title: Biochemical analysis of decreased ornithine transport activity in the liver mitochondria from patients with hyperornithinemia, hyperammonemia and homocitrullinuria.
abstract: Hyperornithinemia, hyperammonemia and homocitrullinuria (HHH disorder) is an inherited metabolic disorder which shows peculiar amino acid changes in the serum and urine. The primary defect is considered to be the transport of ornithine across the mitochondrial membrane, but there is no direct evidence for this so far. We have analyzed ornithine transport activities in the liver mitochondria from three patients with HHH disorder. In coupled liver mitochondria we demonstrated low activities of citrulline synthesis and low rates of ornithine uptake. However, there were no abnormalities in carbamoyl-phosphate synthetase activity, ornithine carbamoyltransferase activity, N-acetylglutamate levels or O2 uptake with succinate. We also performed a kinetic study of citrulline synthesis as a function of ornithine concentration. We found increased Km values for ornithine and varied Vmax values of citrulline synthesis, which suggested the presence of a mutant transport protein. From these results we conclude that the defect of hyperornithinemia, hyperammonemia and homocitrullinuria lies in the transport of ornithine across the mitochondrial membrane.
authors.affiliation: Department of Biochemistry, Faculty of Medicine, Kagoshima University, Japan.
authors.forename: I
authors.initials: I
authors.lastname: Inoue
authors.forename: T
authors.initials: T
authors.lastname: Saheki
authors.forename: K
authors.initials: K
authors.lastname: Kayanuma
authors.forename: M
authors.initials: M
authors.lastname: Uono
authors.forename: M
authors.initials: M
authors.lastname: Nakajima
authors.forename: K
authors.initials: K
authors.lastname: Takeshita
authors.forename: R
authors.initials: R
authors.lastname: Koike
authors.forename: T
authors.initials: T
authors.lastname: Yuasa
authors.forename: T
authors.initials: T
authors.lastname: Miyatake
authors.forename: K
authors.initials: K
authors.lastname: Sakoda
mesh_terms: D000592:Amino Acid Metabolism, Inborn Errors / Q000378:metabolism*; D000641:Ammonia / Q000378:metabolism*; D001692:Biological Transport; D002956:Citrulline / Q000031:analogs & derivatives* / Q000096:biosynthesis / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D008930:Mitochondria, Liver / Q000378:metabolism*; D009952:Ornithine / Q000378:metabolism*
chemical_list: C001352:homocitrulline; D002956:Citrulline; D000641:Ammonia; D009952:Ornithine