At the time of weaning, a 6 month old infant has irritability and vomiting. Studies show recurrent episodes of hypoglycemia after feeding, fructosuria, hepatomegaly, jaundice, aminoaciduria, a metabolic acidosis, and low urine ketones. The child begins to develop failure to thrive. Milk is okay. Sweets and fruits are not. This is not a glycogen- or gluconeogenesis-related problem.
Challenge: This is a recessive disorder caused by deficiency in what enzyme?