Q. A 2-year-old boy is brought to the clinic by his parents due to frequent episodes of vomiting and lethargy. His pediatrician also notes developmental delay. Lab tests reveal high levels of ammonia in his blood. Further biochemical analysis suggests a deficiency in the Carbamoyl Phosphate synthetase I enzyme within the urea cycle. The parents are informed that this enzyme is stimulated by a certain molecule. Which of the following molecules is the allosteric activator for this enzyme?