Difficulty: Easy
Correct Answer: Carboxypeptidase A
Explanation:
Introduction:Many enzymes require metal ions for catalytic activity or structural stability. Recognizing which enzymes are Zn-dependent helps in understanding catalytic mechanisms and inhibitor design.
Given Data / Assumptions:
Concept / Approach:
Zinc commonly functions as a Lewis acid to polarize water or substrate functional groups. Proteases such as carboxypeptidase A and matrix metalloproteinases are well-known Zn enzymes. Zn coordinates with histidine, glutamate, or aspartate side chains in the active site, activating water for nucleophilic attack on peptide bonds.
Step-by-Step Solution:
1) Identify known Zn proteases: carboxypeptidase A is archetypal.2) Evaluate alternatives: phosphorylase b kinase is regulated by Ca^2+ and phosphorylation, not Zn at its catalytic core.3) Tyrosine hydroxylase uses a non-heme Fe^2+ cofactor.4) Many PDEs are Mg^2+/Mn^2+ dependent rather than Zn-centered at catalysis.5) Pyruvate dehydrogenase complex uses thiamine pyrophosphate, lipoamide, FAD, NAD^+, and Mg^2+; Zn is not central.Verification / Alternative check:
Structural studies of carboxypeptidase A show tetrahedral Zn coordination essential for peptide bond hydrolysis.
Why Other Options Are Wrong:
B, D: These rely primarily on other metal ions (Ca^2+, Mg^2+/Mn^2+). C: Requires Fe^2+. E: PDH uses Mg^2+ with TPP; no Zn at the catalytic core.
Common Pitfalls:
Assuming all hydrolases are Zn-dependent; many are serine-, cysteine-, or metallo-enzymes with diverse cofactors.
Final Answer:
Carboxypeptidase A
Discussion & Comments