Effects of N-terminal deletion mutation on arginine kinase from the sea cucumber Stichopus japonicus.

Deletion mutants of arginine kinase (AK) were constructed: AKND4, AKND6, AKND8, AKND10 (the first 4, 6, 8 and 10 amino acids of the N-terminal were deleted), to investigate the structural and functional roles of the N-terminal. Results showed that the deletion mutants assume less compact conformations compared to the wild-type, whereas no significant changes of the secondary or the quaternary structures were observed, implying that the deletions cause a perturbation in the tertiary structure or the hydrodynamic properties of the enzyme. The enzymatic and denaturing measurements showed that removal of the N-terminal residues decreased the activity and stability of the enzyme markedly. The instability increased in accord with the increased number of amino acid residues removed from the N-terminal of AK. It can be concluded that the N-terminal of AK plays an important role in maintaining the conformational stability and catalytic function of the enzyme.