Question

Match List I with List II
List I (Enzyme):
A. Glutamate dehydrogenase
B. GS
C. GOGAT
D. Glutamate decarboxylase

List II (Reaction catalyzed):
I. Catalyzes ATP-dependent conversion of glutamate to glutamine using ammonium as substrate.
II. Catalyzes reductive amination of 2-oxoglutarate to form glutamate using ammonium as substrate.
III. Catalyzes the synthesis of two molecules of glutamate from glutamine and $\alpha$-ketoglutarate.
IV. Catalyzes the synthesis of GABA from glutamate.
V. Catalyses synthesis of aminolevulinic acid in the chlorophyll biosynthetic pathway.

Choose the correct answer from the options given below:

• A. A - I, B - II, C - III, D - V
• B. A - II, B - I, C - III, D - IV
• C. A - I, B - III, C - II, D - V
• D. A - III, B - I, C - II, D - IV

Hint:

To remember the nitrogen assimilation enzymes:
GS $\rightarrow$ Converts glutamate to glutamine (requires ATP).
GOGAT $\rightarrow$ Combines glutamine and $\alpha$-ketoglutarate to yield two glutamates.
GDH $\rightarrow$ Directly aminates $\alpha$-ketoglutarate to form glutamate.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Nitrogen assimilation in plants involves the conversion of inorganic ammonium ($\text{NH}_4^+$) into organic nitrogen compounds.
This process is regulated by enzymes that catalyze the synthesis and interconversion of amino acids like glutamate, glutamine, and their derivatives.

Step 2: Detailed Explanation:
Let us match the enzymes in List I with their corresponding reactions in List II:
1. Glutamate dehydrogenase (GDH) (A): Catalyzes the reversible, nicotinamide coenzyme-dependent reductive amination of 2-oxoglutarate (also known as $\alpha$-ketoglutarate) to form glutamate using free ammonium as a substrate:
\[ \text{2-oxoglutarate} + \text{NH}_4^+ + \text{NAD(P)H} + \text{H}^+ \rightleftharpoons \text{Glutamate} + \text{NAD(P)}^+ + \text{H}_2\text{O} \]
Thus, A matches with II.
2. Glutamine Synthetase (GS) (B): Catalyzes the ATP-dependent incorporation of ammonium into glutamate to produce glutamine. This is the primary pathway for ammonium assimilation in plants:
\[ \text{Glutamate} + \text{NH}_4^+ + \text{ATP} \rightarrow \text{Glutamine} + \text{ADP} + \text{P}_i \]
Thus, B matches with I.
3. Glutamate Synthase GOGAT (C): Catalyzes the transfer of the amide group from glutamine to 2-oxoglutarate, producing two molecules of glutamate:
\[ \text{Glutamine} + \text{2-oxoglutarate} + \text{Fd}_{\text{red}} \rightarrow 2\text{ Glutamate} + \text{Fd}_{\text{ox}} \]
Thus, C matches with III.
4. Glutamate Decarboxylase (D): Catalyzes the decarboxylation of glutamate, releasing carbon dioxide to produce GABA ($\gamma$-aminobutyric acid), a non-protein amino acid involved in stress responses:
\[ \text{Glutamate} \rightarrow \text{GABA} + \text{CO}_2 \]
Thus, D matches with IV.
This matches the sequence: A - II, B - I, C - III, D - IV.

Step 3: Final Answer:
The correct matching sequence is A - II, B - I, C - III, D - IV, which corresponds to Option (B).