Studies on the cosubstrate site of protease solubilized NADPH-cytochrome P450 reductase

The cosubstrate NADP(H) protects lysine 601 in the porcine NADPH-cytochrome P-450 reductase against pyridoxylation

Lys601 in NADPH-cytochrome P-450 reductase is modified by reductive alkylation with pyridoxal 5'-phosphate (pyridoxylation). Lys601 is protected against modification by the cosubstrate NADP(H).

Structural comparison between the trout and mammalian hydrophilic domain of NADPH-cytochrome P-450 reductase

The isolation of the protease-solubilized NADPH-cytochrome P-450 reductase from trout liver and its properties are described. The sequence of the "hydrophilic domain" [protease-solubilized NADPH-cytochrome P-450 reductase from trout (residues Lys56-Ser678)] is reported. The CNBr fragments of the trout "hydrophilic domain" and their proteolytic subpeptides were sequenced. The CNBr fragments were aligned by homology to the reported sequence of the porcine NADPH-cytochrome P-450 reductase. The structures of the mammalian and the trout NADPH-cytochrome P-450 reductases were compared. Stretches with high exchange rates between the pig and trout reductase were found at the NH2 and the COOH terminal regions of the hydrophilic domain.

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.

Fluorescence labelling of NADPH-cytochrome P-450 reductase with the monobromomethyl derivative of syn-9,10-dioxabimane

The kinetics of thiol-group alkylation in NADPH-cytochrome P-450 reductase during its inactivation by monobromobimane has been studied using the fluorimetric determination of S-bimane-L-cysteine by high-performance liquid chromatography. Loss of activity during the reaction of NADPH-cytochrome P-450 reductase with monobromobimane is caused by the alkylation of one single critical cysteine residue, which can be protected against thiol-specific reagents by NADP(H). The chemical stability of the bimane group allows the digestion of bimane-labelled NADPH-cytochrome P-450 reductase by CNBr. The critical cysteine residue could be located in a CNBr-cleaved peptide purified to homogeneity with Mr 10 500 +/- 1 000 and valine as N-terminus.