• Metalloenzyme Co-factors:
• Urease:
• The historical enzyme first crystallized in 1926 by James B. Sumner (Jack bean Canavalia ensiformis urease), proving that enzymes are pure proteins.
• It is a classic Nickel-containing metalloenzyme whose catalytic active site coordinates two essential nickel ($Ni^{2+}$) ions per active subunit to catalyze the hydrolytic cleavage of urea into ammonia and $CO_2$.
• Carbonic anhydrase contains Zinc ($Zn^{2+}$).
• nalysis:
• (Urease): Correct nickel-containing enzyme.

Correct option: (1) Urease

• Enzyme Classes in the EC Classification System:
• The International Union of Biochemistry and Molecular Biology (IUBMB) classifies all enzymes into six primary hierarchical classes (EC 1 to EC 6):

• EC 1: Oxidoreductases
• EC 2: Transferases (B)
• EC 3: Hydrolases (A)
• EC 4: Lyases
• EC 5: Isomerases (C)
  6. EC 6: Ligases (D)
  (EC 7 Translocases was added subsequently).
  • nalysis:

• All four listed groups (A, B, C, D) are official major enzyme classes. Hence, Option 3 is correct.