TABLE 3.

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

Reaction	Variable substrate	Kma (μM)	Vmaxa (nmol min−1 mg−1)	kcat (s−1)	kcat/Km (μM−1 s−1)
Cob(III)alamin reductionb	NADH	10.1 ± 0.7	(43.1 ± 0.5) × 103	35.3 ± 0.4	3.5
	OH-Cbl	67.5 ± 8.2	(46.6 ± 1.6) × 103	38.2 ± 1.3	0.57
Cob(II)alamin reductionc	NADH	27.5 ± 2.4	56.8 ± 1.1	(46.6 ± 0.9) × 10−3	1.7 × 10−3
	Cob(II)alamin	72.4 ± 9.5	64.7 ± 3.6	(53.0 ± 3.0) × 10−3	0.7 × 10−3

^aThe values of K_m and V_max were from nonlinear regression using GraphPad Prism 5.

^bCob(III)alamin reduction assays were performed with 25 nM anaerobically purified PduS-His₆.

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