Comparison of Myoglobins from Harbor Seal, Porpoise, and Sperm Whale

Harbor seal myoglobin has been dehemed and treated with bromoacetate in 8 M urea for 9 days at pH 6.7 to produce a derivative that was exhaustively alkylated at the histidyl residues.In addition, both the methionyl residues and the amino-terminal glycyl residue were modified.The alkylated derivative was subjected to tryptic digestion and the hydrolysate was fractionated on columns of Dowex 50 and Dowex 1 with gradients of pyridine acetate.All of the peptides recovered could be aligned by analogy to the known sequence of the closely related sperm whale myoglobin to give a tentative sequence.By this technique, 85 of the 153 residues could be positioned from sequential Edman degradations or carboxypeptidase hydrolyses.Of the established group, 15 residues were different from those in the corresponding sperm whale protein and, from compositional data, a minimum of 10 additional replacements must also exist.Thus, excluding amide differences, the seal protein differs from the sperm whale protein in at least 25 positions.The tentative partial sequence obtained was in exact agreement with the previously established amino acid composition of the protein.Recent reports (24) have described the preparation, characterization, and reactivity of myoglobins isolated from harbor