Differences in P-420 hemoproteins from untreated and 3-methylcholanthrene-treated rats.

The administration of 3-methylcholanthrene to rats leads to changes in the enzyme systems of the liver which oxidize drugs. These changes have been related to changes in some of the spectral properties of microsomal cytochrome P-450. The altered cytochrome appearing after 3-methylcholanthrene treatment has been called P,-450,’ P-448, P-446, Pa450, and high-spin P-450 by different investigators. Among the questions which have been raised are whether there is more than one molecular species of cytochrome P-450 in hepatic microsomes from untreated animals and how 3-methylcholanthrene exerts its effectby altering the relative amounts of existing cytochromes or by inducing the formation of a new cytochrome. As cytochrome P-420 is a soluble degradation product of cytochrome P-450, it was felt that changes in cytochrome P-450 induced by 3-methylcholanthrene might be reflected in cytochrome P-420 isolated from treated animals.