Spectral similarities between "H-450" and cytochrome P-450.

The absorption spectrum of reduced H-450 was reversibly affected by a pH change; the Soret peak of the alkaline form was at 448 nm, and that of the acidic form (H-420) at 425 nm. The same spectral change of conversion of reduced H-450 to H-420 was also produced by the action of n-butanol, urea and p-chloromercuribenzoate. These spectral properties of H-450 were similar to those of the conversion of cytochrome P-450 to cytochrome P-420, suggesting the similar heme environments of these two hemoproteins. Reduced H-450 bound carbon monoxide to be transformed into a new spectral species having a Soret peak at 420 nm.