Question

The enzyme requiring nickel in higher plants is

• A. Catalase
• B. Alkaline phosphatase
• C. Carbonic anhydrase
• D. Urease

Hint:

Nickel ($Ni$) is the most recently added essential plant micronutrient.
Its sole confirmed role in higher plants is serving as the active-site cofactor for the urease enzyme, which is essential for nitrogen recycling from urea.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Plants require essential micronutrients to serve as structural components or catalytic cofactors for specific metabolic enzymes.
Identifying these metal-enzyme relationships is important for understanding plant nutritional biochemistry.

Step 2: Detailed Explanation:
Let us analyze the cofactor requirements for each enzyme listed in the options:
Catalase is an oxidative enzyme that breaks down hydrogen peroxide into water and oxygen.
It contains a heme group, requiring iron ($Fe$) as its essential cofactor, matching Option (A).
Alkaline phosphatase is a hydrolase enzyme responsible for removing phosphate groups, requiring zinc ($Zn$) and magnesium ($Mg$) ions for its activity, matching Option (B).
Carbonic anhydrase catalyzes the reversible hydration of carbon dioxide to bicarbonate, requiring zinc ($Zn$) as its essential cofactor at the active site, matching Option (C).
Urease is the enzyme responsible for hydrolyzing urea into carbon dioxide and ammonia:
\[ (NH_2)_2CO + H_2O \rightarrow CO_2 + 2NH_3 \]
Urease is a metalloenzyme that contains two nickel ($Ni$) ions at its catalytic active site.
Because of this requirement, nickel was officially recognized as an essential micronutrient for higher plants in 1987, as plants grown in nickel-deficient conditions accumulate toxic levels of urea in their leaf tips, leading to necrosis.

Step 3: Final Answer:
Urease is the enzyme that requires nickel in higher plants.
This corresponds to Option (D).