Cytochrome P450 cam: SS- dimer and -SH derivative reactivities.

N-ethyl-maleimide alkylation converts ferric P450_cam to a (succinimido-cys)₄ protein with native optical and EPR spectra but insensitive to substrate induced shift of iron to high spin with Soret absorption to higher energy and inactive in putidaredoxin ferric-ferrous reduction. On photo or chemical reduction the ferrous protein oxygenates and, with reduced putidaredoxin, converts substrate to product. Mild oxidation of P450_cam yields a disulfide dimer whose properties on alkylation of 3 sulfhydryls equal the succinimido₄ monomer; additional alkylation converts either monomer or dimer to a P420.