Question

The production of ammonia in the reaction catalyzed by glutamate dehydrogenase A. requires the participation of NADH or NADPH. B. proceeds through a Schiff base intermediate. C. may be reversed to consume ammonia if it is present in excess. D. is favored by high levels of ATP or GTP. E. would be inhibited when gluconeogenesis is active.

Short answer

A. The production of ammonia in the reaction catalyzed by glutamate dehydrogenase requires the participation of NADH or NADPH. B. The reaction catalyzed by glutamate dehydrogenase proceeds through a Schiff base intermediate. C. The production of ammonia in the reaction catalyzed by glutamate dehydrogenase may be reversed to consume ammonia if it is present in excess. D. The production of ammonia in the reaction catalyzed by glutamate dehydrogenase is favored by high levels of ATP or GTP. E. The production of ammonia in the reaction catalyzed by glutamate dehydrogenase would be inhibited when gluconeogenesis is active. Answer: A, C, and E are true.

Step-by-step solution

Option A

The production of ammonia in the reaction catalyzed by glutamate dehydrogenase requires the participation of NADH or NADPH. Glutamate dehydrogenase catalyzes the reversible oxidative deamination of glutamate, leading to the formation of ammonia and α-ketoglutarate. This reaction involves the transfer of electrons from the substrate to NAD(P)+ molecules, which are reduced to NAD(P)H. Therefore, Option A is correct.

Option B

The reaction catalyzed by glutamate dehydrogenase proceeds through a Schiff base intermediate. In this reaction, the glutamate dehydrogenase active site includes a conserved catalytic cysteine residue. This residue forms a covalent thioester intermediate with the substrate, followed by nucleophilic attack by a water molecule, leading to the release of ammonia and α-ketoglutarate. This reaction does not involve the formation of a Schiff base intermediate. Hence, Option B is incorrect.

Option C

The production of ammonia in the reaction catalyzed by glutamate dehydrogenase may be reversed to consume ammonia if it is present in excess. As mentioned before, the reaction catalyzed by glutamate dehydrogenase is reversible. Under certain conditions, the enzyme can catalyze the reductive amination of α-ketoglutarate to form glutamate by consuming ammonium ions. This is particularly relevant when ammonia levels are high. Therefore, Option C is correct.

Option D

The production of ammonia in the reaction catalyzed by glutamate dehydrogenase is favored by high levels of ATP or GTP. Usually, high levels of ATP or GTP suggest that there is enough energy available for the cell, so there is no need for the oxidative deamination of glutamate in order to generate more energy. Therefore, high levels of ATP or GTP would inhibit the production of ammonia in the reaction catalyzed by glutamate dehydrogenase. As a result, Option D is incorrect.

Option E

The production of ammonia in the reaction catalyzed by glutamate dehydrogenase would be inhibited when gluconeogenesis is active. During gluconeogenesis, the cell is synthesizing glucose from non-carbohydrate sources like α-ketoglutarate. In this situation, the cell needs to preserve the α-ketoglutarate, so the production of ammonia through the reaction catalyzed by glutamate dehydrogenase would not be favored. Hence, Option E is correct. To summarize, the correct statements are: A. The production of ammonia in the reaction catalyzed by glutamate dehydrogenase requires the participation of NADH or NADPH. C. The production of ammonia in the reaction catalyzed by glutamate dehydrogenase may be reversed to consume ammonia if it is present in excess. E. The production of ammonia in the reaction catalyzed by glutamate dehydrogenase would be inhibited when gluconeogenesis is active.