Occurrence of two l-threonine (l-serine) dehydratases in the thermophile Chloroflexus aurantiacus

Laakmann-Ditges, Gisela; Klemme, Jobst-Heinrich

doi:10.1007/bf00410950

Cited by 13 publications

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“…The initial step is a pelimination of water followed by tautomerization and hydrolysis to pyruvate and ammonia [l]. L-Serine dehydratases as well as the related threonine dehydratases are ubiquitous enzymes found in high amounts in mammalian liver [2], Saccharomyces cerevisiae [3,4] and in a variety of eubacteria such as Escherichia coli (three different types; for a review see [5]) [6, 71,, Chloroflexus uurantiacus [9] and several lactic acid bacteria [lo]. It has been shown for most of these enzymes that they contain pyridoxal phosphate (for a review see [l 11) bound to a specific lysine residue via a Schiff base [12].…”

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confidence: 99%

Purification and properties of an iron‐sulfur‐containing and pyridoxal‐phosphate‐independent l‐Serine dehydratase from Peptostreptococcus asaccharolyticus

Grabowski

Buckel

1991

European Journal of Biochemistry

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L-Serine dehydratase with a specific activity of 15 nkat/mg protein was present in the anaerobic eubacterium Peptostreptococcus asaccharolyticus grown either on L-glutamate or L-serine. The enzyme was highly specific for L-serine with the lowest K , = 0.8 mM ever reported for an L-serine dehydratase. L-Threonine (K, = 22 mM) was the only other substrate. V/K, for L-serine was 500 times higher than that for L-threonine. L-Cysteine was the best inhibitor (Ki = 0.3 mM, competitive towards L-serine). The enzyme was purified 400-fold to homogeneity under anaerobic conditions (specific activity 6 pkat/mg). PAGE in the presence of SDS revealed two subunits with similar intensities (a, 30 kDa; p, 25 kDa). The molecular mass of the native enzyme was estimated as 200 20 kDa (gel filtration) and 180 kDa (gradient PAGE). In the absence of oxygen the enzyme was moderately stable even in the presence of sodium borohydride or phenylhydrazine ( 5 mM each). However, by exposure t o air the activity was lost, especially when the latter agent was added. The enzyme was reactivated by ferrous ion under anaerobic conditions. The inability of several nucleophilic agents to inactivate the enzyme indicated the absence of pyridoxal phosphate. This was confirmed by a microbiological determination of pyridoxal phosphate. However, the enzyme contained 3.8 f 0.2 mol Fe and 5.6 0.3 mol inorganic sulfur/mol heterodimer (55 kDa) indicating the presence of an [Fe-S] center. The enzyme was successfully applied to measure L-serine concentrations in bacterial media and in human sera.The enzyme L-serine dehydratase catalyzes the overall deamination of L-serine to pyruvate. The initial step is a pelimination of water followed by tautomerization and hydrolysis to pyruvate and ammonia [l]. L-Serine dehydratases as well as the related threonine dehydratases are ubiquitous enzymes found in high amounts in mammalian liver [2], Saccharomyces cerevisiae [3,4] and in a variety of eubacteria such as Escherichia coli (three different types; for a review see [5]) [6, 71,, Chloroflexus uurantiacus [9] and several lactic acid bacteria [lo]. It has been shown for most of these enzymes that they contain pyridoxal phosphate (for a review see [l 11) bound to a specific lysine residue via a Schiff base [12]. The amino acid sequences around this lysine residue in E. coli, yeast, rat and man are conserved [I, 3, 131. During catalysis the electron-withdrawing prosthetic group forms a new Schiff base with the substrate whereby the removal of the proton from the a-carbon of the hydroxy amino acid is facilitated [14, 151.

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Purification and properties of an iron‐sulfur‐containing and pyridoxal‐phosphate‐independent l‐Serine dehydratase from Peptostreptococcus asaccharolyticus

Grabowski

Buckel

1991

European Journal of Biochemistry

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“…However, Chloroflexus is not extremely thermophilic and there is evidence for allosteric control as a general regulatory phenomenon in several other thermophiles [15]. In addition, studies of one of the two threonine dehydratases which occur in Chloroflexus have shown that a tetrameric ('large') form of this enzyme can exist stably at temperatures above 45 °C [16,17]. These considerations suggest that high growth temperatures alone cannot explain the regulatory features of the Chloroflexus CS.…”

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confidence: 99%

Gram-positive type citrate synthase in the thermophilic green gliding bacterium Chloroflexus aurantiacus

Kelly¹

1988

FEMS Microbiology Letters

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Some properties of the citrate synthase from Chloroflexus aurantiacus have been examined in crude cell‐free extracts and partially purified preparations. The enzyme had an approximate native molecular size of 140 000, was not inhibited by NADH or 2‐oxoglutarate but was inhibited by ATP (about 50% at 5 mM). The Km for acetyl CoA at pH 8.2 in the presence of 0.5 mM oxaloacetate was determined to be 25 μM. These properties are characteristic of the ‘small’ size class of citrate synthases normally associated with gram‐positive eubacteria, despite the fact that Chloroflexus stains gram‐negatively.

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Taxonomy and Physiology of Filamentous Anoxygenic Phototrophs

Pierson

Castenholz

Advances in Photosynthesis and Respiration

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Occurrence of two l-threonine (l-serine) dehydratases in the thermophile Chloroflexus aurantiacus

Cited by 13 publications

References 15 publications

Purification and properties of an iron‐sulfur‐containing and pyridoxal‐phosphate‐independent l‐Serine dehydratase from Peptostreptococcus asaccharolyticus

Purification and properties of an iron‐sulfur‐containing and pyridoxal‐phosphate‐independent l‐Serine dehydratase from Peptostreptococcus asaccharolyticus

Gram-positive type citrate synthase in the thermophilic green gliding bacterium Chloroflexus aurantiacus

Taxonomy and Physiology of Filamentous Anoxygenic Phototrophs

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