Carboxymethylation of Sperm Whale Metmyoglobin. Reactivity of the Adjacent Histidine Residues.

The reactivities of the imidazole groups of histidyl residues in sperm whale myoglobin are being studied systematically to achieve a correlation with three-dimensional structure (1, 2). In the sequence between the Eand F-helices there occur 2 histidyl residues, EF4 and EF5, that can be isolated in the same tryptic peptide (3, 4).l It has been shown previously that treatment with bromoacetate before tryptic digestion yields a corresponding peptide differing only in that, on the average, 1 histidyl residue is changed to the dicarboxymethyl derivative (1). The present report establishes that the residue EF4 is reactive towards bromoacetate and EF5 is not.