The effects of
starvation on the composition of 12 different
cytochrome P450s in rat hepatic microsomes were studied with a specific antibody. Changes in the metabolic activity of the microsomes were studied at the same time. P450 DM (P450j) was induced 2.5-fold by a 48-h
starvation and its increase reflected the increase of metabolic activity of hepatic microsomes toward
aniline,
7-ethoxycoumarin, and
N-nitrosodimethylamine. P450 K-5, the major renal
cytochrome P450 in untreated male rat, was also induced 2.5-fold by a 48-h
starvation. P450 UT-2 (P450h) and P450 UT-5 (P450g), typical male-specific forms, decreased with
starvation. P450 UT-2 had high
testosterone 2 alpha- and 16 alpha-hydroxylation activities. These activities of hepatic microsomes were reduced with the decrease in P450 UT-2. P450 PB-1,
testosterone 6 beta-hydroxylase, was increased time-dependently by
starvation. P450 UT-4 (RLM2), a minor male-specific form, was not changed by
starvation. P450 PB-2 (P450k), present in both sexes, was changed little by
starvation. P450 PB-4 (P450b) and P450 PB-5 (
P450e) are strongly induced in rat liver by
phenobarbital in coordinate fashion.
Starvation increased P450 PB-4 12-fold but reduced P450 PB-5 to 22% of the control level. P450 MC-1 (P450d) was decreased by
starvation. P450 MC-5 (P450c) was barely detected in control rats and was not changed by
starvation. P450 IF-3 (P450a), rich in immature rats, was increased by
starvation, accompanied by an increase in
testosterone 7 alpha-hydroxylation activity in the hepatic microsomes. We further investigated whether new
cytochrome P450s appeared upon
starvation by comparison of chromatographic profiles of
cytochrome P450 from starved rats with those of
cytochrome P450 from control rats using HPLC. Three new
cytochrome P450s were detected in the starved rats. These
cytochrome P450s were purified to homogeneity. One of them was P450 DM, judging from spectral properties, catalytic activity, and the NH2-terminal sequence. The two other forms were designated P450 3b and 4b. The minimum molecular weights of P450 3b and 4b were 53,000 and 52,000, respectively, and their CO-reduced absorption maxima were at 449 and 452 nm, respectively. P450 3b metabolized
aminopyrine,
N-nitrosodimethylamine,
7-ethoxycoumarin, and
lauric acid, but with low activity. P450 4b was efficient in
lauric acid omega- and (omega-1)-hydroxylation only. The spectral properties, catalytic activity,
peptide map, and NH2-terminal sequence of P450 4b agreed with those of P450 K-5. P450 3b was a new
cytochrome P450, judged by these criteria.