Review Question - QID 212880

A 6-month-old infant male is brought to the emergency department with a 1-hour history of vomiting and convulsions. He was born at home and had sporadic prenatal care though his parents say that he appeared healthy at birth. He initially fed well; however, his parents have noticed that he has been feeding poorly and is very irritable since they moved on to baby foods. They have also noticed mild yellowing of his skin but assumed it would go away over time. On presentation, he is found to be very sleepy, and physical exam reveals an enlarged liver and spleen. The rest of the physical exam is normal. Which of the following enzymes is most likely functioning abnormally in this patient?