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Biomedical subjects

E Huber

Publications and source records attributed to E Huber.

At least 73 records · Page 4Linked to original sources
PubMed1978

Determination of microsomal UDP-glucuronyltransferase in needle-biopsy specimens of human liver.

Sensitive, reliable and convenient assays are described for the study of human liver microsomal UDP-glucuronyltransferase. Using 14C-1-naphthol as substrate about 2 mg of a liver biopsy specimen and for 14C-morphine about 20 mg of tissue will suffice for enzyme estimation. Lack of inhibition of 1-naphthol glucuronidation by morphine suggests that the substrates are glucuronidated by different forms of the enzyme. Enzyme levels in the native and activated state were studied in biopsies from patients grouped according to histopathological and clinical criteria. The enzyme assays may help to characterize UDP-glucuronyltransferases in human tissues and their induction by drugs and environmental chemicals, as well as their alteration in various diseases.

Animals↗
PubMed1978

A characterization of the nucleotide uptake of chromaffin granules of bovine adrenal medulla.

Chromaffin granules isolated from bovine adrenal gland were incubated with (3)H-labelled nucleotides and [(14)C]noradrenaline to study the uptake of these substances. [(3)H]ATP, [(3)H]ADP and [(3)H]AMP are taken up by these organelles by the same temperature-dependent mechanism. The apparent K(m) for ATP and ADP is 1.4mm, and for AMP it is 2.9mm. The uptake of ATP has a flat pH optimum, whereas the catecholamine uptake increases with more alkaline pH. Atractyloside and carboxyatractyloside are competitive and specific inhibitors of nucleotide uptake, whereas reserpine inhibits only that for catecholamines. Mg(2+) ions activate uptake of both catecholamine and nucleotides, whereas EDTA and N-ethylmaleimide inhibit these processes. Nucleotide and catecholamine uptakes are inhibited by uncouplers of oxidative phosphorylation and by two ATP analogues. NH(4) (+) ions and nigericin in the presence of KCl inhibit only catecholamine uptake. It is concluded that nucleotide uptake, as proposed previously for catecholamine uptake, depends on an electrochemical proton gradient produced by a proton-translocating adenosine triphosphatase localized in the membrane of chromaffin granules. Furthermore, as suggested by the effect of NH(4) (+) and nigericin, catecholamine uptake apparently depends on the chemical part of this gradient, whereas the results for nucleotide uptake are consistent with its dependence on the electrical component.

Adenosine Diphosphate↗
PubMed1977

UDP-glucuronyltransferase in perfused rat liver and in microsomes. Effects of CCl4 injury.

To elucidate the disparity between glucuronidation rates in vivo and UDP-glucuronyltransferase in vitro after CCl4 injury, the time course of the effects of CCl4 (0.25 ml/kg) on kinetic properties of UDP-glucuronyltransferase (l-naphthol as substrate) was examined in rat liver homogenates and microsomes. These experiments were compared with l-naphthol glucuronidation by the perfused liver which was studied at various time points after CCl4 administration. Phenobarbital-treated rats were used to enhance the hepatotoxicity of CCl4. 1. Within 24 h UDP-glucuronyltransferase activity increased 8-fold in liver homogenates and 3-fold in microsomes. During this time the allosteric activator, UDP-N-acetylglucosamine, lost its effect whereas the inhibitor UPD showed greater inhibitory properties, thus counteracting the activation. 2. l-Naphthol glucuronidation in perfused livers was significantly decreased by 24 h. Sulfate ester formation was little affected. 3. The content of UDP-glucuronic acid was not significantly altered although liver histology revealed about 45% necrotic and prenecrotic cells and an uniform fatty degeneration of hepatocytes after 24 h. The results suggest that during CCl4 injury, UDP-glucuronyltransferase is activated. At the same time the kinetic properties of the enzyme are altered in a way leading to inefficient glucuronide synthesis, when assays are carried out under conditions presumed to exist in vivo. Nevertheless the capacity to form glucuronides is retained in the acutely injured liver.

Animals↗