Cytochrome P-450cam

The b-type cytochrome P-450cam in the active ferric form, purified from camphor-grown Pseudomonas putida, has a Soret absorption band at 417 nm. Upon reduction to the ferrous form the Soret band shifts to 411 nm, and on addition of CO, to 446 nm. An enzymatically inactive cytochrome forms on treatment of P-450cam with mercurial compounds, acetone, sodium deoxycholate, or urea; all possess ferrous CO Soret absorption at 420 nm. All these biologically inactive forms are termed P-420. They are reconverted to the catalytically active P-450cam by treatment with sulfhydryl compounds such as cysteine, thioglycolic acid, β-mercaptoethanol, or dithioerythritol. Six sulfhydryl groups can be titrated with p-chloromercuribenzoate, corresponding to the total of 6 cysteine residues found by amino acid analysis.