Inhibitory Effect of 6-Azauracil on Purified Rabbit Liver 4-Aminobutyrate Aminotransferase

Tamaki, Nanaya; Kubo, Keiko; Aoyama, Hidenori; Funatsuka, Akimi

doi:10.1093/oxfordjournals.jbchem.a134250

Cited by 10 publications

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“…The existing set may be biased toward components of the elongation machinery, since those mutants are more likely to be tested for this phenotype. Some reports suggest that 6AU may inhibit enzymes involved in amino acid catabolism such as aminoisobutyrate-pyruvate aminotransferase, albeit at relatively high drug concentrations (25,44,45). Nevertheless, there is currently a good correlation between the inability to induce PUR5 and mutations that affect transcript elongation.…”

Section: Discussionmentioning

confidence: 99%

Saccharomyces cerevisiae Transcription Elongation Mutants Are Defective in PUR5 Induction in Response to Nucleotide Depletion

Shaw

Reines

2000

Molecular and Cellular Biology

124

163

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IMP dehydrogenase (IMPDH) is the rate-limiting enzyme in the de novo synthesis of guanine nucleotides.It is a target of therapeutically useful drugs and is implicated in the regulation of cell growth rate. In the yeast Saccharomyces cerevisiae, mutations in components of the RNA polymerase II (Pol II) transcription elongation machinery confer increased sensitivity to a drug that inhibits IMPDH, 6-azauracil (6AU), by a mechanism that is poorly understood. This phenotype is thought to reflect the need for an optimally functioning transcription machinery under conditions of lowered intracellular GTP levels. Here we show that in response to the application of IMPDH inhibitors such as 6AU, wild-type yeast strains induce transcription of PUR5, one of four genes encoding IMPDH-related enzymes. Yeast elongation mutants sensitive to 6AU, such as those with a disrupted gene encoding elongation factor SII or those containing amino acid substitutions in Pol II subunits, are defective in PUR5 induction. The inability to fully induce PUR5 correlates with mutations that effect transcription elongation since 6AU-sensitive strains deleted for genes not related to transcription elongation are competent to induce PUR5. DNA encompassing the PUR5 promoter and 5 untranslated region supports 6AU induction of a luciferase reporter gene in wild-type cells. Thus, yeast sense and respond to nucleotide depletion via a mechanism of transcriptional induction that restores nucleotides to levels required for normal growth. An optimally functioning elongation machinery is critical for this response.

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Section: Discussionmentioning

confidence: 99%

Saccharomyces cerevisiae Transcription Elongation Mutants Are Defective in PUR5 Induction in Response to Nucleotide Depletion

Shaw

Reines

2000

Molecular and Cellular Biology

124

163

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“…6-Azauracil acted as a non-competitive inhibitor for AlaAT-I with respect to j-alanine as well as 2-oxoglutarate [25] and had a Ki of approximately 0.7 mM [25]. On the other hand, 6-azauracil was also inhibitory for AlaAT-11, but the mode of action was a competitive type to a-alanine and had a Ki of 9.0 mM.…”

Section: Kinetics Of 6-azauracil Toward Alaat-iimentioning

confidence: 93%

“…The incorporation of [rnethyl-'4C]thymine into 3-aminoisobutyric acid was increased 42-fold by 6-azauracil [24]. 6-Azauracil was a noncompetitive inhibitor of purified AlaAT-I from rabbit liver [25], but the mode of action of 6-azauracil on AlaAT-I1 is obscure.…”

Section: D-3-aminoisobutyrate -Pyruvate Aminotransferase [(R)-mentioning

confidence: 99%

Purification, characterization and inhibition of d‐3‐aminoisobutyrate aminotransferase from the rat liver

Tamaki

Kaneko

Mizota

et al. 1990

European Journal of Biochemistry

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D-3-Aminoisobutyrate -pyruvate aminotransferase was purified 2000-fold from rat liver extract using heat treatment, ammonium sulfate fractionation, carboxylmethyl-Sepharose CL-6B, DEAE-Sepharose CL-6B, hydroxyapatite, Sephacryl S-200 and electrofocusing chromatographies. The purified enzyme was shown to be homogeneous by gel electrophoresis both in the presence and absence of SDS. Its molecular mass, determined by gel filtration, was 220 kDa and the subunit molecular mass was 52 kDa. The enzyme exhibited absorption maxima at 280 nm and 412 nm with a shoulder at 330 nm at neutral pH. The pH optimum for enzyme activity was 9.5 and the K, values for p-alanine and pyruvic acid were calculated to be 0.81 mM and 0.45 mM, respectively. The purified enzyme catalyzed the transamination of w-amino acids; P-alanine and D-3-aminoisobutyric acid served as good amino donors, and pyruvic acid, glyoxylic acid and oxaloacetic acid were favorable amino acceptors.6-Azauracil and 6-azathymine were found to be potent inhibitors of purified rat liver D-3-aminoisobutyratepyruvate aminotransferase. 6-Azauracil acted as a competitive inhibitor with respect to p-alanine, and was an uncompetitive inhibitor with respect to pyruvic acid with a Ki of approximately 8.9 mM.

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4-Aminobutyrate transaminase

Springer Handbook of Enzymes

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Inhibitory Effect of 6-Azauracil on Purified Rabbit Liver 4-Aminobutyrate Aminotransferase

Cited by 10 publications

References 0 publications

Saccharomyces cerevisiae Transcription Elongation Mutants Are Defective in PUR5 Induction in Response to Nucleotide Depletion

Saccharomyces cerevisiae Transcription Elongation Mutants Are Defective in PUR5 Induction in Response to Nucleotide Depletion

Purification, characterization and inhibition of d‐3‐aminoisobutyrate aminotransferase from the rat liver

4-Aminobutyrate transaminase

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