Abstract
β-Naphthylamides of p-guanidino-L-phenylalanine (GPA) and p-guanidino-DL-phenylglycine (GPG) were synthesized and tested as substrates of bovine leukocyte aminopeptidase (BL-APase) and porcine liver aminopeptidase B (PL-APaseB) in comparison with L-arginine β-naphthylamide (Arg-βNA). BL-APase-catalyzed bydrolysis of GPA-βNA proceeded as fast as that of Arg-βNA, while the rate of hydrolysis of GPG-βNA was much slower. The specificity constant (Vmax/Km) for the hydrolysis of GPA-βNA by BL-APase was somewhat larger than that for the hydrolysis of Arg-βNA. The benzene ring in the side chain of GPA-βNA is considered to contribute to the binding of this substrate to the specificity side to this enzyme, based on comparison of the Km values for the two β-naphthylamide substrates. Substrate inhibition was observed with BL-APase in the hydrolysis of GPA-βNA in the substrate concentration range higher than about 0.1 mM. Neither GPA-βNA nor GPG-βNA was hydrolyzed by PL-APaseB and they inhibited the hydrolysis of Arg-βNA by this enzyme. GPA-βNA is expected to be a useful substrate in the study of the binding and catalytic specificities of aminopeptidases.
