Iron-tyrosine charge-transfer band

Intermediates in the reaction of the dioxygenase ES complexes with O2 can be observed using stopped-flow kinetic methods. Two transient species are observed and both exhibit tyrosinate-to-iron(III) charge transfer bands, though the band shifts in energy... 

The optical spectrum of iron superoxide dismutase is characterized by a broad band near 350 nm that is attributoi to a li nd-to-metal charge transfer band. The relatively high energy for this transition indicates that tyrosine is not a ligand to the Fe(lII). The EPR-spectrum is characteristically rhombic Azide and fluoride are inhibitors of the enzymatic activity. Intriguinly, cyanide does not affect the catalytic action. As in the case with the Cu ZHj enzymes, hydro n peroxide readily destroys the reactivity of iron SOD s, whereas manganese superoxide dismutases remain unaffected... 

The Mn111 acid phosphatases have an intense band in the visible spectrum at 515-570 nm, assigned to tyrosine-Mn111 charge transfer. Unlike the iron proteins, they do not require mild reduction for maximum activity. The linear relation between the intensity of absorption at 515 nm and phosphatase activity indicates that the metal is essential for catalysis. Neither manganese protein shows a room temperature ESR spectrum, but on add denaturation they show a spectrum characteristic of high-spin Mn". Little is known at present about the mechanism of these reactions. 

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