Comparative Structural Studies of the Active Site of ATP‐Guanidine Phosphotransferases

The purification and the amino acid sequence of the peptide containing the essential sulphydryl group of arginine kinase from Homarus vulgaris muscle is described. The fractionation of the tryptic digest of arginine kinase labelled with N‐[1‐14C]ethylamaleimide has been carried out using gel filtration, ion‐exchange chromatography and paper chromatography. The composition of the radioactive peptide, isolated from the digest, is reported together with its amino acid sequence. A structural comparison is made between the peptide of arginine kinase and the corresponding active‐cysteine containing peptide isolated from rabbit muscle creatine kinase.