Multiple, immunoidentical forms of phenobarbital-induced rat liver cytochromes P-450 are encoded by different mRNAs

It was shown previously that four immunochemically identified forms of phenobarbital-induced hepatic cytochromic P-450 exist in unique combinations which characterize different strains and colonies of rats. One colony of Long-Evans rats exhibited only cytochromes P-450b(LE) and P-450e among these immunorelated enzymes; whereas, one colony of Holtzman rats was characterized by cytochromes P-450b(H) and P-450e. After phenobarbital treatment, hepatic poly(A)⁺-mRNA was isolated from these groups of rats and translated in vitro. The ³⁵S-labeled products were immunoisolated with antibody to cytochrome P-450b(LE) and analyzed by two-dimensional gel electrophoresis. The results indicated that the products synthesized in vitro correspond exactly to the two particular forms of the enzyme that characterize liver microsomes from each of these groups of rats. It is concluded that different structural genes encode these immunorelated forms of cytochrome P-450 and that significant post-translational processing of their polypeptide products does not occur in vivo.