Our purpose is to study the properties of intramolecular long range electron transfer (LRET) between two redox centers attached to a single protein (methemerythrin) or polypeptide (L-polyglutamic acid) molecule but not in direct contact with one another. One of the two centers in methemerythrin will be its intrinsic oxidized 2-iron center. We shall introduce the other center by chemical modification of the lone cysteine on the protein, either to form a mixed aromatic to rapidly reduce, with either the pulse radiolytically generated hydrated electron (eag) or formate radical (C02), one or both of the redox sites on the target protein, and to then observe the subsequent lst order electron equilibration. The influence of the redox potential differnece between the two centers will be investigated iwth different lanthanide ions in the protein bound chelate and by variation of the substituents on the aromatic portion of the mixed disulfide. The two sites attached to the polyglutamate will be tryptophan and tyrosine as the terminal amino acid residues. The tryptophan side chain will be oxidized by the pulse radiolytically generated azide radical, and the subsequent transfer of an electron from the tyrosine phenol to the tryptophan indole monitored. The experiments will be done at a pH where the polyglutamyl portion of the polypeptide is expected to assume an alpha helical structure. The distance between the two redox centers will be varied by varying the number of intervening glutamyl residues. The redox potential between the two centers will be varied by substitution into the phenol ring of the tyrosine. The purpose of these experiments is to gather information pertinant to the mechanism of LRET in proteins.
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