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Biomedical subjects

J K Parks

Publications and source records attributed to J K Parks.

46 records · Page 3Linked to original sources
PubMed1982

Friedreich ataxia: III. Mitochondrial malic enzyme deficiency.

Polarographic assays of oxidative phosphorylation in muscle mitochondria indicated abnormal pyruvate-malate metabolism in Friedreich ataxia (FA). Pursuing this clue, more specific assays were performed. Mitochondrial malic enzyme (MEm; malate: NADP+ oxidoreductase) specific activity was 10% of controls in fibroblasts from eight FA patients (p less than 0.0001). Cytosolic malic enzyme was modestly increased in FA fibroblasts. Mitochondrial and cytosolic malate dehydrogenase and aspartate aminotransferase, and malate transport on the dicarboxylate and alpha-ketoglutarate carriers were normal in fibroblasts or leukocytes. MEm activity is normally highest in the nervous system and heart is important in regulating carbohydrate metabolism. MEm deficiency could cause FA; further studies are required to substantiate this hypothesis.

Cytosol↗
PubMed1981

Inhibitory effects of sodium valproate on oxidative phosphorylation.

Sodium valproate (VP) inhibited oxidative phosphorylation in isolated rat liver mitochondria. State 3 rates of oxygen consumption with glutamate as substrate were 80% of control values at a low VP concentration (24 microM). At 240 microM, there was more than 50% inhibition of glutamate and alpha-ketoglutarate state 3 rates. Succinate state 3 rates were 80% of control values, and uncoupling was noted at 2400 microM VP. These VP effects were similar to those of propionate and isovalerate, suggesting a common mechanism of toxicity. Inhibition of mitochondrial oxidative phosphorylation may explain why VP intoxication causes a hepatocerebral disorder that resembles Reye syndrome.

Animals↗
PubMed1980

Propionate inhibition of succinate:CoA ligase (GDP) and the citric acid cycle in mitochondria.

Propionate inhibits oxygen consumption by rat liver mitochondria when glutamate, alpha-ketaglutarate, and succinate are substrates. Carnitine prevents this effect. The pattern of inhibition of 14CO2 release from metabolic intermediates indicates citric acid cycle inhibition between succinate:coenzyme A (CoA) ligase (GDP) and malate dehydrogenase. Propionyl CoA is synthesized from propionate in mitochondria. Propionyl CoA is a potent inhibitor of succinate:CoA ligase with positive cooperativity and half half-maximal inhibition at 2 X 10(-4) M propionyl CoA.

Acyl Coenzyme A↗
PubMed1980

Urea cycle regulation: I. Coupling of ornithine metabolism to mitochondrial oxidative phosphorylation.

Ornithine metabolism is coupled to oxidative phosphorylation in isolated rat liver mitochondria. The pathway involving ornithine: alpha-ketoglutarate transaminase (OKT), glutamic semialdehyde dehydrogenase (GSDH), and glutamate dehydrogenase (GDH) with cycling of alpha-ketoglutarate-glutamate at the OKT reaction appears to be involved. Ornithine may be utilized by this pathway to sustain ATP levels during mitochondrial energy-deficiency states with resultant decreased urea-cycle flux and increased ammonia production. This pathophysiologic mechanism suggests that hyperammonemia is a consequence of an energy-deficiency state. Therapy directed toward alleviating the energy-deficiency state may be more beneficial than efforts to reduce ammonia levels.

Adenosine Triphosphate↗
PubMed1979

Friedreich ataxia. II. Normal kinetics of lipoamide dehydrogenase.

Lipoamide dehydrogenase (LAD) kinetic values, Km and Vmax, were normal in 11 patients with Friedreich ataxia. Fibroblast activities of the pyruvate and alpha-ketoglutarate dehydrogenase complex, and LAD activities, were also normal. There was no reduction in oxidative decarboxylation of pyruvate, alpha-ketoglutarate, or several other substrates in intact fibroblasts. Methodologic differences may account for differences of opinion about putative abnormalities of the alpha-ketoacid dehydrogenase complexes.

Adolescent↗
PubMedDate not supplied

Cytochrome oxidase inhibition: a novel animal model of Alzheimer's disease.

A profound decrease in activity of the mitochondrial enzyme cytochrome oxidase in blood platelets is a recently identified concomitant of Alzheimer's disease (AD). We investigated a possible pathogenic link between this finding and the symptoms of AD by mimicking this mitochondrial enzyme deficiency in rats. Rats were infused chronically with a selective inhibitor of cytochrome oxidase, sodium azide, or with saline delivered via subcutaneously implanted osmotic minipumps. The azide treatment impaired both spatial and nonspatial learning. Further, the azide treatment inhibited a low-threshold form of hippocampal long-term potentiation, primed burst potentiation. The behavioral deficits were not secondary to a sensory or motor impairment. Thus, chronic azide treatment of rats models some characteristics of AD.

Alzheimer Disease↗