Myoglobins of cartilaginous fishes III. Amino acid sequence of myoglobin of the shark Galeorhinus australis.

Myoglobin isolated from the red muscle of the school shark Galeorhinus australis was purified by gel filtration and ion-exchange chromatography. The amino acid sequence was determined following digestion with trypsin and purification of the peptides by paper ionophoresis and chromatography. Sequences of purified peptides were determined by the dansyl-Edman procedure and the peptides aligned by homology with the sequence of the myoglobin of the gummy shark Mustelus antarcticus. The two myoglobin sequences showed a marked similarity (16 differences), but both sequences showed approximately the same number of differences (68) from myoglobin of the Port Jackson shark Heterodontus portusjacksoni. There are 19 residues unique to three shark myoglobin sequences. As found with other fish myoglobins there are 148 residues with deletions of four residues at the amino terminal end as well as one residue in the CD region. The amino terminal residue is acetylated. The distal E7 histidine residue was found to be replaced by glutamine, as only previously reported for the myoglobin sequence of gummy shark.