PLE-1344

A 28-year-old male with a history of recurrent nephrolithiasis comes in due to severe intermittent right flank pain and hematuria. On examination, you note CVA tenderness on the right. Urinalysis reveals hexagonal crystals upon cooling of acidified urine sediment. The patient tells you that a physician who saw him for a previous bout of nephrolithiasis was considering an inherited condition. You suspect that the patient may have a condition characterized by impaired renal tubular absorption of which of the following amino acids?