Effects of Phenobarbital, 3-Methylcholanthrene, and Hematin on the Synthesis of Protein Components of Rat Liver Microsomal Membranes

Smooth endoplasmic reticulum was solubilized in sodium dodecyl sulfate and the protein components were fractionated by acrylamide gel electrophoresis. The relative rates of amino acid incorporation into the fractionated protein bands following various drug treatments were measured. The drugs used were phenobarbital and 3-methylcholanthrene, representative of two classes of drugs which induce a variety of microsomal drug-metabolizing activities, and hematin, which causes a decrease in the activities of enzymes associated with drug metabolism. Each of the three compounds produced distinctive changes in amino acid incorporation into the protein components of smooth endoplasmic reticulum. In each case the greatest change in amino acid incorporation was in a major protein band in the 50,000 molecular weight region of the gel. Cytochrome P-420, the solubilized form of cytochrome P-450, was purified and shown to migrate as a protein with a molecular weight of 50,000, indicating that this protein is contained in the 50,000 molecular weight band. Amino acid incorporation into isolated cytochrome P-420 showed that this protein is responsible for at least part of the drug-mediated changes in amino acid incorporation observed for the 50,000 molecular weight protein band.