Final answer:
Ammonium formation from ammonia in the kidneys occurs at an acidic pH, due to acidemia. This process helps regulate the acid-base balance and is a response to the higher concentration of H+ ions.
Step-by-step explanation:
The formation of ammonium (NH4+) from ammonia (NH3) in the tubular lumen of the kidney is initiated at an acidic pH. This process is related to acidemia, which is a condition where the arterial pH is lower than normal. Under these acidic conditions, the higher concentration of hydrogen ions (H+) combines with ammonia (NH3), which is a byproduct of protein metabolism. NH3 is converted into NH4+ primarily by the enzyme glutaminase in the kidney tubules, as part of nitrogen waste regulation and acid-base balance.
In the kidneys, this reaction helps conserve cations like Na+ and K+ ions and supports the excretion of acid. Overall, acidemia, marked by an acidic pH, enhances the conversion process from ammonia to ammonium, facilitating the body's ability to maintain a stable pH and electrolyte balance.