Studies on the Zn2+/Co2+ exchange with acylamino acid amidohydrolase from pig kidney

The kinetics of inactivation of the Zn2+-metalloenzyme acyl-amino acid amido hydrolase by chelating ligands were studied. The rate of inactivation by 1,10-phenanthroline is enhanced by histidine and inhibited in the presence of phenyl-alanine. Removal of the metal ion increases the heat stability and decreases the pH stability of the enzyme. Reactivation of the inactive metal free enzyme is possible with Zn2+ and Co2+. Titration of the metal free protein with a free enzyme is possible with Zn2+ and Co2+. Titration of the metal free protein with a Co2+/nitrilotriacetate metal buffer revealed a dissociation constant of about 10(-7) M for the Co2+ enzyme (Zn2+ enzyme = 10(-10) M). The Co2+ substituted enzyme is less stable than the Zn2+ enzyme. Histidine and phenylalanine protect the Co2+ enzyme against inactivation by 1,10-phenanthroline.