Nitric Oxide Complexes of Other Nonheme Iron Proteins

NITRIC OXIDE COMPLEXES OF OTHER NONHEME IRON PROTEINS 

The protocatechuate 3,4- and 4,5-dioxygenases also react with NO to form S = I complexes (Lipscomb et al., 1979). The EPR spectrum of the 3,4-dioxygenase—nitrosyl adduct has g values of 4.3, 3.7, and 2.0, whereas the EPR spectrum of the nitrosyl adduct of the 4,5-dioxygenase is similar to that of the lipoxygenase NO adduct. The differences in the EPR spectra are the result of the 

E/D ratios. The differences in coordination geometry implied by the EPR spectra need not be great. 

Other enzymes that are not obviously related to the dioxygenases have at least superficially similar metal sites. The fatty acid desaturase of the endoplasmic reticuluum is a nonheme iron protein and requires both oxygen and reducing equivalents for activity (Strittmatter and Enoch, 1978). It is not known whether this enzyme forms a nitroxyl complex, but rat liver microsomes containing the enzyme form an S = nitroxyl adduct when treated with nitrite and dithionite. 

Iron-containing superoxide dismutases are present in many species of bacteria (Hassan and Fridovitch, 1978). These nonheme iron proteins have a characteristic set of EPR lines split about g = 4.2 in the ferric state, arising from the middle Kramers doublet of a rhombic high-spin site. Ferrous iron superoxide dismutase forms an S = I complex with NO that resembles the lipoxygenase-NO adduct by EPR criteria (I. Fridovich, T. Kirby, and J. C. Salerno, (1978) unpublished observations). 

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VI. NITRIC OXIDE COMPLEXES OF OTHER NONHEME IRON PROTEINS... 

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