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. Author manuscript; available in PMC: 2010 Apr 8.
Published in final edited form as: J Am Chem Soc. 2009 Apr 8;131(13):4685–4694. doi: 10.1021/ja808346y

Table 4.

Kinetic parameters for PfOPRT and HsOPRT with OMP and p-nitrophenyl β-D-ribose 5′-phosphate a.
OMP p-Nitrophenyl
β-D-ribose 5′-
phosphate		 p-Nitrophenyl
β-D-ribose
enzyme substrate kcat
(s−1)		 Km
(μM)		 kcat/Km
(M−1 s−1)		 Kib
(nM)
PfOPRT PA 0.014 ± 0.002 2.90 ± 1.09 4.8 × 103 --- ---
PPi 1.96 ± 0.29 3.73 ± 1.36 5.3 × 105 40 ± 21 188 ± 40
HsOPRT PA 0.017 ± 0.002 2.14 ± 0.61 7.9 × 103 --- ---
PPi 0.10 ± 0.01 1.55 ± 0.61 6.5 × 104 41 ± 19 121 ± 30
a

Assays were performed at 25 °C by adding purified PfOPRT or HsOPRT into mixtures containing 50 mM Tris-HCl (pH = 8.0), 5 mM MgCl2, 20 mM PA or 1 mM PPi and varied concentrations of p-nitrophenyl β-D-ribose 5′-phosphate, p-nitrophenyl β-D-ribose, OMP and PA or PPi.

b

The Ki value is for the inhibitors with respect to competitive inhibition for OMP.