Abstract
The flavoprotein component (SiR-FP) of theE. colisulfite reductase was found to support 17α-hydroxylation of pregnenolone in the presence of cytochrome P450c17. Half maximum activity is obtained for a 1:1 ratio of SiR–FP, expressed as monomer concentration, to P450c17. When compared to bovine NADPH-cytochrome P450 reductase, SiR–FP is about 12–15 times less efficient. P450c17 was demonstrated to interact specifically with the FMN-binding domain of the protein and theN-terminal part of SiR–FP is suspected to play a role in electron transfer. A cluster 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.
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