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  • 1
    Electronic Resource
    Electronic Resource
    Methylobacterium rhodesianum MB 126 possesses two acetoacetyl-CoA reductases (1994)
    Springer
    Archives of microbiology 161 (1994), S. 277-280 
    Details
    ISSN: 1432-072X
    Keywords: Poly-β-hydroxybutyrate ; Acetoacetyl-CoA reductase ; Methylotroph ; Methylobacterium rhodesianum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Two constitutive acetoacetyl-CoA (AcAc-CoA) reductases were purified from Methylobacterium rhodesianum MB 126, an NADPH-linked d(-)-β-hydroxybutyryl-CoA forming reductase (enzyme A) and an NADH-and NADPH-linked l(+)-β-hydroxybutyryl-CoA forming reductase (enzyme B). Enzyme A and B give apparent K m values of 15 μM and 30 μM for AcAc-CoA, 18 μM for NADPH and 30 μM for NADH, respectively. They are inhibited by AcAc-CoA at concentrations higher than 25 μM and 50 μM, respectively. The contribution of the two reductases to poly-β-hydroxybutyrate synthesis is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00248705
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  • 2
    Electronic Resource
    Electronic Resource
    Competition between β-ketothiolase and citrate synthase during poly(β-hydroxybutyrate) synthesis in Methylobacterium rhodesianum (1997)
    Springer
    Archives of microbiology 166 (1997), S. 405-410 
    Details
    ISSN: 1432-072X
    Keywords: Key words Poly(β-hydroxybutyrate) ; Citrate synthase ; β-Ketothiolase ; Metabolite concentrations ; Methylotroph ; Methylobacterium rhodesianum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The enzymes β-ketothiolase and citrate synthase from the facultatively methylotrophic Methylobacterium rhodesianum MB 126, which uses the serine pathway, were purified and characterized. The β-ketothiolase had a relatively high K m for acetyl-CoA (0.5 mM) and was strongly inhibited by CoA (K i 0.02 mM). The citrate synthase had a much higher affinity for acetyl-CoA (K m 0.07 mM) and was significantly inhibited by NADH (K i 0.15 mM). The intracellular concentration of CoA metabolites and nucleotides was determined in M. rhodesianum MB 126 during growth on methanol. The level of CoA decreased from about 0.6 nmol (mg dry mass)–1 during growth to the detection limit when poly(β-hydroxybutyrate) (PHB) accumulated. Nearly unchanged intracellular concentrations of NADH, NADPH, and acetyl-CoA of about 0.5, 0.6–0.7, and 1.0 nmol (mg dry mass)–1, respectively, were determined during growth and PHB synthesis. During growth, the β-ketothiolase was almost completely inhibited by CoA, and acetyl-CoA was principally consumed by the citrate synthase. During PHB accumulation, the β-ketothiolase had about 75% of its maximum activity and showed much higher activity than citrate synthase, which at the actual NADH concentration was about 75% inhibited. NADPH concentration was sufficiently high to allow the unlimited activity of acetoacetyl-CoA reductase (K m NADPH 18 μM). PHB synthesis is probably mainly controlled by the CoA concentration in M. rhodesianum MB 126.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01682987
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  • 3
    Electronic Resource
    Electronic Resource
    Regulation of poly(β-hydroxybutyrate) synthesis in Methylobacterium rhodesianum MB 126 growing on methanol or fructose (1998)
    Springer
    Archives of microbiology 169 (1998), S. 360-363 
    Details
    ISSN: 1432-072X
    Keywords: Key words Poly(β-hydroxybutyrate) ; Methylobacterium rhodesianum ; Fructose ; Regulation ; Intracellular metabolites
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The intracellular concentration of CoA metabolites and nucleotides was determined in batch cultures of Methylobacterium rhodesianum grown on methanol and shifted to growth on fructose. The intracellular concentration of CoA decreased from a high value of 0.6 nmol/mg poly(β-hydroxybutyrate)-free bacterial dry mass during growth on methanol to a low value of 0.03 nmol/mg poly(β-hydroxybutyrate)-free bacterial dry mass after a shift to fructose as a carbon source. The levels of NADH, NADPH, and acetyl-CoA were also lower. Under these conditions, acetyl-CoA was metabolized by both citrate synthase and β-ketothiolase, and poly(β-hydroxybutyrate) synthesis and growth occurred simultaneously during growth on fructose. Moreover, the level of ATP was approximately 50% lower during growth on fructose, supporting the hypothesis of a bottleneck in the energy supply during the growth of M. rhodesianum with fructose.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002030050583
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  • 4
    Electronic Resource
    Electronic Resource
    Methylobacterium rhodesianum MB 126 possesses two acetoacetyl-CoA reductases (1994)
    Springer
    Archives of microbiology 161 (1994), S. 277-280 
    Details
    ISSN: 1432-072X
    Keywords: Key words: Poly-β-hydroxybutyrate – Acetoacetyl-CoA reductase – Methylotroph –Methylobacterium rhodesianum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract. Two constitutive acetoacetyl-CoA (AcAc-CoA) reductases were purified from Methylobacterium rhodesianum MB 126, an NADPH-linked d(−)-β-hydroxybutyryl-CoA forming reductase (enzyme A) and an NADH- and NADPH-linked l(+)-β-hydroxybutyryl-CoA forming reductase (enzyme B). Enzyme A and B give apparent K m values of 15 µM and 30 µM for AcAc-CoA, 18 µM for NADPH and 30 µM for NADH, respectively. They are inhibited by AcAc-CoA at concentrations higher than 25 µM and 50 µM, respectively. The contribution of the two reductases to poly-β-hydroxybutyrate synthesis is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00248705
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  • 5
    Electronic Resource
    Electronic Resource
    Improvement of growth yield of yeast on glucose to the maximum by using an additional energy source (1983)
    Springer
    Archives of microbiology 136 (1983), S. 203-208 
    Details
    ISSN: 1432-072X
    Keywords: Maximum growth yield ; Mixed substrate utilization ; Glucose ; Formate ; Transient-state cultivation ; Hansenula polymorpha
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The experimentally determined growth yield on glucose under aerobic conditions is approximately 0.5 g/g, but on the basis of the carbon content a value of 0.71 g/g should be the upper limit if carbon conversion is improved by the use of an additional energy source. This assumption was investigated with the methylotrophic yeast Hansenula polymorpha MH 20. Formate served as an additional energy source. The growth yield experiments were performed with a transient-state fermentation technique in which formate was fed via an increasing concentration gradient to a culture growing continuously on glucose. As a result the growth yield on glucose was improve, the extent was dependent on the formate feeding rate, i.e. the slope of this formate gradient. The predicted maximum growth yield of 0.7 g/g was obtained at a slope of the formate gradient of 0.21 g/l·h at a glucose concentration of about 1 g/l. Steeper gradients did not further improve this value, but rather impaired the growth yield due to the appearence of a high residual formate concentration in the fermentation medium. The yield patterns are influenced by the culture pH, a value of at least 4.8 is necessary to achieve the maximum growth yield on glucose. At lower pH formate became increasingly toxic. The ratio of formate to glucose necessary to obtain the maximum yield coefficient was 1...1.6:1 (in grams). On the basis of the energy content of formate a ratio of 1.2...1 (P/O=2) was calculated to substitute the part of glucose which is endoxidized for energy generation. Deviations from this value are explained in terms of the manner of uptake and uncoupling property of formic acid/formate and the existence of a second, formate-“wasting” enzyme.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00409845
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  • 6
    Electronic Resource
    Electronic Resource
    Flow of 14C-methanol via assimilatory and dissimilatory sequences with yeast in presence of glucose (1985)
    Springer
    Archives of microbiology 143 (1985), S. 77-81 
    Details
    ISSN: 1432-072X
    Keywords: Mixed substrate utilization ; 14C-Methanol glucose ; Efficiency of methanol dissimilation ; Improvement of growth yield ; Hansenula polymorpha
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Experiments were performed to reveal the extent to which individual heterotrophic substrates of a mixture contribute to the overall carbon and energy metabolism. For this reason Hansenula polymorpha MH 20 was chemostatically (C-limited) cultivated at different growth rates on mixtures of methanol and glucose fed at proportions of 3:1 and 1:3 (in weight units), respectively. The distributions of 14C-carbon from methanol in biomass as well as carbon dioxide (and supernatant) fractions were determined. From these results it followed, firstly, that energy derived from methanol dissimilation was used in part for the incorporation of glucose carbon, resulting in carbon conversion efficiencies for this substrate equivalent to yield coefficients of 0.61–0.69 g/g. Secondly, the growth yield data revealed that the efficiency of methanol conversion had to be increased in order to account for the experimentally determined yield figures. This was further confirmed by theoretical treatment of the growth yield data which showed that these could only be obtained if P/O-quotients for methanol conversion similar to those for glucose, i.e. 2.0–2.5, were considered. The latter property was regarded as the main reason for the observed improvement of growth yield accompanying the simultaneous utilization of methanol and glucose in this yeast.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00414772
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  • 7
    Electronic Resource
    Electronic Resource
    Glucose as an energy donor in acetate growing Acinetobacter calcoaceticus (1986)
    Springer
    Archives of microbiology 144 (1986), S. 62-66 
    Details
    ISSN: 1432-072X
    Keywords: Acinetobacter calcoaceticus ; Continuous cultivation ; Acetate growth ; Glucose oxidation ; Energy gain ; Maximum carbon conversion efficiency
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Since glucose can be oxidized but not assimilated by Acinetobacter calcoaceticus 69-V the question arose whether energy generated by glucose oxidation can help incorporate carbon from heterotrophic substrates and, if so, what the efficiency of ATP production is like. For this reason this species was grown in the chemostat on acetate. After having reached steady state conditions an increasing concentration of glucose was added. This led to an increase in the biomass level from about 0.4 g/g for growth on acetate alone to 0.6–0.65 g/g in the presence of glucose, independently of either the growth rate or the steepness of the glucose gradient used. This upper value approximates about the limit of the carbon conversion efficiency calculated for non-glycolytic substrates. Glucose was almost exclusively oxidized to gluconic acid, 2- and 5-ketogluconates, and pentose 5-phosphates were found only in traces. These results demonstrate that glucose functions as an additional energy source in Acinetobacter calcoaceticus 69-V. From the transient behaviour of biomass increase and the mixing proportion at which the maximum growth yield on acetate in the presence of glucose was obtained it followed that two mol of ATP must have been generated per mol of glucose oxidized. This property is discussed in terms of coupling glucose dehydrogenase with the respiratory chain.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00454957
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  • 8
    Electronic Resource
    Electronic Resource
    Competition between β-ketothiolase and citrate synthase during poly(β-hydroxybutyrate) synthesis inMethylobacterium rhodesianum (1996)
    Springer
    Archives of microbiology 166 (1996), S. 405-410 
    Details
    ISSN: 1432-072X
    Keywords: Poly(β-hydroxybutyrate) ; Citrate synthase ; β-Ketothiolase ; Metabolite concentrations ; Methylotroph ; Methylobacterium rhodesianum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The enzymes β-ketothiolase and citrate synthase from the facultatively methylotrophicMethylobacterium rhodesianum MB 126, which uses the serine pathway, were purified and characterized. The β-ketothiolase had a relatively highK m for acetyl-CoA (0.5 mM) and was strongly inhibited by CoA (K i 0.02 mM). The citrate synthase had a much higher affinity for acetyl-CoA (K m 0.07 mM) and was significantly inhibited by NADH (K i 0.15 mM). The intracellular concentration of CoA metabolites and nucleotides was determined inM. rhodesianum MB 126 during growth on methanol. The level of CoA decreased from about 0.6 nmol (mg dry mass)-1 during growth to the detection limit when poly(β-hydroxybutyrate) (PHB) accumulated. Nearly unchanged intracellular concentrations of NADH, NADPH, and acetyl-CoA of about 0.5, 0.6–0.7, and 1.0 nmol (mg dry mass)-1, respectively, were determined during growth and PHB synthesis. During growth, the β-ketothiolase was almost completely inhibited by CoA, and acetyl-CoA was principally consumed by the citrate synthase. During PHB accumulation, the β-ketothiolase had about 75% of its maximum activity and showed much higher activity than citrate synthase, which at the actual NADH concentration was about 75% inhibited. NADPH concentration was sufficiently high to allow the unlimited activity of acetoacetyl-CoA reductase (K mNADPH 18 μM). PHB synthesis is probably mainly controlled by the CoA concentration inM. rhodesianum MB 126.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01682987
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  • 9
    Electronic Resource
    Electronic Resource
    The growth rate-limiting reaction in methanol-assimilating yeasts (1990)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 87 (1990), S. 0 
    Details
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract The maximum growth rate of methylotrophic yeasts during growth on methanol is about 0.2 h−1. Since they are able to grow faster on substrates such as glucose we tried to identify the putative limiting step in methanol metabolism within the assimilatory pathway, leading to the formation of a major precursor for biosyntheses, or within the linear dissimilatory sequence. Growth experiments with mixed substrates and determination of some kinetic parameters allowed us to restrict the number of possible pacemaker enzymes. The dissimilatory sequence does not seem to be growth-rate limiting. This also applies to transketolase, transaldolase and fructose-1,6-bisphosphatase. Surprisingly, methanol oxidase appears to be the prime candidate.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1574-6968.1990.tb04922.x
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  • 10
    Electronic Resource
    Electronic Resource
    Pecularities of methylotrophs concerning overflow metabolism, especially the synthesis of polyhydroxyalkanoates (1992)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 103 (1992), S. 0 
    Details
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract The accumulation of poly-β-hydroxybutyrate (PHB) is widespread in prokaryotes. The synthesis of PHB is independent of the carbon source and type of nutrition. Methylotrophic bacteria can synthesize PHB, and poly-hydroxyalkanoates (PHA), too, if suitable mixed substrates are used. Apart from the genetic disposition, the capability of accumulating PHB seems to be correlated with the serine pathway, as the synthesis of exopolysaccharides is probably coupled with the hexulosephosphate pathway. This capability prevents the obviously NADH-limited ‘serine pathway (bacteria)’ from wasting NADH, which could be due to the high capacity of the dissimilatory sequence. Provided ‘RMP bacteria’ were able to synthesize PHB, methanol differs from other substrates insofar as the synthesis can be associated with a supply or consumption of reducing equivalents. The synthesis of PHB from acetate is also energy- and reducing power-consuming. In this respect, and concerning the role of the TCA cycle, methanol and acetate resemble each other and jointly differ from glucose. That PHB syntheses from different substrates can be energy-consuming or -generating, opens up chance for improving efficiency. The prescription for this is provided by the mixed or auxiliary substrate concept. By choosing suitable substrates it is possible to enhance the carbon conversion efficiency, and in addition, to synthesize heteropolyesters.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1574-6968.1992.tb05831.x
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