the way the drug takes advantage of this specificity to mediate a therapeutic effect, varies considerably from drug to drug. Three basic potential categories of MOAs exist: antagonists, agonists and specific delivery mechanisms to target an active function to a particular cell type. The latter functions include selective cell killing, based on Fc-mediated events, recruitment of effector cells, and drug or radioisotope delivery. The majority of these mechanisms are not necessarily optimally mediated by an IgG structure; clearly, in the case of antibody-dependent cellular cytotoxicity or complement-mediated lysis, Fc is required. However, Fab fragments (the fragment comprising one antigen-binding arm of the Y-shaped IgG molecule) can be formatted to mediate most mechanisms and have the advantage that valency and half-life can be controlled to simplify the drug and address only the mechanism required. Moreover, Fab fragments can be produced in microbial expression systems which address manufacturing issues such as scale of supply and cost of goods.
    Type of Medium: Online Resource
    ISSN: 0300-5127 , 1470-8752
    Language: English
    Publisher: Portland Press Ltd.
    Publication Date: 2002
    SSG: 12
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 8
    Online Resource
    Online Resource
    Portland Press Ltd. ; 1985
    In:  Clinical Science Vol. 69, No. 3 ( 1985-09-01), p. 287-292
    In: Clinical Science, Portland Press Ltd., Vol. 69, No. 3 ( 1985-09-01), p. 287-292
    Abstract: 1. Methionine synthetase was measured in the mucosal cells of the rat duodenum, jejunum and ileum by a previously employed method for mucosal cell isolation. No activity was found in these cells. 2. When a dual buffer system for the isolation of villous and crypt cell population was substituted, however, methionine synthetase was found to be active in the duodenum, jejunum and ileum, both in the villous and crypt cell populations. The activity was significantly higher in the crypt cells than in the villous cells throughout the intestine, and higher levels were found in the ileum than in the duodenum or jejunum. 3. As had been previously reported for the rat liver, nitrous oxide in vivo reduced the enzyme activity in both the villous and crypt cell populations, suggesting a role in vivo for the enzyme. We conclude that methionine synthetase is both present and active in the small intestinal mucosal cells of the rat.
    Type of Medium: Online Resource
    ISSN: 0143-5221 , 1470-8736
    Language: English
    Publisher: Portland Press Ltd.
    Publication Date: 1985
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 9
    Online Resource
    Online Resource
    Portland Press Ltd. ; 2002
    In:  Biochemical Society Transactions Vol. 30, No. 3 ( 2002-06-01), p. A68-A68
    In: Biochemical Society Transactions, Portland Press Ltd., Vol. 30, No. 3 ( 2002-06-01), p. A68-A68
    Type of Medium: Online Resource
    ISSN: 0300-5127 , 1470-8752
    Language: English
    Publisher: Portland Press Ltd.
    Publication Date: 2002
    SSG: 12
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 10
    Online Resource
    Online Resource
    Portland Press Ltd. ; 1977
    In:  Clinical Science Vol. 52, No. 1 ( 1977-01-01), p. 83-86
    In: Clinical Science, Portland Press Ltd., Vol. 52, No. 1 ( 1977-01-01), p. 83-86
    Abstract: 1. The recent suggestions that folate polyglutamate biosynthesis demonstrated in vivo with [3′5′9(n)-3H]folic acid is due to exchange and cannot be achieved with [2-14C] folic acid has been demonstrated to be untrue. 2. The compounds formed with both types of radioactive tracer have been shown to be folate polyglutamates from their elution position from precalibrated ion-exchange columns and their susceptibility to hydrolysis by a γ-carboxypeptidase (conjugase) from human sera. 3. By the use of the methods involving [2-14C]folic acid, reported by others to give only folate monoglutamates, we have been able to demonstrate clearly the presence of folate polyglutamates.
    Type of Medium: Online Resource
    ISSN: 0301-0538
    Language: English
    Publisher: Portland Press Ltd.
    Publication Date: 1977
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
Close ⊗
This website uses cookies and the analysis tool Matomo. Further information can be found on the KOBV privacy pages