| Abstract: | The hydrolysis of a series of depsipeptides demonstrates that the zinc neutral endopeptidases of bacteria are active esterases. Esters such as BzGly-OPhe-Ala, BzGly-OLeu-Ala, and FA-Gly-OLeu-NH2 are hydrolyzed at rates three- to eightfold slower than are their exact peptide analogues, when hydrolyzed by thermolysin, Bacillus subtilis neutral protease and the neutral protease from Aeromonas proteolytica. Ester hydrolysis by zinc neutral proteases follows the characteristic preference for hydrophobic amino acids adjacent to the site of cleavage, discerned from the hydrolysis of peptide substrates. Removal of zinc from thermolysin abolishes the esterase activity of the native enzyme. Among the metals examined, only Co2+ and Zn2+ restore esterase activity to any significant extent, Co2+ restoring 50% and Zn2+ 100% of the native thermolysin activity. The hydrolysis of esters and peptides by thermolysin does not differ with respect to either the binding or catalytic steps. Substrate specificity, pH-rate profiles, inhibitor, and deuterium isotope effects are identical for both types of substrates. |
