Electron paramagnetic resonance and resonance Raman spectroscopic investigations of the ferric ligand complexes and the oxidized intermediates of catalase and bromoperoxidase

Catalase (M. luteus) and bromoperoxidase (P. capitatus) are hemeproteins which are members of a broad family of enzymes known as hydroperoxidases. These enzymes are characterized by their ability to oxidize suitable substrates using hydrogen peroxide. The native enzymes and their fluoride, azide and cyanide ferric derivatives were investigated using electron paramagnetic resonance (EPR) and resonance Raman (RR) spectroscopies. Crystal field parameters derived from EPR data indicate a tyrosine fifth ligand for catalase. The general features of RR spectra for bacterial catalase and its various derivatives are typical of those obtained for other ferric hemeproteins. The oxidation state marker band, $\nu\sb4$, is at 1377 cm$\sp{-1}$ for the native enzyme. The observation of vinyl stretching modes at 1626 cm$\sp{-1}$ indicates unmodified vinyl porphyrin substituents. Crystal field parameters for bromoperoxidase suggest that a histidine fifth ligand is present in the active site. High-frequency RR spectra for the enzyme and its various derivatives show unique positions for the vinyl stretching modes. Energy increases of 5-7 cm$\sp{-1}$ are seen relative to other characterized hemeproteins. The low-frequency spectra obtained are similar to those observed for lactoperoxidase and hog intestinal peroxidase. A band at 264 cm$\sp{-1}$ is tentatively assigned to an iron-imidazole stretch arising from the proposed histidine fifth ligand. The oxidized intermediates present in the reaction cycles of the two enzymes were also investigated. EPR free radical signals associated with the putative $\pi$ cation radical structure of compound I are shown for both catalase and bromoperoxidase. In addition, RR spectra were obtained for compound I and compound II intermediates of the catalase reaction. Compound I is assigned a $\nu\sb4$ band at 1374 cm$\sp{-1}$, while the oxidation state marker for compound II is seen at 1378 cm$\sp{-1}$. Down shifts of the $\nu\sb2$ band of compound I relative to that of compound II is similar to an A$\sb{2\rm u}$ $\pi$ cation radical for metalloporphyrin model compounds.U of I OnlyETDs are only available to UIUC Users without author permissio