TABLE 1

P450 2B6 and 2A6 content relative to the rate of nicotine 5′-oxidation by human liver microsomes



P450 Contenta

P450 Activityb
HLM Total
2B6
2A6
Coumarin 7-Hydroxylationc
(S)-Mephenytoin N-Demethylationd
Nicotine 5′-Oxidatione

5′-Iminium Ion
Cotinine
Total
Percentage Inhibition by P450 2A6 Antibody
pmol/mg pmol/min/mg
1 149 3.2 32.5 115 ± 0.43 51.3 119 ± 18.3 16.3 ± 13.2 135 ± 22.7 92
2 136 3.4 29.6 106 ± 1.7 71.0 160 ± 16.4 34.3 ± 10.5 194 ± 26.2 83
39 112 4.4 15.6 83.5 ± 0.4 13 29.3 ± 4.18 0 29.3 ± 4.18 83
129 71 0.8 16.1 98.0 ± 1.3 1.2 N.D. N.D.
130 279 3.0 58.3 491 ± 14.6 18.2 96.7 ± 4.54 5.86 ± 6.77 103 ± 11.3 90
131 179 0.9 36.8 546 ± 32.4 5.9 86.4 ± 4.60 17.7 ± 2.50 104 ± 6.69 97
132 254 1.7 46.7 183 ± 6.3 5.4 67.3 ± 10.5 24.9 ± 5.40 92.3 ± 15.2 86
133 95 0.4 17.5 122 ± 2.4 0.8 N.D. N.D.
134 109 3.9 16.1 81.0 ± 0.89 40.0 69.7 ± 8.15 8.09 ± 9.67 77.8 ± 16.7 87
141 317 1.4 48.9 423 ± 12.6 18.6 137 ± 13.5 86.9 ± 13.2 223 ± 0.85 89
HH2
146
<1f
N.D.
0.0 ± 0.0
13.8
1.5 ± 1.5
0
1.5 ± 1.5
0
  • N.D., not determined.

  • a P450 content was determined by CO difference spectra; relative P450 2A6 and 2B6 content was determined by Western blot in combination with densitometry.

  • b Values are means ± S.D.

  • c Rates were determined in the absence of cytosol, n = 4.

  • d Values were determined in the presence of sulfaphenazole, n = 2; values agreed within 10%.

  • e HLMs (0.2 mg) were incubated with [3H]nicotine (100 μM; specific activity, 0.01 μCi/nmol) for 30 min, n = 4 (n = 6 for HLM 1 and HLM HH2).

  • f Not quantified, below limit of detection.