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At least 145 records · Page 8Linked to original sources
PubMed1977

L-Ornithine-ketoacid-transaminase deficiency in cultured fibroblasts of a patient with hyperornithinaemia and gyrate atrophy of the choroid and retina.

L-Ornithine-ketoacid-transaminase deficiency was established in cultured fibroblasts obtained from a patient with hyperornithinaemia (mean ornithine level in serum approximately 100 mumol/l) and gyrate atrophy of the choroid and retina. The deficiency was found both the L-ornithine concentrations of 3.0 mM (about twice the KM value) and 12 mM, indicating that the enzymic defect was not due to a decreased affinity for this substrate. The reliability of the colorimetric assay of ornithine-ketoacid-transaminase activity was established radiochemically. Performance of the radiochemical assay revealed the presence of an impurity in the substrate DL-[2-14C]ornithine - HCl being a strong inhibitor of the enzyme. The passage level and the subcultivation time of the fibroblasts did not influence the enzymic activity.

Amino Acids↗
PubMed1983

Free amino acid concentrations in blood cells of two brothers with gyrate atrophy of the choroid and retina with hyperornithinaemia.

In this study we selected blood cells as accessible tissues and measured the free amino acid concentrations in erythrocytes, lymphocytes, and granulocytes of two patients with gyrate atrophy with hyperornithinaemia. We found that ornithine concentrations were elevated in blood cells, to different degrees depending on the type of cell, and that aspartic acid concentrations were low in erythrocytes. We also investigated the fluctuation of free amino acid concentrations in blood cells up to 24 h after the oral administration of ornithine. The ornithine concentration in the blood cells of the patients reached a peak 2 h after the oral administration, and remained high for at least 4 h, although after 2 h the concentration curves differed in the three types of cells.

Adult↗
PubMed1983

Simulation of the conditions of gyrate atrophy in vitro suppresses retinal protein synthesis.

The effect of ornithine on retinal protein synthesis was evaluated using isolated baboon retinas maintained in vitro. When ornithine was present in the culture medium at a concentration equivalent to the plasma level of ornithine in gyrate atrophy patients (1 mM), the incorporation of 3H-leucine was reduced to 70 per cent of control levels. Progressively higher concentrations of ornithine resulted in a further suppression of protein synthesis. Soluble radioactivities after short incubation times from control and ornithine cultured retina were similar indicating no effect of ornithine on uptake of 3H-leucine. Grain counts in autoradiographs of control and ornithine-treated retinas revealed a suppression of incorporation in all retinal strata. These results suggest that elevated ornithine levels may suppress ongoing protein synthesis in the retina.

Animals↗
PubMed1984

Gyrate atrophy of the choroid and retina: decreased ornithine aminotransferase concentration in cultured skin fibroblasts from patients.

A sensitive and convenient radioisotopic assay for ornithine aminotransferase (OAT) and an enzyme immunoassay for human ornithine aminotransferase were developed for studying decrease in activity of this enzyme in gyrate atrophy of the choroid and retina with hyperornithinemia. Picogram amounts of human OAT could be detected by the enzyme immunoassay. The OAT activity in cultured fibroblasts from two patients was 6% and 2% of that in control fibroblasts, and did not increase on addition of a high concentration of vitamin B6. The decreased activity, assayed by enzyme immunoassay, was associated with decreased enzyme concentration, suggesting that deficiency of OAT in these patients is not due to production of a structurally altered enzyme lacking catalytic activity, but to decreased production of enzyme protein. When cells from patients were repeatedly subcultured, selective loss of both the activity and concentration of OAT was observed, without changes in activities of several other enzymes tested.

Atrophy↗
PubMed1988

The ornithine aminotransferase (OAT) locus: analysis of RFLPs in gyrate atrophy.

A cDNA probe (HOAT1) for ornithine aminotransferase (OAT) has recently been used to map (1) the structural gene for this enzyme to chromosome 10 and (2) several related DNA sequences to the X chromosome. We have defined six RFLPs for OAT, to explore its possible role in gyrate atrophy (GA) of the choroid and retina, an autosomal recessive genetic disorder associated with a deficiency of OAT activity. The RFLPs, which are detected by noncoding single-copy probes from the OAT gene and by subclones of the HOAT1 cDNA, all map on human chromosome 10, producing an overall level of heterozygosity for the OAT locus of 83%. Using the RFLPs, we have determined that the OAT locus segregates concordantly with GA in one available pedigree. Furthermore, the RFLPs display significant disequilibrium with GA, providing genetic evidence implicating a defect in the OAT structural gene as the cause of this disorder. The RFLPs for OAT are potentially applicable to prenatal diagnosis and carrier detection in families with a previous history of GA. They will also allow identification of specific haplotypes associated with GA chromosomes, as a guide for more detailed molecular-genetic investigations of the mutations underlying the disorder.

Cell Line↗
PubMed1981

Gyrate atrophy of the choroid and retina in a cat.

An adult male, domestic short-haired cat with generalized retinal atrophy was found to have a 60-fold increase in plasma ornithine and ornithinuria. Ornithine-8-aminotransferase activity was undetectable in its tissues and in its cultured skin fibroblasts. This feline condition is thus analogous to gyrate atrophy of the choroid and retina in humans.

Amino Acid Metabolism, Inborn Errors↗