J Biol Chem. 1984 Feb 25;259(4):2675-82.  

Isosafrole-induced cytochrome P2-450 in DBA/2N mouse liver. Characterization and
genetic control of induction.

Ohyama T, Nebert DW, Negishi M.

Mouse "cytochrome P2-450" is defined as that form of isosafrole-induced P-450 in
DBA/2N liver most specifically correlated with isosafrole metabolism. Isosafrole
pretreatment does not induce aryl hydrocarbon hydroxylase activity ("cytochrome
P1-450") in C57BL/6N or DBA/2N mice, induces acetanilide 4-hydroxylase activity
("cytochrome P3-450") more than 3-fold in C57BL/6N but not in DBA/2N mice, and
induces isosafrole metabolite formation more than 3-fold in both C57BL/6N and
DBA/2N mice. P2-450 was, therefore, purified from isosafrole-treated DBA/2N
liver microsomes having negligible amounts of contaminating P1-450 and P3-450.
The apparent molecular weight of P2-450 is 55,000, and the protein appears
homogeneous on sodium dodecyl sulfate-polyacrylamide gels. The Soret peak of the
reduced purified cytochrome X CO complex is 448 nm. Purified P2-450,
reconstituted in vitro, metabolizes acetanilide poorly and benzo[a]pyrene hardly
at all. Anti-(P2-450) inhibits (90 to 100%) liver microsomal isosafrole
metabolite formation, yet has no effect on aryl hydrocarbon hydroxylase,
acetanilide 4-hydroxylase, biphenyl 2- or 4-hydroxylase, or 7-ethoxycoumarin
O-de-ethylase activities. 3-Methylcholanthrene induces
anti-(P2-450)-precipitable protein about 12-fold in C57BL/6N and 2-fold in
DBA/2N liver; 2,3,7,8-tetrachlorodibenzo-p-dioxin (10 micrograms/kg), about
12-fold in both C57BL/6N and DBA/2N liver; isosafrole, more than 3-fold in both
C57BL/6N and DBA/2N. Benzo[a]anthracene at maximal doses induces
anti-(P2-450)-precipitable protein in C57BL/6N liver no more than 2-fold, yet is
known to be a highly potent inducer of P1-450 mRNA in C57BL/6N liver. The
sensitivity of the P2-450 induction process to isosafrole is inherited as an
autosomal additive trait; studies of offspring from the C57BL/6N(DBA/N)F1 X
DBA/2N backcross confirm involvement of the Ah locus or s closely segregating
gene. In contrast, among crosses between C57BL/6N and DBA/2N, sensitivity of the
P1-450 and P3-450 induction process to 3-methylcholanthrene or
2,3,7,8-tetrachlorodibenzo-p-dioxin is inherited as an autosomal dominant trait.
These data suggest that, although P1-450, P2-450, and P3-450 proteins are
controlled by the Ah locus, either a P-450 protein polymorphism exists between
C57BL/6N and DBA/2N mice or subtle differences may exist in the interaction