Weanling rats, divided into 3 groups were maintained for 15 days on a diet containing either 5 per cent casein fed ad libitum (Group 1), 20 per cent casein pair-fed to Group 1 (Group 2), or 20 per cent casein fed ad libitum (Group 3). Animals were injected with either 0.9 percent saline or phenobarbital.

Phenobarbital increased microsomal protein, cytochrome P-450, and phosphatidylcholine in all dietary groups; however, in all groups the increase in P-450 was greater than for phosphatidylcholine. Protein deficiency (Groups 1 vs. 2) decreased P-450 and microsomal protein but had no effect on phosphatidylcholine contents.

The fraction of phosphatidylcholine-associated sites relative to the total sites was greater during protein deficiency and was in agreement with a greater Δ A_max per nmole P-450 for ethylmorphine. Phenobarbital induction decreases the proposed fraction of phosphatidylcholine-associated P-450 sites relative to the total P-450 sites and results in a decrease in the Δ A_max per nmole P-450 for ethylmorphine. Phenobarbital increased the Δ A_max per mg of microsomal protein for aniline, which paralleled the increase in total P-450 indicating that the Type II site is independent of any association Of cytochrome P-450 with phosphatidylcholine. The V_max per mg of microsomal protein was 64-66 per cent lower in the protein deficient group. Equivalent reductions of cytochrome P-450 and activities of cytochrome P-450 and c reductases were observed. Phenobarbital induction increased enzyme activities (V_max per mg of microsomal protein) in all groups with greater percentage increases in the protein deficient animals.

The data suggested that phosphatidylcholine and cytochrome P-450 play important roles in the kinetics of metabolism and binding determined after protein deficiency and/or phenobarbital induction.

The dietary study was repeated using 3-methylcholanthrene as inducer. 3-methylcholanthrene produced results similar to phenobarbital in most cases; however, this inducer illicits the production of a form of P-450 termed P-448. Induction of the various parameters appears more dependent on P-448 production than phosphatidylcholine-P-450 interactions. In contrast to phenobarbital treatment, 3-methylcholanthrene treatment does not increase the specific activity for ethylmorphine metabolism and the activity of cytochrome P-450 and c reductase.

Other studies indicated the K_m and V_max for ethylmorphine N-demethylation is dependent on the substrate concentration range used to determine them. The oxidase system appears to have two different activities, one involving low substrate concentrations; the other, high substrate concentrations.

During induction by both phenobarbital and 3-methylcholanthrene, there is a depression in both K_m and V_max during the first few hours after injection of the inducer which corresponds to the time period when the inducer is in the greatest concentration in the cell. After this initial depression, there was an increase in both K_m and V_max , indicating induction had taken place.