Amino acid sequence of hemerythrin from Themiste dyscritum.

The amino acid sequence of hemerythrin from the sipunculid worm, Themiste dyscritum, was determined by sequenator analyses of the S-pyridylethylated protein and fragments derived by further chemical and enzymatic cleavages. The fragments were obtained by cleavage of the intact protein with hydroxylamine, trypsin digestion of citraconylated intact protein, and subdigestion with Staphylococcal protease V8. The COOH-terminal sequence was determined using carboxypeptidases A and B and amino acid analyses. The polypeptide chain was found to contain 113 amino acids. Since heterogeneity was observed at no more than two positions in the amino acid sequence, the native octameric protein appears to be composed of identical subunits. By combining information derived from sequence analyses and x-ray crystallographic studies, it has been possible to identify amino acids responsible for the tertiary and quaternary structure of the protein as well as amino acids serving as iron ligands at the oxygen-binding site.