Studies on Cytochrome c Peroxidase

Light absorption spectra of cytochrome c peroxidase and its derivatives are measured between 23° and -190°. Spectra of the enzyme and its azide complex are found to be temperature-dependent, while those of Complex ES (a red peroxide compound) and of complexes of the enzyme with cyanide and fluoride appear temperature-independent. The spectrum of the enzyme at pH 7.0, which is a predominantly high spin type at 23°, changes to an essentially low spin type on cooling at -190°. This spectral transition of the frozen enzyme is found to take place in a relatively limited range of cryogenic temperature from -10° to -100°. Upon warming the frozen enzyme up from -190°, it is found that the α- and β-bands at 574 and 540 mµ (low spin type) disappear in a range from -100° to -30°, while the charge transfer bands at 500 and 640 mµ (high spin type) appear in a range from -60° to -10°.