Hydrolysis of a thiopeptide by cadmium carboxypeptidase A |
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Authors: | William L. Mock Jin-Tann Chen Joseph W. Tsang |
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Affiliation: | Department of Chemistry, University of Illinois at Chicago Circle, Box 4348, Chicago, Illinois 60680 USA |
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Abstract: | Substitution of the active site zinc ion of carboxypeptidase A by cadmium yields an enzyme inactive towards ordinary peptide substrates. However, a substrate analog (BzGlyNHCH2CSPheOH) containing a thioamide linkage at the scissile position is cleaved to the thioacid. The kinetic parameters and their pH dependencies are , decreasing with either acid or base (PKE1 = 5.64, pKE2 = 9.55), and kcat = 1.02 × 102 min?1, decreasing with acid (pKES = 6.61). The thiopeptide is less efficiently cleaved by native (zinc) carboxypeptidase A. This cadmium-sulfur synergism supports a mechanism wherein the substrate amide is activated by metal ion coordination to its (thio) carbonyl. |
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