Comparison of Myoglobins from Harbor Seal, Porpoise and Sperm Whale

Myoglobins from sperm whale, harbor seal, and harbor porpoise were compared with respect to their behavior in several reactions. Qualitative similarities were established in each case, but quantitative differences were also observed. Despite close similarities in the hydrogen ion titration curves, the titration parameters of the imidazole groups were not identical. In this respect, the whale and porpoise proteins showed the most points of similarity. By contrast, the hemic acid dissociation constants for the seal and porpoise proteins were indistinguishable, and differed from the value for the whale protein by approximately 0.33 in pK units. The sharpest contrasts were obtained in the rates of denaturation by cupric ion, in which the whale protein was set apart in two respects. First, its reaction rate was much slower in an inert buffer. Second, its reaction rate was much more effectively depressed by addition of small quantities of phosphate.