| Abstract: | The major form of microsomal cytochrome P-450 induced by trans-stilbene oxide in the liver of male Sprague-Dawley rats was purified and characterized, and compared with the isolated cytochrome P-450 B2 forms from phenobarbital- and 3-methylcholanthrene-pretreated animals. The apparent subunit molecular weight of the trans-stilbene oxide-induced cytochrome was found to be 53 000 using sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and the absorbance maximum of the carbon monoxide complex of the ferrous cytochrome was 450 nm. Reconstitution of the N-demethylase activity towards three different substrates showed high and similar activities with the cytochrome P-450 B2 forms from trans-stilbene oxide or phenobarbital-treated rats, with one exception. Amino-acid analysis also showed a very high degree of similarity between these two forms. Upon proteinase treatment with three different proteinases the trans-stilbene oxide-induced cytochrome demonstrated in each case a peptide pattern identical to that obtained with the phenobarbital-induced B2 form. Furthermore, both forms are completely immunologically cross-reactive. We therefore conclude from these experiments that the liver microsomal P-450 B2 from trans-stilbene oxide and phenobarbital-treated rats are very closely related, if not identical. |
