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Biomedical subjects

C K Kurup

Publications and source records attributed to C K Kurup.

At least 37 records · Page 2Linked to original sources
PubMed1987

Effect of administration of diethylhexyl phthalate on the function and turnover of rat hepatic mitochondria.

Administration of the widely used plasticizer di(2-ethylhexyl)phthalate (2% w/w) in the diet to the rat caused proliferation of mitochondria in the liver. The number of mitochondria as well as the amount of protein recovered in the organellar fraction was doubled. Mitochondria isolated from the livers of treated animals showed decreased (50%) respiratory activity. The content and activity of cytochrome oxidase were also decreased. The specific incorporation of amino acids into the proteins of whole liver and of mitochondria was not increased in plasticizer-treated animals. Isolated mitochondria also did not show any difference in the rate of incorporation of amino acids into proteins. The half-lives of whole liver proteins and of mitochondria were increased in plasticizer-fed animals. The half-life of cytochrome oxidase, however, was unaffected by the treatment. The pattern of double labeling of mitochondrial proteins confirmed decreased turnover in plasticizer-treated animals.

Amino Acids↗
PubMed1987

Hypocholesterolemic action of 1-ethoxysilatrane.

Intraperitoneal administration of the organosilicon compound 1-ethoxysilatrane to the rat caused a 25% decrease in the concentration of cholesterol in serum without affecting that of triacylglycerols. The specific activity of 3-hydroxy-3-methylglutaryl CoA reductase, the rate-limiting enzyme in cholesterol biosynthesis, was depressed in hepatic microsomes of silatrane-treated animals.

Animals↗
PubMed1987

Vanadate-stimulated NADH oxidation in microsomes.

Addition of vanadate, stimulated oxidation of NADH by rat liver microsomes. The products were NAD+ and H2O2. High rates of this reaction were obtained in the presence of phosphate buffer and at low pH values. The yellow-orange colored polymeric form of vanadate appears to be the active species and both ortho- and meta-vanadate gave poor activities even at mM concentrations. The activity as measured by oxygen uptake was inhibited by cyanide, EDTA, mannitol, histidine, ascorbate, noradrenaline, adriamycin, cytochrome c, Mn2+, superoxide dismutase, horseradish peroxidase and catalase. Mitochondrial outer membranes possess a similar activity of vanadate-stimulated NADH oxidation. But addition of mitochondria and some of its derivative particles abolished the microsomal activity. In the absence of oxygen, disappearance of NADH measured by decrease in absorbance at 340 nm continued at nearly the same rate since vanadate served as an electron acceptor in the microsomal system. Addition of excess catalase or SOD abolished the oxygen uptake while retaining significant rates of NADH disappearance indicating that the two activities are delinked. A mechanism is proposed wherein oxygen receives the first electron from NAD radical generated by oxidation of NADH by phosphovanadate and the consequent reduced species of vanadate (Viv) gives the second electron to superoxide to reduce it H2O2. This is applicable to all membranes whereas microsomes have the additional capability of reducing vanadate.

Animals↗
PubMed1987

NADH-dependent polyvanadate reduction by microsomes.

NADH-dependent reduction of polyvanadate was observed by using rat liver microsomes as the enzyme source. The reduced vanadate form obtained was blue in color with a broad absorption maximum in the red region around 650 nm. Microsomes and phosphate anions were found to be essential for polyvanadate reduction. The rate and the extent of formation of blue color compound was dependent on the amount of vanadate present. Cytochrome b5 was found to be involved in this SOD-insensitive reaction. The rate of disappearance of the blue-colored compound was dependent on concentration of NADH and was found to be sensitive to SOD. Catalase and Mn2+, which inhibit oxygen consumption accompanying NADH oxidation, increased both the rate and extent of the blue color compound formed. The results suggest that vanadate acts as an electron acceptor.

Animals↗
PubMed1987

Generation of hydrogen peroxide by brown adipose tissue mitochondria.

This is the first report on the generation of H2O2 by brown adipose tissue mitochondria. Flavin dehydrogenase-linked substrates like succinate, glycerol-1-phosphate, and fatty acyl CoA were good substrates for the reaction, while NAD+-linked substrates were less effective. In cold-acclimated animals the activity showed a substantial increase (2.5-fold). The Km and Vmax of the reaction were considerably lower than those of the respective dehydrogenase. Metal ions, particularly Cu2+ and Fe2+ were potent inhibitors of the reaction. Nucleoside diphosphates, which were inhibitors by themselves, potentiated the inhibitory action of Fe2+ ions. In most of the properties, the H2O2 generator of brown adipose tissue mitochondria resembled that of liver mitochondria.

Adipose Tissue, Brown↗
PubMed1986

Reduction of vanadate by a microsomal redox system.

The reduction of vanadate catalyzed by rat liver microsomes is demonstrated. This reaction is SOD-insensitive. It is specific for NADH and polyvanadate and is not obtained with metavanadate and NADPH.

Animals↗
PubMed1986

Investigations on the mechanism of the hypocholesterolemic action of diethylhexyl phthalate in rats.

The plasticizer di(2-ethylhexyl)phthalate (DEHP), used widely in the manufacture of food packages and medical plastic devices, depressed serum cholesterol (40%) and proliferated hepatic mitochondria (100%) when administered in the diet (2%, w/w) to the rat. Microsomes isolated from the livers of animals administered DEHP showed lowered specific activity of 3-hydroxy-3-methyl glutaryl coenzyme A reductase (50%). The incorporation of acetate but not of mevalonate into hepatic cholesterol was decreased (52%) in these animals. The release of bile acids was greatly enhanced (100%), and the activity of cholesterol 7 alpha-hydroxylase, the regulatory enzyme in the pathway of bile acid formation, was stimulated (70%) on DEHP administration. Even though the capacity of mitochondria to oxidize the side chain of cholesterol was not enhanced in DEHP-fed animals, the larger population of mitochondria would ensure that the amount of cholesterol oxidized per gram of liver was significantly higher.

Acetates↗
PubMed1986

Effect of lutein on the transport of Ca2+ across phospholipid bilayer and mitochondrial membrane.

Lutein (3,3'-dihydroxy alpha-carotene), a xanthophyll present in plant chloroplasts, increases the permeability of phospholipid vesicles to Ca2+, even though the pigment does not bind the metal ion. Energy-dependent uptake of Ca2+ by mitochondria is inhibited by lutein, which permits a rapid efflux of the ion from Ca2+-loaded mitochondria. These results are consistent with the view that the deleterious action of lutein on mitochondrial oxidative phosphorylation results from its destabilizing action on membrane structure.

Animals↗
PubMed1985

Effect of administration of 2-methyl-4-dimethylaminoazobenzene on the half-lives of rat liver mitochondria and cytochrome oxidase.

The turnover of total mitochondrial proteins and cytochrome oxidase in the livers of rats administered with 2-methyl-4-dimethylaminoazobenzene (2-Me-DAB) has been determined. The incorporation of [14C]bicarbonate revealed a half-life of 3.1 days in control and 6 to 9 days in azodye administered animals for whole mitochondrial proteins. The incorporation of [35S]methionine yielded t1/2 values of 8.5 days and 15.4 days, respectively. The t1/2 of cytochrome oxidase, 10.8 days for control and 19.3 days for 2-Me-DAB-treated animals, indicated that the delay in the decay of the enzyme was of the same order as that of whole mitochondria. Short term incorporation revealed that the administration of the azodye stimulated the synthesis of the enzyme. Mitochondria isolated from azodye-administered animals appeared less susceptible to lysosomal proteolysis. Also, azodye administration seemed to impair the ability of lysosomes to degrade mitochondria.

Animals↗
PubMed1985

Effect of parthenin on mitochondrial oxidative phosphorylation.

The sesquiterpene lactone, 'parthenin' the toxic principle of the allergenic weed Parthenium hysterophorus, inhibited 'state 3' respiration and stimulated 'state 4' respiration in rat liver and kidney mitochondria as well as ATPase activity in the presence of Mg2+ ions. These properties indicate that the toxic action of parthenin may be related to its interference with oxidative phosphorylation.

Adenosine Triphosphatases↗
PubMed1984

Functional changes in rat liver mitochondria on administration of 2-methyl-4-dimethylaminoazobenzene.

Administration of 2-methyl-4-dimethylaminobenzene in the diet (0.1%, w/w) for 85-90 days doubled the content of mitochondria in the livers of rats. The azodye was covalently bound to liver proteins, and about 15% of the amount found in liver was associated with the mitochondrial fraction. Mitochondria isolated from the livers of azodye-fed animals showed drastically lowered ability to oxidize NAD+-linked substrates. The inhibited electron-transfer step was the reduction of ubiquinone. The organelles showed a large increase in succinate oxidase activity. The activity of cytochrome oxidase and the content of cytochrome aa3 were substantially higher in these organelles. Azodye-fed animals showed depressed serum cholesterol concentrations. The content of ubiquinone in liver also registered a small increase.

Animals↗
PubMed1984

Inhibition of mitochondrial oxidative phosphorylation by 2-methyl-4-dimethylaminoazobenzene.

The azodye 2-methyl-4-dimethylaminoazobenzene inhibited oxidation and phosphorylation in tightly coupled rat liver mitochondria. Phosphorylation was more sensitive to the inhibitory action of the azodye than was the oxidation of succinate or ascorbate. The oxidation of NAD+-linked substrate was severely inhibited by the compound. In submitochondrial particles, only NADH oxidation was sensitive. The site of inhibition has been identified to lie between the dehydrogenase flavoprotein and ubiquinone.

Animals↗
PubMed1984

Influence of ubiquinone on the inhibitory effect of adriamycin on mitochondrial oxidative phosphorylation.

The inhibition of succinate oxidation in both heart and liver mitochondria by the cardiotoxic anticancer antibiotic adriamycin in vitro was reversed to a large extent by exogenous ubiquinone-45. Inhibition of the oxidation of NAD+-linked substrates in heart and liver mitochondria responded differently to ubiquinone, the inhibition being reversed only in liver organelles. Administration of adriamycin inhibited oxidative phosphorylation in rat heart, kidney and liver mitochondria, the inhibition being highest in the heart organelles (about 50% for both NAD+-linked substrates and succinate). Exogenous addition of ubiquinone to mitochondria isolated from drug-treated animals did not reverse the inhibition. Administration of ubiquinone along with adriamycin did not change effectively the pattern of drug-mediated decrease in oxidative activity of the organelles, particularly in the heart.

Animals↗
PubMed1984

Oxidations in kidney mitochondria of heat-exposed rats: regulation by cytochrome c.

Exposure of rats to higher environmental temperature (36-37 degrees C) decreased the capacity of their kidney mitochondria to oxidize succinate. The decrease was corrected on the addition of exogenous cytochrome c. Kidney mitochondria of heat-exposed animals showed decreased rates of H2O2 generation when alpha-glycerophosphate, but not succinate, was used as electron donor. These mitochondria also showed decreased activity of alpha-glycerophosphate dehydrogenase but not of succinate dehydrogenase. The content of cytochrome c in kidney mitochondria of heat-exposed animals was low even though the concentration of the pigment in the whole tissue did not decrease. Starvation as well as administration of an antithyroid agent like propylthiouracil simulated some of the effects of heat exposure on kidney mitochondria, but the cytochrome c-dependent reversal of inhibition of oxidation was obtained only in heat exposure.

Animals↗