Which process contributes to the excretion of nitrogen in the urine as ammonium?

The process that contributes to the excretion of nitrogen in the urine as ammonium is oxidative deamination. This biochemical reaction primarily occurs in the liver and is crucial for the metabolism of amino acids. During oxidative deamination, an amino group is removed from an amino acid, converting it into a corresponding keto acid and releasing ammonia (NH3) in the process.

The ammonia can then combine with protons (H+) to form ammonium (NH4+), which is a more stable form that gets excreted in the urine. This reaction not only helps remove excess nitrogen from the body but also plays a significant role in the urea cycle, where additional processing of nitrogen waste occurs.

Other processes mentioned, such as transamination, are important for amino acid metabolism but do not directly lead to nitrogen excretion as ammonium. Glycogenesis is related to the synthesis of glycogen from glucose, and cysteine synthesis pertains specifically to the production of the amino acid cysteine, neither of which are involved in nitrogen excretion. Thus, oxidative deamination is a critical step in the pathway that leads to nitrogen being excreted in the form of ammonium in urine.