THE FLAVOPROTEIN COMPONENT OF THE ESCHERICHIA-COLI SULFITE REDUCTASE CAN ACT AS A CYTOCHROME P450C17 REDUCTASE

The flavoprotein component (SiR-FP) of the E. coli sulfite reductase w as found to support 17 alpha-hydroxylation of pregnenolone in the pres ence of cytochrome P450c17. Half maximum activity is obtained for a 1: 1 ratio of SiR-FP, expressed as monomer concentration, to P450c17. Whe n compared to bovine NADPH-cytochrome P450 reductase, SiR-FP is about 12-15 times less efficient. P450c17 was demonstrated to interact speci fically with the FMN-binding domain of the protein and the N-terminal part of SiR-FP is suspected to play a role in electron transfer. A clu ster of negatively charged residues was found in SiR-FP by amino acid sequence comparison with rat cytochrome P450 reductase. These results argue in favour of the flavodoxin origin of the FMN-binding domain of SiR-FP. (C) 1998 Academic Press.