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  • 1
    ISSN: 1432-072X
    Keywords: Methanobacterium thermoautotrophicum ; Cyclic 2,3-diphosphoglycerate ; 2,3-Diphosphoglycerate ; Cyclic 2,3-diphosphoglycerate synthetase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The levels of cyclic 2,3-diphosphoglycerate (cDPG) in methanogenic bacteria are governed by the antagonistic activities of cDPG synthetase and cDPG hydrolase. In this paper we focus on the synthetase from Methanobacterium thermoautotrophicum. The cytoplasmic 150 kDa enzyme catalyzed cDPG synthesis from 2,3-diphosphoglycerate (apparent Km=21 mM), Mg2+ (Km=3.1 mM) and ATP (Km=1–2 mM). In batch-fed cultures, the enzyme was constitutively present (6–6.5 nmol per min per mg protein) during the different growth phases. In continuous cultures, activity decreased in response to phosphate limitation. The synthetase reaction proceeded with maximal rate at pH 6 and at 65° C and was specifically dependent on high (〉0.3M) K+ concentrations. The reaction conditions remarkably contrasted to those of cDPG degradation catalyzed by the previously described membrane-bound cDPG hydrolase.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-072X
    Keywords: Methanobacterium thermoautotrophicum ; Activation ; Corrinoid enzyme ; Methyltransferase ; Methanopterin ; Coenzyme M
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The enzymatic conversion of formaldehyde to CH3S-CoM in crude extracts of Methanobacterium thermoautotrophicum was used as a means to investigate the methyl-tetrahydromethanopterin: HS-CoM methyltransferase reaction. All components necessary for formaldehyde conversion were shown to be present in a soluble protein fraction. This soluble cell fraction still contained a major amount of corrinoids. Apart from tetrahydromethanopterin no other soluble cofactors were required for formaldehyde conversion. The dependence of the system on catalytic amounts of ATP was shown to be specific. Several nucleoside triphosphates or ADP were unable to substitute for ATP. Remarkably, various strong reducing systems, especially titanium(III)citrate could replace ATP to a large extent. The ATP-dependent formaldehyde conversion to CH3S-CoM was inhibited in the presence of nitrous oxide, detergents or 2′,3′-dialdehyde-ATP. The results support a role for a corrinoid protein in the methyl-tetrahydromethanopterin: HS-CoM methyltransferase reaction at which ATP is involved in the activation of this protein, probably in the conversion of inactive B12a or B12r to active B12s.
    Type of Medium: Electronic Resource
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