Diamino acid transport into granulocytes and liver slices of patients with lysinuric protein intolerance.

Abstract

Uptake of diamino acids by isolated granulocytes and by liver slices was studied in patients with LPI and in control subjects. 14-C-Labeled lysine, arginine, and ornithine were used in the granulocyte assay and a nonmetabolizable diamino acid analog, l-homoarginine, in the liver assay. Kinetic studies on diamino acid uptake by the granulocytes were consistent with the existence of one transport system common to the three diamino acids. The maximal velocity of uptake was approximately equal for the three amino acids and similar in patients and control subjects. In the liver slices, at least two transport systems became apparent as substrate concentration was varied from 4.0-0.025 mM. A low concentration system with high affinity and very small capacity for transport was similar in patients and control subjects. A high concentration system was also present in both groups, but in the patients had only 1/7 of the maximal capacity observed in the control subjects. This defect grossly incapacitated the diamino acid uptake of the liver. In LPI, the observed defect, in conjunction with the deficient absorption in the kidneys and intestine, explains the lack of ornithine at the site of urea synthesis, which is evident from the impaired and ornithine-correctable urea production.