PubMed · 9590015
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F Endo. 1998. [Hydroxyprolinemia].. https://pubmed.ncbi.nlm.nih.gov/9590015/
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We introduced a two-step procedure for the detection of defects in metabolism of tryptophan: (1) HPTLC (described previously) is suitable when starting the investigation, (2) two HPLC methods with isocratic elution and spectrophotometric detection are used at the next step, when pathological findings are to be confirmed and the individual metabolites quantified. The first method enables the assessment of tryptophan, 5-hydroxyindolylacetic acid, indolylacetic acid, indolylacryloylglycine, indolylacrylic acid and its possible precursors, namely indolyllactic and indolylpropionic acids. The second procedure is intended for the monitoring of anthranilic, 3-hydroxyanthranilic, kynurenic and xanthurenic acids, kynurenine, 3-hydroxykynurenine and indoxyl-sulfate. The same pre-treated sample is used for all methods.
Lysinuric protein intolerance (LPI; MIM 222700) is an autosomal recessive disorder characterized by defective transport of the cationic amino acids lysine, arginine and ornithine at the basolateral membrane of the polar epithelial cells in the intestine and renal tubules, and by hyperammonemia after high-protein meals. LPI is caused by mutations in the SLC7A7 (solute carrier family 7, member 7) gene encoding y(+)LAT-1 (y(+)L amino acid transporter-1), which co-induces together with 4F2 heavy chain (4F2hc) system y(+)L in Xenopus oocytes. All Finnish LPI patients share the same founder mutation 1181-2A-->T (LPI(Fin)) not found in LPI patients elsewhere. Mutation screening of 20 non-Finnish LPI patients revealed 10 novel mutations: four deletions, two missense mutations, two nonsense mutations, a splice site mutation and a tandem duplication. Five LPI mutations (L334R, G54V, 1291delCTTT, 1548delC and LPI(Fin)) were studied functionally. All mutant proteins failed to co-induce amino acid transport activity when expressed with 4F2hc in Xenopus oocytes. Immunostaining experiments revealed that frameshift mutants 1291delCTTT, 1548delC and LPI(Fin)remained intracellular on expression with 4F2hc. In contrast, the missense mutants L334R and G54V reached the oocyte plasma membrane when co-expressed with 4F2hc, demonstrating that they are transport-inactivating mutations. This finding, together with the strong degree of conservation among all members of this family of amino acid transporters, indicates that residues L334 and G54 play a crucial role in the function of the y(+)LAT-1 transporter.
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