Summary
The reversible reaction catalyzed by ATP phosphoribosyltransferase favors the pyrophosphorolysis of phosphoribosyl-ATP (PR-ATP). The enzyme is inhibited by PR-ATP. To avoid this problem and measure with confidence initial rates of the transferase, we have purified more than one hundred fold the enzyme PR-ATP pyrophosphohydrolase, which irreversibly converts PR-ATP to PR-AMP. Using this coupled assay, we report on substrate kinetics and histidine inhibition studies of ATP phosphoribosyltransferase ofEscherichia coli.
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1.
In the absence of histidine the variation of initial velocity as a function of ATP or phosphoribosyl pyrophosphate (PRPP) concentration, follows Michaelis-Menten kinetics, with ATP inhibiting at high concentrations. In the presence of histidine a change from hyperbolic to sigmoidal kinetics is observed.
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2.
Apparently AMP acts as a competitive inhibitor of ATP.
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3.
The bisubstrate kinetics gives a pattern of parallel lines, suggesting a double displacement mechanism.
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4.
The inhibition by histidine appears not to be cooperative or perhaps slightly negatively cooperative.
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Tébar, A.R., Ballesteros, A.O. Kinetic properties of ATP phosphoribosyltransferase of escherichia coli. Mol Cell Biochem 11, 131–136 (1976). https://doi.org/10.1007/BF01744993
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DOI: https://doi.org/10.1007/BF01744993