PRIMARY STRUCTURE OF LOBSTER-MUSCLE ARGININE KINASE: Amino and Carboxyl-terminal Structure of the Enzyme and Complete Alignment of the Cyanogen-Bromide Peptides

The acetylation state of the blocked NH₂-terminal end of arginine kinase was characterized by the occurrence of 1 mol acetyl group/mol protein; a 5-residue segment corresponding to the amino-terminal portion was isolated from a pronase digest of the enzyme and its amino acid sequence determined as N-acetyl Ala-Asx-Ala-Ala-Thr. Arginine kinase is terminated at the carboxyl end by the sequence Lys-Glu-MetOH; this particular 3-residue sequence is repeated three times in the overall structure of the protein and is present in three CNBr fragments. One of these, a peptide of 14 amino acid residues, was identified in the course of this study and its amino acid sequence determined. Its location at the COHO-terminal end of the enzyme was recognized on the basis of investigations carried out with des-MetOH-Glu-arginine kinase, a specific proteolytic derivative. The alignment of the eight CNBr-fragments which constitute the arginine kinase molecule was established according to the sequential and compositional properties of seven unique tryptic methionyl peptides isolated from the whole protein. The alignment was confirmed by using BNPS-skatole fragments of the enzyme as another protein source.