Cystinuria: Defective Intestinal Transport of Dibasic Amino Acids and Cystine*

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Abstract
Investigations of amino acid transport by jejunal mucosa in vitro indicate that amino acids are accumulated against concentration gradients by saturable systems that are energy dependent. A defect in the transport of cystine and the dibasic amino acids is described in jejunal tissue from patients with cystinuria. The intestinal transport defect in cystinuria differs significantly from the previously reported renal defect. Cystine transport was defective in the intestine but not in the kidney, whereas dibasic amino acid transport was defective in both tissues. Furthermore, cystine and lysine were mutually inhibitory in the gut but not in the kidney. Two patients with typical cystinuria had normal intestinal transport of cystine but reduced transport of arginine and lysine. A possible explanation of this phenomena on genetic grounds is presented.