TABLE 2. Metabolism of NNK by heterologously expressed CYP2A13.1 and CYP2A13.2.

Incubation mixtures contained 100 mM sodium phosphate buffer, pH 7.4, 1.0 mM EDTA, 3.0 mM MgCl₂, an NADPH-generating system (5.0 mM glucose-6-phosphate, 1.0 mM NADPH, and 1.5 Units of glucose-6-phosphate dehydrogenase), 2–50 μM NNK (containing 1 μCi [5-³H]NNK), 5.0 mM sodium bisulfite, 20 or 40 pmol of purified rat CPR, and 5 or 10 pmol of CYP2A13, in a total volume of 0.4 ml. Reactions were carried out at 37°C for 5–10 min. NNK metabolites were determined using radiometric HPLC, as described in Materials and Methods. The K_m and V_max values represent means ± S.D. from three separate determinations.

Enzyme	Keto Aldehyde		Keto Alcohol
	Vmax	Km	Vmax	Km
	nmol/min/nmol P450	μM	nmol/min/nmol P450	μM
CYP2A13.1	5.1 ± 0.2	6.8 ± 1.1	2.0 ± 0.2	5.7 ± 1.6
CYP2A13.2	3.6 ± 0.1b	6.4 ± 1.0	1.1 ± 0.2a	4.7 ± 2.2

^aSignificantly different from CYP2A13.1; p<0.01

^bSignificantly different from CYP2A13.1; p<0.001