Redox potential covalent linkages

Protein cross linkages are important in determining the chemical properties of these novel cofactors. In galactose oxidase, the covalent link between the cysteine and tyrosine helps lower the redox potential of the radical to a value consistent with its ready generation in vivo. In lysyl oxidase, however, the quinone derived from trihydroxyphenylalanine... 

The redox potentials, heme accessibility, and sites of covalent linkage have been examined in a covalently linked 1 1 PC-cyt f adduct. The redox potential of cyt f, but not of PC, was observed to be shifted relative to that observed with the free protein, suggesting a possible alteration of the heme environment. Although it is not known whether this shift is physiologically relevant, it is interesting that it is in the direction which would favor electron transfer from cyt f to PC. 

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