Amino acid sequence of calmodulin from scallop (Patinopecten) adductor muscle.

The complete amino acid sequence of scallop calmodulin was determined by isolating and sequencing the peptides obtained after cyanogen bromide cleavage and tryptic digestion. The protein consisted of 148 amino acid residues and its amino(N)-terminus was blocked with an acetyl group. Scallop calmodulin lacked tryptophan and cysteine residues and contained one mol each of N epsilon-trimethyllysine (Tml) and histidine residues per mol of the protein. Scallop calmodulin contained only one tyrosine residue, while vertebrate calmodulins contain two. On comparing its amino acid sequence with that of bovine calmodulin, three amino acid substitutions were found at positions 99(Tyr leads to Phe), 143(Gln leads to Thr), and 147(Ala leads to Ser).