Abstract
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 of various inducers with Ah receptor.
Highlights
Purified P2-450, reconstituted in ular chemical is able to induce a particular P-450 protein has vitro, metabolizes acetanilide’poorly and benzo[a]py- been the centralgoal of this laboratory
Anti-(P2-450) inhibits(90 to 100%) involved the expression of mouse P2-450 induction hydrocarbonhydroxylase (PI-450), controlled by the liver microsomal isosafrole metabolite formation, yet A h receptor [6,7,8]. These studieshave alwaystaken advantage has no effect on aryl hydrocarbon hydroxylase, acetan- of the fact that theB6 mouse (Ahb/Ahb)has a large amount ilide 4-hydroxylase, biphenyl 2- or 4-hydroxylase, or of the high affinity receptor and theD2 mouse (Ahd/Ahdh) as
Following 3-methylcholanthrene cholanthrene induces anti-(P2-450)-precipitablepro- treatment, PI-450 is highly induced in B6 mouse liver tein about 12-fold in C57BL/6N and 2-foldDBinA/2N and negligibly induced in D2 mouse liver
Summary
Coumarin 0-de-ethylase [28] activities were carried out by the procedures cited. Reconstitution experiments were performed with 30 pg of dilauroylphosphatidylcholine,0.5 unit of NADPH P-450reductase, and 100 pmol of P2-450 incubated a t room temperature for 10 min; the regular buffer and assay conditions for each activity were used, according to thepreviously published techniques. Ah Receptor Assay-The postmicrosomal supernatanot f individual livers from untreated mice was exposed to 10 nM ['HITCDD (in the absence or presence of nonlabeled 1 p~ TCDD) for 1 h at 4 "C. Following dextran-charcoal adsorption, the material was centrifuged on a linear (5 to20%) sucrose density gradient,as detailed [29]. The saturable radioactivity in the Ah receptor peak was equated with femtomoles of receptorper mg of cytosolic protein and with the number of TCDD-binding sites percell [29]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
