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  • 1
    ISSN: 1432-072X
    Keywords: Archaea ; Methanogenic bacteria ; Hyperthermophiles ; Sulfate reducers ; Methanobacterium thermoautotrophicum ; Methanosarcina barkeri ; Tetrahydromethanopterin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Archaeoglobus fulgidus and Methanopyrus kandleri are both extremely thermophilic Archaea with a growth temperature optimum at 83°C and 98°C, respectively. Both Archaea contain an active N 5,N 10-methenyltetrahydromethanopterin cyclohydrolase. The enzyme from M. kandleri has recently been characterized. We describe here the purification and properties of the enzyme from A. fulgidus. The cyclohydrolase from A. fulgidus was purified 180-fold to apparent homogeneity and its properties were compared with those recently published for the cyclohydrolase from M. kandleri. The two cytoplasmic enzymes were found to have very similar molecular and catalytic properties. They differed, however, significantly with respect of the effect of K2HPO4 and of other salts on the activity and the stability. The cyclohydrolase from A. fulgidus required relatively high concentrations of K2HPO4 (1 M) for optimal thermostability at 90°C but did not require salts for activity. Vice versa, the enzyme from M. kandleri was dependent on high K2HPO4 concentrations (1.5 M) for optimal activity but not for thermostability. Thus the activity and structural stability of the two thermophilic enzymes depend in a completely different way on the concentration of inorganic salts. The molecular basis for these differences are discussed.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-072X
    Keywords: Archaea ; Methanogens ; Sulfate reducers ; Tetrahydromethanopterin ; Methanofuran ; Coenzyme F420 ; C1-Enzymes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The sulfate-reducing Archaeoglobus fulgidus contains a number of enzymes previously thought to be unique for methanogenic Archaea. The purification and properties of two of these enzymes, of formylmethanofuran: tetrahydromethanopterin formyltransferase and of N 5,N 10-methylenetetrahydromethanopterin dehydrogenase (coenzyme F420 dependent) are described here. A comparison of the N-terminal amino acid sequences and of other molecular properties with those of the respective enzymes from three methanogenic Archaea revealed a high degree of similarity.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 34 (1996), S. 3173-3181 
    ISSN: 0887-624X
    Keywords: macromonomer ; core/shell latexes ; interphase ; compatibilizing agent ; NMR relaxation studies ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In this work poly(methyl methacrylate) (PMMA) macromonomer is used as a compatibilizing agent in a poly(butyl acrylate) (PBA)/PMMA core/shell latex system. The incorporation of the PMMA macromonomer was achieved by copolymerizing it with BA monomer using miniemulsion polymerization. PBA seed latex was also synthesized without the macromonomer present to compare the compatibilizing effects with the PMMA macromonomer. The second stage methyl methacrylate monomer was added semi-continuously to the PBA seed latexes under monomer-starved conditions. Solid-state 13C-NMR [H]T1ρ relaxation studies were used to determine the effect of PMMA compatibilizer on these PBA/PMMA core/shell latex interphase regions. The thickness of the interphase of the core/shell particles prepared with and without the PMMA macromonomer compatibilizing agent are calculated to be in the range of 15-16 nm and 10-12 nm, respectively. Electron microscopy revealed that the seed latex prepared with the PMMA macromonomer achieved a more uniform coverage with the second stage PMMA polymer as compared to the latex synthesized without the compatibilizing agent present. It is concluded that the PMMA macromonomer is effective in increasing the thickness of the interphase region and also the amount of interfacial PMMA. © 1996 John Wiley & Sons, Inc.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 34 (1996), S. 3183-3190 
    ISSN: 0887-624X
    Keywords: macromonomer ; core/shell latexes ; interphase ; compatibilizing agent ; NMR relaxation studies ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In this work poly(methyl methacrylate) (PMMA) macromonomer is used as a compatibilizing agent in a poly(butyl acrylate) (PBA)/PMMA core/shell latex system. The incorporation of the PMMA macromonomer was achieved by copolymerizing it with BA monomer using miniemulsion polymerization. PBA seed latex was also synthesized without the macromonomer present to compare the compatibilizing effects with the PMMA macromonomer. The second stage methyl methacrylate monomer was added semi-continuously to the PBA seed latexes under monomer-starved conditions. Solid-state 13C-NMR [H]T1ρ relaxation studies were used to determine the effect of PMMA compatibilizer on these PBA/PMMA core/shell latex interphase regions. The thickness of the interphase of the core/shell particles prepared with and without the PMMA macromonomer compatibilizing agent are calculated to be in the range of 15-16 nm and 10-12 nm, respectively. Electron microscopy revealed that the seed latex prepared with the PMMA macromonomer achieved a more uniform coverage with the second stage PMMA polymer as compared to the latex synthesized without the compatibilizing agent present. It is concluded that the PMMA macromonomer is effective in increasing the thickness of the interphase region and also the amount of interfacial PMMA. © 1996 John Wiley & Sons, Inc.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
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