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Biomedical subjects

W Kunz

Publications and source records attributed to W Kunz.

At least 127 records · Page 7Linked to original sources
PubMed1979

Vinyl chloride and trichloroethylene: comparison of alkylating effects of metabolites and induction of preneoplastic enzyme deficiencies in rat liver.

[1,2-14C] Vinyl chloride and [1,2-14C] trichloroethylene were incubated with rat liver microsomes, NADPH and RNA (from yeast). Whereas trichloroethylene metabolites were irreversibly bound to proteins in microsomal incubations to a higher extent than vinyl chloride metabolites, irreversible binding to RNA was lower for trichloroethylene metabolites. Hydrolysis of the RNA which was reisolated from microsomal incubations with 14C-vinyl chloride or 14C-trichloroethylene and separation of the nucleosides showed different alkylation products arising from vinyl chloride and from trichloroethylene, characteristic for vinyl chloride being formation of 1,N6-ethenoadenosine and 3,N4-enthenocytidine. The different reactivities of metabolites of vinyl chloride and of trichloroethylene prompted a comparison of the oncogenic effects of both compounds against the rat liver cell. Newborn rats were exposed for 10 weeks to 2000 ppm vinyl chloride or trichloroethylene (8 h/day; 5 days/week). After this period livers of the animals were stained for nucleoside-5-triphosphatase. Whereas the vinyl chloride exposed rats showed focal hepatocellular deficiencies in this enzyme, which are supposed to represent an early sign of malignancy, no such changes were induced by trichloroethylene exposure. The data therefore suggest differences between the hepatocarcinogenic activity of vinyl chloride and possible effects of trichloroethylene on the liver.

Adenosine↗
PubMed1979

Influences of inducers and inhibitors of the microsomal monooxygenase system on the alkylating intensity of dimethylnitrosamine in mice.

Male mice were pretreated with various drugs, which are known either induce or to inhibit cytochrome P 450 function. Five hours after the administration of 14C-dimethylnitrosamine (10 mg/kg) in pretreated and control mice, total and specific radioactivities of cellular macromolecules of the liver were determined. Various types of nucleic acids were extracted and hydrolyzed, and the bases and nucleotides separated by ion-exchange-chromatography. Radioactivity resulting from incorporation and alkylation was measured. Pretreatment of mice with the inducers phenobarbital and 3-Methylcholanthrene decreased the alkylation rates, while administration of the inhibitors SKF 525 A and CFT 1201 caused an increase. These results appear to contradict the accepted activation mechanism of nitrosamines if DMN demethylation as catalyzed by cyt. P 450 is influenced in the same way as other cyt. P 450 dependent reactions.

Alkylation↗
PubMed1979

Binding of nitrosamines to cytochrome P-450 of liver microsomes.

The interactions of 5 carcinogenic and 1 non-carcinogenic nitrosamines with hepatic microsomal cytochrome (cyt.) P-450 were investigated, using both optical difference and electron paramagnetic resonance (EPR) spectroscopic methods. Liver microsomes from phenobarbital (PB)-pretreated mice and 3-methylcholanthrene (3-MC)-pretreated rats were used, in order to have an increased specific content of cyt. P-450 and cyt. P-448 respectively. The optical and EPR spectral data obtained in the oxidised state suggest that nitrosamines are able to bind both as substrates and as ligands to the hemoprotein cyt. P-450, depending on the concentration of nitrosamine, its chemical identity and the cytochrome species present. After reduction with dithionite or NADPH in the optical difference spectrum a Soret band developed between 444 and 453 nm to an extent, which is dependent on the particular nitrosamine present. This initial nitrosamine-induced spectrum might represent a ferrous nitric oxide (NO)-cyt. P-450 complex. It appears unstable and is converted kinetically into a spectrum lacking a Soret band, but with a predominant absorbance minimum at about 425 nm. A visible band is located at 585 nm. In the EPR spectrum a sharp 3-line signal around g = 2.01 appears concomitantly. Both spectral parameters are typical of a NO-cyt. P-420 complex. These results, in conjunction with metabolic studies, indicate that nitrosamines are denitrosated by a reductive process in which cyt. P-450 appears to be involved. The resulting NO-cyt. P-450 complex denatures to a NO-cyt. P-420 complex when the dioxygen level is not sufficiently high to complete successfully.

Animals↗
PubMed1979

DNA damage induced in vivo evaluated with a non-radioactive alkaline elution technique.

A modification of the alkaline filter elution test was used to study damage to liver DNA of NMRI mice following in vivo treatment with various hepatocarcinogens and drugs causing liver enlargement. Liver cell nuclei were prepared and lysed on top of polyvinyl filters. DNA was eluted, and the amounts both remaining on the filter and in the eluate were measured colorimetrically. Dimethylnitrosamine (DMN), diethylnitrosamine (DEN), N-nitrosomorpholine and methyl methanesulfonate (MMS) caused significant enhancement of DNA passage through the filters, whereas N-acetylaminofluorene (AAF), 4-dimethylaminoazobenzene (DAB), phenobarbital, halothane and CCl4 did not. The applicability of this short term test is discussed.

Animals↗
PubMed1978

Influence of Mg2+-ions on the properties of rat heart mitochondria in dependence on the preparation.

1. The preparation of rat heart mitochondria with Potter-Elvehjem homogenizer results in mitochondria showing stimualtion of respiration induced by Mg2+. This stimualtion is neither caused by adherent hexokinase nor by energy-dependent magnesium accumulation (Mg2+ content in the presence of 10 mM glutamate: 22 nmoles/mg protein; in the presence of glutamate plus antimycin A 21 nmoles/mg protein). 2. The effect of added magnesium is excluded by addition of carboxyatractyloside. This demonstrates the activity of an ATPase outside of the mitochondrial inner membrane. 3. A simple and rapid method for the preparation of Mg2+-insensitive rat heart mitochondria is presented. The minced heart is pressed through a normal syringe and then treated with trypsin. 4. A comparison of mitochondria of both preparations shows that there is no difference in magnesium content and no energy-dependent magnesium influx.

Adenylate Kinase↗
PubMed1978

Mathematical model of regulation of oxidative phosphorylation in intact mitochondria.

1. A mathematical model of the regulation of mitochondrial ATP synthesis by the extramitochondrial ATP/ADP ratio is presented taking into account the transport processes of phosphate and of adenine nucleotides by their specific translocators. 2. In agreement with known experimental data the model describes the control of respiration by the extramitochondrial ATP/ADP ratio as well as the distribution of adenine nucleotides and of inorganic phosphate between the extramitochondrial and the intramitochondrial compartment. 3. In the extramitochondrial compartment the phosphorylation potential is predicted by the model to be higher than in the matrix space. 4. Despite the differences in the phosphorylation potentials no particular translocation energy is necessary. This has been achieved by postulating a charge compensation between the movement of adenine nucleotides and the uptake of phosphate during ATP synthesis. 5. The proton stoichiometry of the proton pump must be higher than stated by the chemiosmotic coupling hypothesis in its present form, otherwise sufficient results could not be obtained. 6. With increasing activities of non-phosphorylating energy requiring side reactions (as uncoupling) at first the difference of the respiration rates between the phosphorylating and the non-phosphorylating state disappears, at higher activities the ADP phosphorylation stops, but the membrane potential collapses at very high activities only.

Adenosine Diphosphate↗
PubMed1978

The dependence on the extramitochondrial ATP/ADP-ratio of the oxidative phosphorylation in mitochondria isolated by a new procedure from rat skeletal muscle.

A simple method for preparation of rat skeletal muscle mitochondria is presented using gentle mechanical homogenization in a syringe and nagarse treatment (EC 3.4.4.16). This method enables the preparation of skeletal muscle mitochondria, whose outer membrane is intact to 95%. Furthermore, with mitochondria prepared by this method the regulation of respiration and phosphorylation by the extramitochondrial ATP/ADP-ratio can be demonstrated. In accordance to rat liver and heart mitochondria and to mitochondria of rabbit reticulocytes, the regulation by the extramitochondrial ATP/ADP-ratio lies in the range from 5 (corresponding to 98% of the maximum respiration) to 100 (corresponding to state 4). At extramitochondrial ATP/ADP-ratios from 0.01 to 1 the respiration rate is nearly constant (maximum rate of respiration).

Adenosine Diphosphate↗
PubMed1976

Control of oxidative phosphorylation by the extra-mitochondrial ATP/ADP ratio.

The control of mitochondrial ATP synthesis by the extramitochondrial adenine nucleotide pattern was investigated with rat liver mitochondria. It is demonstrated that any stationary state between the two limit states of maximum activity (state 3) and of resting activity (state 4) can be obtained by a hexokinase-glucose trap as an ADP-regenerating system. These intermediate states are characterized by stationary respiratory rates, stationary redox levels of the cytochromes b and c and stationary levels of extramitochondrial ATP and ADP between the rates and levels of the limit states. At a constant concentration of inorganic phosphate the activity of mitochondria between the limit states is controlled by the extramitochondrial ATP/ADP ratio independent of the total concentration of adenine nucleotides present. The control range was found to be between ratios of about 5 and 100 at 10 mM phosphate. At lower ratios the mitochondria are in their maximum phosphorylating state. With succinate+rotenone and glutamate+malate the same control range was observed, indicating that it is independent of the nature of substrate oxidized. The results suggest that in the control range the mitochondrial activity is limited by the competition of ADP and ATP for the adenine nucleotide translocator.

Adenosine Diphosphate↗
PubMed1976

The inhibition of isocitrate oxidation by palmitoyl-l-carnitine and palmitoyl-C0 A in rat liver mitochondria.

Palmitoyl-L carnitine decreases the oxidation of isocitrate in rat liver mitochondria in state 3 by 25-30%. Palmitoyl-L-carnitine acts as an additional substrate raising the rate of oxidative phosphorylation, NAD reduction and ATP/ADP ratio in mitochondria. Palmitoyl-CoA added to mitochondria oxidizing isocitrate in state 3 causes a strong inhibition of isocitrate oxidation and of oxidative phosphorylation and a considerable elevation of intramitochondrial NADH/NAD and ATP/ADP ratios. The effect of palmitoyl-CoA is dependent on its concentration and is competitive with ADP. Carnitine restores only oxidative phosphorylation, but the oxidation of isocitrate remains inhibited. Evidence is presented that the transport of isocitrate is not affected by palmitoyl-CoA is due to the inhibition of adenine nucleotide translocation. The kinetic studies of NAD-dependent isocitrate dehydrogenase in the soluble fraction of sonicated mitochondria revealed that the enzyme is very sensitive towards the inhibition by NADH and only very slightly affected by ATP (Ki for NADH and ATP are 0.017 and 3.6 mM respectively). On the basis of the kinetic data the relative contribution of NADH and ATP in the inhibition of isocitrate oxidation by fatty acids was calculated. It is concluded that the inhibition of isocitrate oxidation caused by palmitoyl-L-carnitine and palmitoyl-CoA is primarily due to the increased reduction of NAD, whereas the increase of ATP/ADP ratio is much less important.

Adenosine Diphosphate↗
PubMed1976

Ribosomal DNA content and bobbed phenotype in Drosophila hydei.

The number of ribosomal RNA genes in different Drosophila hydei stocks has been determined by filter saturation hybridisation experiments. It has been shown that there is no marked correlation between the average rRNA gene number per cell in the whole animal and the bobbed phenotype when Y chromosomal nucleolar organisers are present.

Animals↗
PubMed1976

Variations in the number of the Y chromosomal rRNA genes in Drosophila hydei.

The number of rRNA cistrons is measured by filter saturation hybridization in different stocks of D. hydei, where the wild-type X chromosome has one nucleolus organizer (NO) and wild-type Y has two separated NO's. XX/Y females having no X chromosomal NO show an rDNA content exceeding that of a Y chromosome. An even greater increase in the rRNA cistron number is measured in two translocation stocks where the XX is combined with one half of a Y and, therefore, each stock contains only one of the two Y chromosomal NO's. But when the same Y fragments are brought together with a wild-type X chromosome they lose about one-half of their rRNA cistrons within one generation. Males with two complementary Y fragments but having no X chromosomal NO show a considerably higher rDNA content than the XX/Y females, although both are equal in respect of their NO number. Consideration is given to related phenomena in Drosophila melanogaster.

Aneuploidy↗
PubMed1975

Independent replication of the ribosomal RNA genes in the polytrophic-meroistic ovaries of Calliphora erythrocephala, Drosophila hydei, and Sarcophaga barbata.

By filter saturation hybridizations the ribosomal (r)DNA contents of the ovaries Calliphora erythrocephala, Drosophila hydei, and Sarcophaga barbata have been measured in comparison to the rDNA percentages of their diploid brains. The measurements of the ovarian rDNA have been carried out on ovaries where the nurse cells in the distal egg chamber of the ovarioles had reached their highest ploidy level. The diploid rDNA content of each of the respective species was chosen as a 100% standard and the rDNA amounts of the ovaries were related to this 100% level. The results show that the ovaries of C. erythrocephala contain 135% rDNA whereas the rDNA contents in the ovaries of D. hydei and S. barbata are only 51% and 47%, respectively. Measurements carried out on isolated nuclei of the nurse cells and follicle cells in D. hydei show that both have a reduced rDNA content in comparison to the brains (45% and 70%, respectively). The data are discussed in relation to the problem of an rDNA amplification in the germ cells and an rDNA underreplication in polyploid nuclei.

Animals↗