What are the substrates required for the enzymatic measurement of ammonia?

The correct answer identifies α-ketoglutarate and NADH as the substrates necessary for the enzymatic measurement of ammonia. This measurement typically involves the enzyme glutamate dehydrogenase, which catalyzes the reaction between ammonia and α-ketoglutarate to form glutamate. During this reaction, NADH is oxidized to NAD+, and this change can be monitored spectrophotometrically.

The utilization of α-ketoglutarate is critical, as it acts as an acceptor for the ammonia, integrating it into a metabolic pathway central to amino acid metabolism. The involvement of NADH in this reaction allows for the quantification of ammonia levels based on the decrease in absorbance at a specific wavelength, reflecting the conversion of NADH to NAD+.

In contrast, the other options represent substrates or coenzymes not typically involved in the specific enzymatic determination of ammonia. Citric acid, while a component of the citric acid cycle, does not specifically relate to ammonia measurement. Glutamate and FADH2 could relate to other metabolic pathways but do not directly apply to the ammonia determination process. Similarly, urea and coenzyme A are not relevant substrates in this context. Thus, the choice of α-ket