, Volume 11, Issue 3, pp 131-136

Kinetic properties of ATP phosphoribosyltransferase of escherichia coli

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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.

  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.

  2. Apparently AMP acts as a competitive inhibitor of ATP.

  3. The bisubstrate kinetics gives a pattern of parallel lines, suggesting a double displacement mechanism.

  4. The inhibition by histidine appears not to be cooperative or perhaps slightly negatively cooperative.