Question

What are the enzymes in which zinc ion is bound tightly to the enzyme and is not dissociated even after several steps of purification?
A. Carbonic anhydrase
B. Alcoholdehydrogenase
C. Cytochrome oxidase
D. Glucose 6-phosphatase
E. Alkaline phosphatase
F. Lactate dehydrogenase
Choose the most appropriate answer from the option given below

• A. A, B, C, D, E
• B. B, C, D, E, F
• C. A, B, E, F
• D. C, D, E, F

Hint:

Zinc Metalloenzymes: Carbonic Anhydrase, Alcohol Dehydrogenase, Alkaline Phosphatase, Carboxypeptidase A, DNA/RNA Polymerases.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Zinc metalloenzymes contain catalytic and structural zinc ($ ext{Zn}^{2+}$) ions coordinated tightly via histidine and cysteine residues.

Step 2: Detailed Explanation:
Evaluating zinc-dependent metalloenzymes:
1. A. Carbonic Anhydrase: Classic zinc metalloenzyme; $\text{Zn}^{2+}$ is coordinated to three histidine imidazoles, polarizing water for rapid hydration of $\text{CO}_2$.
2. B. Alcohol Dehydrogenase: Contains structural and catalytic $\text{Zn}^{2+}$ ions.
3. E. Alkaline Phosphatase: Dimeric metalloenzyme containing two catalytic $\text{Zn}^{2+}$ ions and one $\text{Mg}^{2+}$ per active site.
4. F. Lactate Dehydrogenase (LDH): Contains essential divalent catalytic metal centers.
(Cytochrome oxidase contains Cu and Fe).
Thus, A, B, E, and F are tightly bound metalloenzymes.

Step 3: Final Answer:
Therefore, the zinc metalloenzymes are A, B, E, F, corresponding to option (C).