Genetic regulation of aryl hydrocarbon hydroxylase induction. V. Specific changes in spin state of cytochrome P 450 from genetically responsive animals.

The genetically controlled expression of hepatic aryl hydrocarbon (benzo[alpyrene) hydroxylase induction in inbred and hybrid mice by aromatic hydrocarbons in vivo is associated, in freshly prepared oxidized microsomes, with increases in high spin cytochrome P4s0 having a set of electron paramagnetic resonance signals at g = 8.0, 3.7, and 1.7. Phenobarbital causes similar rises (Zto 3-fold) in both high (g = 8.0, 3.7, and 1.7) and low spin (g = 2.4, 2.3, and 1.9) hepatic PdSO from any of the inbred or hybrid mice examined. Acetone treatment of microsomes in vifro destroys the g = 8.0, 3.7, 1.7 signals without affecting the hydroxylase activity, whereas Triton X-100 or sodium dodecyl sulfate affects the enzyme activity more so than the high spin signals. Substrate binding produces interconversion between high and low spin PdSO. In vitro treatment of microsomes with sodium dodecyl sulfate or sodium deoxycholate or at 55” for 5 min causes the irreversible loss of high and low spin signals concomitant with a rise in the g = 5.95 signal. Induction of the hydroxylase activity is associated with the increased g = 8.0,3.7, and 1.7 signal heights in the kidney from 3-methylcholanthrene-treated rabbit and in the liver or kidney from 3-methylcholanthrene-treated rat, but not in liver from aromatic hydrocarbon-treated rabbit. Hence, aryl hydrocarbon hydroxylase induction by polycyclic hydrocarbons and the increase in high-spin cytochrome P4so are not always necessarily related. These results indicate that aromatic hydrocarbon treatment of the genetically responsive animal, rather than treatment of any animal with aromatic hydrocarbons per se, causes an increase in a PGO species which has iron in a preferred high spin configuration. This preferred spin state