Amino acid sequence of COOH-terminal 20K Da fragment from pig liver microsomal NADPH-cytochrome P-450 reductase

Complete structure of the hydrophilic domain in the porcine NADPH-cytochrome P-450 reductase

The 622-residue amino acid sequence of the hydrophilic domain in the porcine NADPH-cytochrome P-450 reductase (EC 1.6.2.4) is reported. The structural data required to complete the sequences published previously [Vogel, Kaiser, Witt & Lumper (1985) Biol. Chem. Hoppe-Seyler 366, 577-587] and to establish the primary structure of the porcine hydrophilic domain have been obtained by sequencing proteolytic subfragments derived from CNBr fragments and by characterizing the overlapping S-[14C]methylmethionine-containing peptides isolated from tryptic digests of the [14C]methyl-labelled hydrophilic domain. The hydrophilic domain displays 91.8% positional identity with that of the corresponding domain in the rat NADPH-cytochrome P-450 reductase. The region Val528-Ser678 in the NADPH-cytochrome P-450 reductase shows a significant homology to the sequence Ile165-Tyr314 in the spinach ferredoxin-NADP+ oxidoreductase. A model for the secondary structure of the hydrophilic domain has been derived by computer-assisted analysis of the amino acid sequence. Cys472 and Cys566 are protected against chemical modification in the NADP+ complex of the NADPH-cytochrome P-450 reductase.

Expression of rat NADPH-cytochrome P-450 reductase cDNA in Saccharomyces cerevisiae

A full-length cDNA for rat NADPH-cytochrome P-450 reductase was cloned by the procedure of Okayama and Berg (1982) from hepatic poly(A)RNA prepared from phenobarbital-induced rats. Both cDNA and amino acid sequences agreed with the sequences reported by Porter and Kasper (1985) except for four single base differences. Three expression plasmids were constructed by insertion of the reductase cDNA between yeast alcohol dehydrogenase I (ADH) promoter and terminator regions. Plasmids pARF1 and pTRF2 were constructed with slightly different lengths between the ADH promoter and the initiation codon; on introduction into Saccharomyces cerevisiae AH22 cells, they synthesized about 1 X 10(3) and 5 X 10(3) reductase protein molecules per cell, respectively. A third plasmid, pARM1, containing a cytochrome P-450MC cDNA expression unit located between two reductase cDNA expression units synthesized 4 X 10(5) cytochrome P-450MC hemoprotein and 1 X 10(4) reductase protein molecules per cell. The cellular extracts of the AH22/pARM1 strain, which synthesized both rat enzymes, showed higher cytochrome c reductase and cytochrome P-450MC-dependent 7-ethoxycoumarin O-deethylation activities as compared to extracts of the AH22/pAMC1 strain, which synthesized only rat cytochrome P-450MC. 7-Ethoxycoumarin O-deethylation activity in the cellular extract of AH22/pARM1 strain was partly inhibited by the addition of anti-rat reductase IgG. In addition, whole AH22/pARM1 cells exhibited higher monooxygenase activity toward acetanilide and 7-ethoxycoumarin than control AH22/pAMC1 cells. These results indicated that a functional electron-transport chain consisting of rat NADPH-cytochrome P-450 reductase and rat cytochrome P-450MC was constructed in S. cerevisiae cells.