A 6-month-old boy admitted with failure to thrive with high glutamine and Uracil in urine. Hypoglycemia, high blood ammonia. Treatment given for 2 months. At 8 months again admitted for failure to gain weight. Gastric tube feeding was not tolerated. Child became comatose. Parenteral Dextrose given. Child recovered from coma within 24 hours. What is the enzyme defect?