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  • 1
    ISSN: 1432-072X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Description / Table of Contents: Zusammenfassung Aus einem Rohextrakt von Hydrogenomonas eutropha Stamm H16-Fructosezellen wurden eine NADP- und eine NAD-spezifische Isocitrat-Dehydrogenase teilweise gereinigt und getrennt. Beide Enzyme sind in ihrer Affinität zum Isocitrat und zu NADP bzw. NAD sehr ähnlich. Beide Enzyme werden durch ATP gehemmt, das NADP-abhängige Enzym wird außerdem durch AMP und ADP aktiviert. Das NAD-abhängige Enzym wird durch NADH2 gehemmt. Beide Enzyme werden stark gehemmt, wenn Glyoxylat und Oxalacetat gemeinsam dem Reaktionsgemisch zugesetzt werden.
    Notes: Summary From crude extracts of fructose-grown cells of Hydrogenomonas eutropha strain H 16 both a NADP- and a NAD-specific isocitrate dehydrogenase have been separated and partially purified. With respect to their affinity for isocitrate and NADP or NAD, respectively, both enzymes are very similar. Both enzymes are inhibited by ATP, the NADP-dependent enzyme is activated by AMP and ADP in addition. The NAD-specific enzyme is inhibited by NADH2. Both enzymes are highly inhibited if glyoxylate and oxalacetate are concomitantly added to the enzyme reaction mixture.
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  • 2
    ISSN: 1432-072X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Description / Table of Contents: Zusammenfassung 1. Die Aktivitäten der Enzyme des Tricarbonsäure-Cyclus wurden in Rohextrakten aus Zellen von Hydrogenomonas eutropha H 16 nach Wachstum auf Fructose, Malat, Succinat, Glutamat, Acetat, Nährbouillon, Allantoin und nach autotrophem Wachstum bestimmt. Die Aktivität der meisten Enzyme ist nach Wachstum auf Acetat, Succinat oder Malat höher als in Fructose- oder autotroph gewachsenen Zellen. Weder in Nährbouillon noch in einem Fructose-Glutamat-Medium wurde eine Repression der Enzymsynthese beobachtet. 2. Die spezifischen Aktivitäten der Isocitrat-Dehydrogenasen mit NADP und NAD als Cofaktoren und der α-Ketoglutarat-Dehydrogenase wurden auch in Über-gangsexperimenten auf folgenden Substratpaaren ermittelt: autotroph zu Malat, Fructose zu Malat und umgekehrt; autotroph zu autotroph-Malat, Malat zu Malat-autotroph. Die Ergebnisse sprechen für das Vorliegen von zwei Isocitrat-Dehydrogenasen, eine spezifische für NAD, die andere für NADP. Die Synthese dieser beiden Enzyme wird in verschiedener Weise reguliert.
    Notes: Summary 1. The activities of the enzymes of the tricarboxylic acid cycle (TCC) have been determined in crude cell-free extracts obtained from cells of Hydrogenomonas eutropha strain H 16 (ATCC 17 699) after growth on fructose, malate, succinate, glutamate, acetate, nutrient broth, allantoin or under autotrophic conditions. The activity of the majority of the TCC-enzymes is higher after growth on acetate, succinate or malate than in fructose or autotrophically grown cells. A repression of enzyme synthesis has been observed neither in nutrient broth nor in a fructose-glutamate medium. 2. The measurements have been extended to transition experiments on the following substrate couples: autotroph to malate, fructose to malate and reverse, autotroph to autotroph-malate, malate to malate-autotroph, considering the NAD- and NADP-specific isocitrate dehydrogenase and α-ketoglutarate dehydrogenase. The results indicated the presence of two isocitrate dehydrogenases, one specific for NAD and the other for NADP. The synthesis of both these enzymes is regulated in a different fashion.
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  • 3
    ISSN: 1432-0983
    Keywords: Glutathione ; Heavy metals ; Phytochelatins ; Fission yeast ; Cadmium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Sixty glutathione-deficient mutants (gsh −) of Schizosaccharomyces pombe have been isolated by their resistance towards the mutagen N-methyl-N′-nitro-N-nitrosoguanidine (MNNG) and their sensitivity to the heavy metal Cadmium (Cd). fifty-three mutants show glutathione contents of less than 5% compared with the wild-type. The residual glutathione contents correlate with the resistance to MNNG, with the sensitivity to Cd and with the growth rate in minimal medium. The gsh −, Cd-sensitive (Cd s) mutants also show sensitivity to other heavy metals. Wild-type strains, but not the gsh − mutants, are able to excrete the heavy metal, very likely as a sulfide-containing compound. This inability of the mutants to excrete Cd and other heavy metals causes an increase in Cd accumulation in the gsh − mutants versus the wild-type. In 60% of the mutants the glutathione deficiency is very likely due to a deficiency in the enzyme glutathione synthetase (GS), the other 40% appear to be deficient in gamma-glutamyl-cysteine synthetase (GCS).
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