The myoglobin protein radical. Coupling of Tyr-103 to Tyr-151 in the H2O2-mediated cross-linking of sperm whale myoglobin.
Sperm whale metmyoglobin, which has tyrosine residues at positions 103, 146, and 151, dimerizes in the presence of H2O2. Equine metmyoglobin, which lacks Tyr-151, and red kangaroo metmyoglobin, which lacks Tyr-103 and Tyr-151, do not dimerize in the presence of H2O2. The dityrosine content of the sperm whale myoglobin dimer shows that it is primarily held together by dityrosine cross-links, although more tyrosine residues are lost than are accounted for by dityrosine formation. Digestion of the myoglobin dimer with chymotrypsin yields a peptide with the fluorescence spectrum of dityrosine. The amino acid composition, amino acid sequence, and mass spectrum of the peptide show that cross-linking involves covalent bond formation between Tyr-103 of one myoglobin chain and Tyr-151 of the other. Replacement of the prosthetic group of sperm whale myoglobin with zinc protoporphyrin IX prevents H2O2-induced dimerization even when intact horse metmyoglobin is present in the incubation. This suggests that the tyrosine radicals required for the dimerization reaction are generated by intra- rather than intermolecular electron transfer to the ferryl heme. Rapid electron transfer from Tyr-103 to the ferryl heme followed by slower electron transfer from Tyr-151 to Tyr-103 is most consistent with the present results.
Tew
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Department of Pharmaceutical Chemistry, School of Pharmacy and Liver Center, University of California, San Francisco 94143-0446.
Ortiz de Montellano
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D000818:Animals; D002851:Chromatography, High Pressure Liquid; D003198:Computer Simulation; D003432:Cross-Linking Reagents; D006861:Hydrogen Peroxide / Q000494:pharmacology*; D046911:Macromolecular Substances; D013058:Mass Spectrometry; D008958:Models, Molecular; D009211:Myoglobin / Q000378:metabolism*; D011487:Protein Conformation; D014443:Tyrosine; D014907:Whales
D003432:Cross-Linking Reagents; D046911:Macromolecular Substances; D009211:Myoglobin; D014443:Tyrosine; D006861:Hydrogen Peroxide