A 3-day-old male neonate born to non-consanguineous parents presents with poor feeding, lethargy, and vomiting. On examination, he is hypotonic and has a weak cry. Laboratory investigations reveal ammonia level of 380 µmol/L (normal <50), normal blood glucose, normal liver function tests, and normal organic acids on urine chromatography. Plasma amino acid analysis shows elevated glutamine and alanine. A diagnosis of urea cycle disorder is suspected. Which enzyme deficiency is most likely responsible, given the clinical presentation and biochemical pattern?