They combine with either glycine or glutamine and are excreted in the urine. Subsequent synthesis of glycine and glutamine removes ammonia from the blood stream. ALD is treated with arginine supplements. This promotes synthesis of argininosuccinate, which can be excreted into urine. PKU accounts for about half of all patients with elevated plasma phenylalanine.
Alkaptonuria is caused by a deficiency in homogentisate dioxygenase.
Phenylacetate imparts a characteristic odor to the urine. It requires BH 4 which carries electrons from NADH to O 2 and becomes oxidized in the process. There are no abnormal metabolites produced in PKU, only normal metabolites present in abnormal qua ntities. The neurotoxicity is apparently due to excess phenylalanine, and NOT lack of tyrosine. However, the mechanism of neurotoxicity is unknown.