This byproduct of protein catabolism constitutes approximately one half of all nitrogenous waste Urea Creatinine Uric acid Ammonia

The correct answer to the question is Urea.

Explanation:

Urea is a nitrogenous waste product formed in the liver through the urea cycle, which plays a significant role in the excretion of excess nitrogen from the body resulting from the breakdown of proteins. It constitutes a major component of urine and represents approximately half of all nitrogenous waste produced by the body.

In contrast, creatinine is a byproduct of muscle metabolism, uric acid is produced from the breakdown of purines, and ammonia is highly toxic and is converted into urea for safer excretion. Thus, urea is the most significant nitrogenous waste product produced during protein catabolism.