How is the enzymatic reaction for BUN measurement linked to ammonia levels?

The measurement of Blood Urea Nitrogen (BUN) is closely linked to ammonia levels through a specific enzymatic reaction that involves the coupling of urease and glutamate dehydrogenase. In this method, urease catalyzes the hydrolysis of urea to form ammonia and carbon dioxide. The ammonia produced can then be quantified as it is a byproduct of the enzymatic reaction.

Glutamate dehydrogenase plays an important role in further processing the ammonia, as it catalyzes the oxidative deamination of glutamate to regenerate α-ketoglutarate while simultaneously incorporating ammonia in the process, thus linking the two measurements. This coupling allows for efficient quantification of ammonia levels indirectly via the measurement of BUN, as it reflects changes in nitrogen metabolism and can indicate liver and kidney function.

The other options do not effectively capture the relationship between BUN measurement and ammonia levels. Measuring glucose as a byproduct does not provide information about ammonia. Direct sampling of ammonia does not utilize the enzymatic reaction involving urease and glutamate dehydrogenase. Finally, while a metabolic pathway may play a role, the specific coupling of these two enzymes directly illustrates how BUN measurement is related to ammonia levels.