Introduction: Aspartate transcarbamylase (ATCase) is involved in the initial steps of
pyrimidine nucleotide biosynthesis and subject to regulation. Objective: Since Phenobarbital is an important
drug, the current study focuses on a comparative investigation of the inhibition of bacterial and
murine ATCase by some phenobarbital analogues. Methods: Phenobarbital analogues (thymidine,
phenobarbital, and thiobarbituric acid) have been subjected for in vitro and in vivo investigation of
their effect on ATCase in mice and three strains of Escherichia coli. Results: The half maximal inhibitory
concentrations (IC50) of ATCase activity were measured for each compound. According to IC50 values, an in vitro
and in vivo inhibition was obtained upon the treatment of mammalian and bacterial ATCases with the three compounds,
whereas thiobarbituric acid is the most potent among all. Its obtained IC50 values are 0.2 ± 0.045 and 0.3 ± 0.03 mM for
the bacterial and mammalian enzyme, respectively. Furthermore, the in vivo treatment of ATCase with different doses of
these compounds showed the same tendency in a dose-dependent manner. Conclusion: These observations suggest that
these inhibitors may interfere with the regulation of the enzyme and eventually lead to an additional biological effect of
phenobarbital analogues in mammals and bacteria.
Keywords: Aspartate transcarbamylase, enzyme inhibitors, thymidine, phenobarbital, thiobarbituric acid, phenobarbital analogues.
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