Amino acid metabolism in the thermophilic phototroph,Chloroflexus aurantiacus: properties and metabolic role of two l-threonine (l-serine) dehydratases |
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Authors: | Gisela Laakmann-Ditges Jobst-Heinrich Klemme |
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Institution: | (1) Institut für Mikrobiologie der Universität Bonn, Meckenheimer Allee 168, D-5300 Bonn 1, Federal Republic of Germany |
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Abstract: | Two l-threonine (l-serine) dehydratases (EC 4.2.1.16) of the thermophilic phototrophic bacterium Chloroflexus aurantiacus Ok-70-fl were purified to electrophoretic homogeneity by procedures involving anion exchange and hydrophobic interaction chromatography. Only one of the two enzymes was sensitive to inhibition by l-isoleucine (K
i=2 M) and activation by l-valine. The isoleucine-insensitive dehydratase was active with l-threonine (K
m=20 mM) as well as with l-serine (K
m=10 mM) whereas the other enzyme, which displayed much higher affinity to l-threonine (K
m=1.3 mM), was inactivated when acting on l-serine. Both dehydratases contained pyridoxal-5-phosphate as cofactor. When assayed by gel filtration techniques at 20 to 25° C, the molecular weights of both enzymes were found to be 106,000±6,000. In sodium dodecylsulfate-polyacrylamide gel electrophoresis, the two dehydratases yielded only one type of subunit with a molecular weight of 55,000±3,000. The isoleucine-insensitive enzyme was subject to a glucose-mediated catabolite repression.Abbreviations A
absorbance
-
ile
isoleucine
- PLP
pyridoxal-5-phosphate
- SDS
sodium dodecyl sulfate
- TDH
threonine dehydratase
- U
unit |
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Keywords: | Serine Threonine Dehydratase Chloroflexus aurantiacus Thermophilic |
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