Search PubMed⌕ Search

Biomedical subjects

T Saheki

Publications and source records attributed to T Saheki.

At least 163 records · Page 9Linked to original sources
PubMed1982

Argininosuccinate synthetase activity in cultured skin fibroblasts of citrullinemic patients.

The activities and kinetic properties of argininosuccinate synthetase in cultured skin fibroblasts of three citrullinemic patients with qualitative or quantitative abnormalities of hepatic argininosuccinate synthetase were examined. The cultured skin fibroblasts of a citrullinemic patient with a low hepatic argininosuccinate synthetase activity showed low activity and abnormal kinetics similar to those of the hepatic enzyme. This suggests a similar genetic origin of the fibroblast argininosuccinate synthetase as of the hepatic enzyme. However, we found normal argininosuccinate synthetase activity in cultured fibroblasts of two citrullinemic patients who had a low hepatic enzyme activity resulting from decrease in the amount of enzyme protein but with normal kinetic properties. This suggests that part of the quantitative abnormality of hepatic argininosuccinate synthetase of citrullinemic patients may be due to an abnormal organ-specific gene expression in the liver.

Adolescent↗
PubMed1982

Intracellular distribution and biosynthesis of lipoamide dehydrogenase in rat liver.

Lipoamide dehydrogenase (LADase) was purified to homogeneity from rat liver mitochondria, and the intracellular distribution and biosynthesis of the LADase were investigated with antibody prepared against the purified enzyme. 1) LADase activity was mostly found in mitochondria; the activity in cytosol was about one-tenth of that in mitochondria. 2) LADase in the crude mitochondrial and cytosolic extracts and the purified LADase were immunologically identical as judged from the Ouchterlony double diffusion test. These LADases were indistinguishable from each other on immunochemical titration; i.e., the amount of LADase precipitated by a fixed amount of the anti-LADase antibody was the same for all the preparations. However, cytosolic LADase activity was inhibited by the antibody more strongly than mitochondrial LADase activity. 3) Two min after intravenous injection of [35S]methionine, more radioactivity was incorporated into cytosolic LADase than into the mitochondrial enzyme in the liver. This result suggests that localization of LADase in the cytosolic fraction is not an artifact due to leakage from mitochondria during homogenization of rat liver. 4) LADase was synthesized predominantly on free ribosomes, which indicates that LADase is synthesized on cytoplasmic ribosomes and translocated into mitochondria just as other mitochondrial proteins are. 5) After cell-free protein synthesis with post-mitochondrial supernatant, radioactivity immunoprecipitated with anti-LADase antibody was detected as a major peak with the same molecular weight as the purified LADase.

Animals↗
PubMed1982

Diurnal fluctuation of blood ammonia levels in adult-type citrullinemia.

A 48-year-old man, who was diagnosed as adult-type citrullinemia by quantitative estimation of urea cycle enzymes in the liver, showed a regular nocturnal rise of blood ammonia level. In order to elucidate the mechanism of diurnal fluctuation of blood ammonia level, the patient was put into fasting state for four days. The blood ammonia level rose at the night of the first fasting day even though no food was taken, then it decreased gradually and reached the lowest level in the morning of the third fasting day. Intravenous administration of amino acids mixture under the same starved condition gave rise to a significant elevation of blood ammonia level. Based on these results, it was concluded that hyperammonemia of adult-type citrullinemia could result from the accumulation of free ammonia which was produced from the catabolism of amino acids absorbed from the small intestine and surpassed the urea synthesis of defective urea cycle to flood into the blood. Furthermore, the rise of blood ammonia level at the night of the first fasting day suggested that the circadian rhythm of amino acid-carbohydrate metabolism might superimpose on the process mentioned above.

Amino Acids↗
PubMed1981

Qualitative and quantitative abnormalities of argininosuccinate synthetase in citrullinemia.

Enzymological and immunochemical analyses of the liver were preformed in seven Japanese patients with citrullinemia. Among the urea cycle enzymes in the liver, only the activity of argininosuccinate synthetase was specifically decreased to 2 to 50% of normal controls. Liver argininosuccinate synthetase of patients was indistinguishable from that of controls when tested immunochemically by Ouchterlony's double immunodiffusion technique with anti-rat argininosuccinate synthetase antiserum. Immunochemical analysis by means of the single radial immunodiffusion revealed that the decrease in the activity of liver argininosuccinate synthetase was explainable by a decrease in the amount of the enzyme protein in five patients, while the decrease in the activity in the other two patients was not accompanied by a decrease of enzyme protein. The Km values for the substrates of liver argininosuccinate synthetase of the former five were similar to those of the control, while the kinetic properties of the latter two were quite different in terms of higher Km values and negative cooperativity. From these results, we consider that citrullinemia may consist of more than one type including qualitative or quantitative abnormalities of argininosuccinate synthetase caused by some defects in certain genes or in the epigenetic processes in the liver.

Adolescent↗
PubMed1981

Treatment of adult-type citrullinemia with administration of citrate.

A 48-year-old man who showed a regular diurnal fluctuation of blood ammonia level was diagnosed as adult-type citrullinemia with quantitative estimation of plasma amino acids and urea cycle enzymes in the liver. The restriction of daily protein intake less than 50 g and oral administration of lactulose had no effect on the blood ammonia level. The efficacy of four amino acid solutions which had been used in order to improve the hepatic encephalopathy was compared each other in this case. Glutamate-arginine mixture had the same effect as glutamate solution in lowering the blood ammonia level, and glutamate was thought to be essential. Also, oral administration of citrate showed a remarkable effect almost comparable to intravenous administration of glutamate. Analysis of plasma amino acids 3 hr after citrate administration demonstrated an increase in glutamate and a decrease in citrulline. These observations suggest that a metabolic pathway of citrate-alpha-ketoglutarate-glutamate-glutamine takes part in disposing free ammonia in the blood.

Amino Acids↗
PubMed1981

Comparison of argininosuccinate synthetase from young and old rat livers.

Properties of argininosuccinate synthetases (ASS), including immunological properties and heat stability, from young and old rats were quite similar. However the degradation rates of ASS from young and old rats were found to be different as shown in the experiment using the double labeling technique. Three forms of this enzyme from young and old rat livers were separated by DEAE-Sephadex A-50 column chromatography, and they were called ASS 1, 2 and 3 in order of elution. The degradation rate of ASS 1 from young and old rat livers was very similar, but the rate of degradation of ASS 2 form old rat livers was greater than that from young rat livers.

Aging↗
PubMed1980

Comparison of the urea cycle in conventional and germ-free mice.

The urea cycle in the liver of conventional mice was compared with that of germ-free mice. Among the urea cycle enzymes and urea cycle-related substances, only ornithine in the liver of the conventional mice was markedly more abundant than in that of the germ-free mice. The significance of this finding was supported by the comparison of the urea synthesis in the liver slices from these two types of mice.

Animals↗
PubMed1979

Studies on rat liver argininosuccinate synthetase. Inhibition by various amino acids.

Inhibition studies of crystallized rat liver argininosuccinate synthetase [EC 6.3.4.5] are described. 1. L-Argininosuccinate, L-histidine, and L-tryptophan inhibited the enzyme activity at saturating amounts of the substrates. 2. L-Norvaline, L-argininosuccinate, L-arginine, L-isoleucine, and L-valine competitively inhibited the enzyme activity at a low concentration of L-citrulline, with Ki values of 1.3 x 10(4) M, 2.5 X 10(-4) M, 6.7 X 10(-4) M, 6.3 X 10(-4) M, and 6.0 x 10(-4) M, respectively. 3. L-Argininosuccinate and L-arginine competitively inhibited the enzyme activity at a low concentration of L-aspartate, with Ki values of 9.5 x 10(-4) M and 1.2 x 10(-3) M, respectively. 4. The modes of inhibition by L-histidine were mixed-noncompetitive, uncompetitive, and noncompetitive types with respect to L-citrulline, L-aspartate, and ATP, respectively. 5. When the enzyme was preincubated with L-citrulline, the enzyme activity was slightly increased in the presence of a low concentration of L-histidine in the assay mixture. 6. The conformation of the enzyme was markedly changed by the addition of L-histidine as judged from the CD spectrum. This change was partially reversed by incubation with L-citrulline.

Amino Acids↗