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Biomedical subjects

W Kunz

Publications and source records attributed to W Kunz.

At least 109 records · Page 6Linked to original sources
PubMed1981

Relationship between the energy cost of ATP transport and ATP synthesis in mitochondria.

Liver mitochondria form rats kept on a high-protein diet exhibit an increased rate of respiration upon addition of ornithine in the presence of HCO2 and NH+4. This is the manifestation of intramitochondrial utilization of ATP for the synthesis of citrulline. State 3 respiration of these mitochondria could be adjusted to the same rate as that produced by ornithine by either using limiting amounts of hexokinase or titration with atractyloside. Under such conditions, in both systems the proton-motive force, the intramitochondrial ATP/ADP ratio and the redox state of the respiratory chain were the same. In contrast to this, the ATP/O ratio (equal to 2 X citrulline/O ratio) in mitochondria synthesizing citrulline was higher than the glucose 6-phosphate/O ratio in the system where ATP was trapped extramitochondrially. The ratio of these two ratios was close to 1.5 with both glutamate and succinate as respiratory substrates. From these results it can be concluded that the translocation of ATP against ADP and phosphate utilizes an amount of the chemiosmotic proton gradient equal to half of that needed for the synthesis of ATP in the inner compartment.

Adenosine Diphosphate↗
PubMed1981

Polyamine responses in a solid transplanted tumor (S180) in liver and in urine during endotoxin-induced tumor injury in the mouse.

Polyamine (PA) and ATP concentrations have been measured in the S180 sarcoma damaged by endotoxin (1) 4 hours after administration, coinciding with the onset of hemorrhage, (2) at 8 hours, and (3) at 24 hours, preceeding overt necrosis. The putrescine (PU) content increased promptly, the spermidine (SPD) level dropped by 30% between 8 and 24 hours, while the spermine (SPM) concentration remained unchanged. The ATP level fell, reaching 1% of the control value at 24 hours. The parallel between increases in tumor PU content and urinary PU excretion appears to be largely fortuitous; no similar correlations existed in the cases of SPD and SPM. The development of tumor stasis and the alterations seen in PA metabolism of tumor-free controls suggest that the changes in liver PA concentrations and in urinary excretion primarily reflect responses of nonmalignant cells. Both these findings in animals without tumors and existing data from other experimental systems are consistent with the thesis that PA response patterns to a particular procedure are qualitatively similar regardless of the presence or absence of a malignant growth, and are characteristic of the procedure employed.

Adenosine Triphosphate↗
PubMed1981

Intervening sequences in ribosomal RNA genes and bobbed phenotype in Drosophila hydei.

The "bobbed' (bb) mutation in Drosophila is represented phenotypically by shortened and abnormally thin scutellar bristles and by delayed development. There is a direct correlation between bristle size and ribosomal RNA (rRNA) synthesis, and the bb mutation was at first explained as a deficiency of rRNA genes (rDNA). However, the bb phenotype can occur in Drosophila melanogaster and Drosophila hydei with high rDNA content, while phenotypically wild-type flies are known with few rRNA genes, suggesting that what matters is not the number of rRNA genes but their transcriptional activity. In D. melanogaster, it has recently emerged that rRNA genes interrupted by an intervening sequence are not transcribed. We now report that in D. hydei, the length of the scutellar bristle is directly proportional to the number of rRNA genes without this intervening sequence.

Animals↗
PubMed1981

Influence of different energy drains on the interrelationship between the rate of respiration, proton-motive force and adenine nucleotide patterns in isolated mitochondria.

The respiration of rat liver mitochondria was stimulated by three different ways of energy drain: (a) partial uncoupling (equivalent to direct collapse of the proton-motive force), (b) intramitochondrial utilization of ATP for citrulline synthesis, and (c) extramitochondrial utilization of ATP for glucose phosphorylation. At identical rates of respiration, the intramitochondrial ATP : ADP ratios were the same in all three systems. Furthermore, the proton-motive force was the same in partially uncoupled mitochondria and in the presence of hexokinase plus glucose up to a respiration rate amounting to about 60% of that of the fully active state. However, external ATP : ADP ratios were considerably different in various systems at comparable rates of oxygen uptake, being the lowest under conditions when ATP was being utilized externally. On this basis, it is concluded that the respiratory rate is controlled directly by the proton-motive force and the mitochondrial ATP-synthesizing system operates under near-equilibrium conditions with respect to the membrane energy state parameters. However, a disequilibrium exists at the step of the transport of ATP from mitochondria to the external (cytoplasmic) compartment.

Adenosine Diphosphate↗
PubMed1981

Distribution of spacer length classes and the intervening sequence among different nucleolus organizers in Drosophila hydei.

Drosophila hydei rRNA genes from different chromosomes and from different stocks have been studied by restriction enzyme analysis. In DNA from wild-type females, about half of the X chromosomal rRNA genes are interrupted by an intervening sequence within the 28S coding region. In contrast to D. melanogaster, the intervening sequences belong to a single size class of 6.0 kb. Although there are two nucleolus organizers on the Y chromosome, genes containing the intervening sequence seem to be restricted to the X chromosome. -- As shown in four cloned rDNA fragments, the nontranscribed spacers differ in length by having varying numbers of a 242 base pair sequence located in tandem in the right section of the spacer. In genomic rDNA, the spacers also differ in length by a regular 0.25 kb interval. Spacers with between 5 and 15 subrepeats occur frequently within the X and Y chromosomal nucleolus organizers in different D. hydei stocks; shorter and longer spacers are also present but are relatively rare. -- Although each genotype is characterized by different frequencies of some spacer classes, the prominent spacer length heterogeneity pattern is similar among the different nucleolus organizers and, therefore, seems to be conserved during evolution.

Animals↗
PubMed1980

Investigation of the dependence of the intramitochondrial [ATP]/[ADP] ratio on the respiration rate.

The relationship between the respiration rate and the intra- and extramitochondrial adenine nucleotides was investigated in isolated rat liver mitochondria. For the determination of adenine nucleotide patterns in both compartments a new procedure was developed, based on the evaluation of these metabolites from incubation of various amounts of mitochondria under identical stationary states of oxidative phosphorylation. These identical states were adjusted by addition of appropriate amounts of hexokinase to a glucose-containing incubation mixture. Adenine nucleotides were measured in aliquots of the total extract of the incubation mixture without any separation. The concentrations of the adenine nucleotides in both compartments were obtained from a plot of the total concentration of these species versus mitochondrial protein. Disturbances of this method by unspecific efflux of adenine nucleotides could be excluded. The results obtained for the total adenine nucleotide content (12 nmol . mg-1 protein) and the intramitochondrial [ATP]/[ADP] ratio (about 4 in the resting state) are in good agreement with data obtained by other methods. Strong evidence is provided for a decrease in the intramitochondrial [ATP]/[ADP] ratio with increasing rate of oxygen consumption. Therefore it is not necessary to assume a microcompartmentation of the intramitochondrial adenine nucleotide pool in respect to the ATPase reaction and the adenine nucleotide translocation.

Adenosine Diphosphate↗
PubMed1980

Characterization of cloned ribosomal DNA from Drosophila hydei.

The structure of ribosomal genes from the fly Drosophila hydei has been analyzed. EcoRI fragments, cloned in a plasmid vector, were mapped by restriction enzyme analysis. The lengths of the regions coding for 18S and 28S rRNA were defined by R-loop formation. From these data a physical map of the rRNA genes was constructed. There are two major types of rDNA units in D. hydei, one having a size of 11 kb and the other a size of 17 kb. The 17 kb unit results from an intervening sequence (ivs) of 6.0 kb, interrupting the beta-28S rRNA coding region. Some homology between th D. hydei ivs and D. melanogaster type 1 ivs has been described previously (1). However, the restriction sites within these ivs show considerable divergence. Whereas D. hydei rDNA D. melanogaster rDNA, the nontranscribed spacer has little, if any, sequence homology. Despite difference in sequence, D. hydei and D. melanogaster spacers show structural similarities in that both contain repeated sequence elements of similar size and location.

Animals↗
PubMed1980

Disproportionate rDNA replication does occur in diploid tissue in Drosophila hydei.

The rDNA content in Drosophila hydei has been compared in wild-type and in two translocation genotypes possessing only one nucleolus organizer. In highly polyploid salivary glands where rDNA is underreplicated, an 'independent polytenization' of the rDNA occurs resulting in about the same rDNA level in each genotype independently of the number of nucleolous organizers present in the genome. Thus, the situation in the salivary glands of D. hydei is similar to that in D. melanogaster (Spear and Gall 1973). In tetraploid thoracic muscle where rDNA is not underreplicated, the rDNA percentage in the two translocation genotypes is also considerably increased, although the wild-type level is not completely attained. This result shows that rDNA replication is independently controlled even in a non-underreplicating tissue. In larval diploid brain the situation in the two translocation stocks is dissimilar: in one genotype the rDNA content remains unaltered whereas in the other it is increased. This demonstrates for the first time that a gene compensation does occur in a diploid tissue.

Animals↗
PubMed1980

Effect of ethanol on microsomal metabolism of dimethylnitrosamine.

Rat liver microsomes were prepared from male and female controls and from animals pretreated for 3 weeks with ethanol, and incubated with dimethylnitrosamine (DMN) and an NADPH-regenerating system. The formation of formaldehyde and nitrite as well as the alkylation of microsomal protein were found to be greatly enhanced, especially in the low DMN concentration range, as a result of long-term ethanol induction. In contrast, ethanol or tetrahydrofuran, when incubated simultaneously with DMN, inhibited microsomal metabolism of the carcinogen.

Animals↗
PubMed1980

Denitrosation of N-nitrosomorpholine by liver microsomes; possible role of cytochrome P-450.

Liver microsomes from male mice and rats were incubated with N-nitrosomorpholine (MoNA) and an NADPH-regenerating system. The formation of nitrite was measured after induction or inhibition of the microsomal monooxygenase system. Pretreatment of the animals with phenobarbital (PB) enhanced nitrite formation by about 200%, while 3-methylcholanthrene (3-MC)-induction showed no exceptional effects. Various specific inhibitors of the monooxygenase function including carbon monoxide decreased nitrite formation. In conjunction with results obtained by spectra studies it is suggested that N-nitrosomorpholine is denitrosated by a reduction process in which cytochrome (cyt.) P-450 seems to be involved. Nitricoxide formed is partly converted to nitrite under these conditions.

Aminoacetonitrile↗
PubMed1980

The multifunctional actions of beta-thujaplicin on the oxidative energy transformations as a consequence of its lipophilic and chelating properties.

The influence of the fungicidic compound beta-thujaplicin (beta-isopropyl-tropolone) on the energy transformation processes of oxidative phosphorylation was investigated in isolated rat liver mitochondria with succinate (plus rotenone) as substrate. To elucidate the observed strong inhibition of active respiration by beta-thujaplicin three possibilities were assayed: the inhibition of 1) transport processes across the inner mitochondrial membrane for inorganic phosphate, adenine nucleotides, or succinate, 2) electron flux along the respiratory chain, and 3) mitochondrial ATPase. In this respect a remarkable inhibition of both Pi transport and the translocation of adenine nucleotides could not be observed. However, the effective suppression of the DNP-induced ATPase by beta-thujaplicin explains the pronounced inhibition of active respiration. An impairment of succinate transport and the measured partial inhibition of the terminal respiratory chain at the level of cytochrome oxidase contribute to the less marked inhibition of the uncoupled respiration. The ability of beta-thujaplicin to extract mitochondrial Mg++ and the prevention of the effects of beta-thujaplicin by an excess of Mg++ in the medium suggest a common mode of action of beta-thujaplicin as a lipophilic chelator of Mg++ and other divalent cations.

Adenosine Diphosphate↗
PubMed1980

[Relation between intactness and adenine nucleotide pattern of ejaculated bull spermatozoa].

The intactness of bull spermatozoa was determined by exclusion of external succinate. This was oxygraphically measured in the presence of cytochrome c after inhibition of the cell respiration with rotenone. An addition of cytochrome c was necessary for a reproducible respiration of damaged cells. The portion of intact cells determined in this way correlated with that obtained by the fluorescent dye primuline. The content of adenine nucleotides and the percentage of ATP of washed fresh spermatozoa depended on the intactness of the sperm sample. The adenine nucleotide pattern of spermatozoa after deep freezing corresponded to that of washed fresh ejaculates with a high percentage of damaged cells. The major part of ejaculates tested showed only a small increase of damaged cells during substrate-free incubations at 38 degrees C up to 4 h under aerobic and anaerobic conditions. Ejaculates which had shown a drastic increase of damaged cells were not recognizable by the initial portion of damaged cells. Also a lowered content of ATP in the cells was no indicator of an increased fragility of the cell membrane. A remarkable loss of total adenine nucleotides was observed under conditions of cold shock. It indicates that the changes in the sperm membrane induced by cold shock were qualitatively different in comparison with changes caused by storage and by a slow decrease in temperature.

Adenine Nucleotides↗