High spins superoxide dismutase

FIGURE 5.11 EPR of an S = 5/2 system with pronounced rhombicity. The X-band spectra (V = 9.31 GHz) are from high-spin FeIH in Escherichia coli iron superoxide dismutase. The observed effective g-values correspond to T = 0.24 in the S = 5/2 rhombogram. 

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with NO that resembles the lipoxygenase-NO adduct by EPR criteria (I. Fridovich, T. Kirby, and J. C. Salerno, (1978) unpublished observations). 

Cobalt has recently been used as an ESR active substitute in zinc metalloenzymes. Whilst liquid helium temperatures may be needed and theoretical aspects of the spectra are not yet as well understood, cobalt has two important advantages over copper as a metal substitute, namely that many cobalt derivatives show some enzymic activity (e.g. cobalt in carbonic anhydrase, alkaline phosphatase and superoxide dismutase) and that g values and hyperfine splitting are more sensitive to ligand environment, particularly when low spin. ESR data have been reported for cobalt substituted thermolysin, carboxypeptidase A, procarboxypeptidase A and alkaline phosphatase [51]. These are all high spin complexes. Cobalt carbonic anhydrase has been prepared and reacted with cyanide [52]. In... 

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