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

A rapid and simple procedure for the preparation of sperm whale ferrimyoglobin is described. The method involves homogenization in 70% saturated ammonium sulfate at 4° and chromatography on carboxymethyl Sephadex. The major component was judged to be homogeneous by electrophoresis at two pH values and by analytical chromatography on sulfoethyl Sephadex at a third pH value. The method has also been utilized to prepare electrophoretically pure myoglobin from harbor seal and porpoise. The amino acid composition and amino-terminal end groups of harbor seal and porpoise myoglobin have been determined, and the results compared with sperm whale myoglobin. Each protein was found to possess 153 amino acid residues with a single amino-terminal end group. Both harbor seal and porpoise myoglobins have glycine as the amino-terminal residue, in contrast to the sperm whale protein, which contains a single residue of valine. The amino acid compositions indicate a close similarity among all three myoglobins and suggest that only a limited number of amino acid substitutions in the primary structure differentiates the three proteins. The molar extinction coefficients and the reduced mean residue rotation at 233 mµ were found to be essentially identical in the three myoglobins, indicating that the three-dimensional structure in solution is probably very nearly identical for sperm whale, harbor seal, and porpoise ferrimyoglobins.