TABLE 3. Metabolism of NNK by heterologously expressed CYP2A13.1 and CYP2A13.2 with varying amounts of CPR.

Contents of incubation mixtures were the same as described in the legend of Table 2, except that 10 μM NNK (containing 1 μCi [5-³H]NNK), 5, 10, or 30 pmol of rat CPR, and 5 or 10 pmol of CYP2A13, were used. Reactions were carried out at 37°C for 10 min. Data represent the average of two determinations; individual values varied by <15% of the mean.

Enzymes	Rate of keto aldehyde formation (nmol/min/nmol P450)
	CYP/CPR molar ratio	1:3	1:1	2:1
10 pmol CYP2A13.1 (a)		2.2	1.2	0.7
10 pmol CYP2A13.2 (b)		1.5	0.9	0.5
5 pmol CYP2A13.1		1.9	1.0	0.6
+ 5 pmol CYP2A13.2
Calculated value [(a+b)/2]		1.9	1.1	0.6