Question

The enzyme that catalyses the first step in nitrate assimilation is

• A. Nitrate reductase
• B. Nitrite reductase
• C. Glutamate synthase
• D. Aminotransferase

Hint:

Nitrate assimilation:
1. Nitrate reductase: NO3- → NO2-
2. Nitrite reductase: NO2- → NH4+
Nitrate reductase is the key regulatory enzyme.

Answer 1

The Correct Option is A

Step 1: Understanding the Question:
This question tests knowledge of nitrate assimilation.

Step 2: Detailed Explanation:
Nitrate reductase catalyses the first step in nitrate assimilation.
It reduces nitrate (NO3-) to nitrite (NO2-).
This is the rate-limiting step in nitrate assimilation.
Nitrite reductase (B): Reduces nitrite to ammonium.
Glutamate synthase (C): Incorporates ammonium into glutamate.
Aminotransferase (D): Transfers amino groups.
Thus, nitrate reductase catalyses the first step.

Step 3: Final Answer:
Thus, nitrate reductase catalyses the first step, which corresponds to option (A).
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