TABLE 3.

Kinetic parameters for cob(III)alamin and cob(II)alamin reduction by purified PduS-His6

ReactionVariable substrateKma (μM)Vmaxa (nmol min−1 mg−1)kcat (s−1)kcat/Km (μM−1 s−1)
Cob(III)alamin reductionbNADH10.1 ± 0.7(43.1 ± 0.5) × 10335.3 ± 0.43.5
OH-Cbl67.5 ± 8.2(46.6 ± 1.6) × 10338.2 ± 1.30.57
Cob(II)alamin reductioncNADH27.5 ± 2.456.8 ± 1.1(46.6 ± 0.9) × 10−31.7 × 10−3
Cob(II)alamin72.4 ± 9.564.7 ± 3.6(53.0 ± 3.0) × 10−30.7 × 10−3
  • a The values of Km and Vmax were from nonlinear regression using GraphPad Prism 5.

  • b Cob(III)alamin reduction assays were performed with 25 nM anaerobically purified PduS-His6.

  • c Cob(II)alamin reduction assays were performed with 1 μM anaerobically purified PduS-His6 protein in the presence of 0.5 mM iodoacetate.