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W Siems

Publications and source records attributed to W Siems.

At least 73 records · Page 4Linked to original sources
PubMed1989

Balancing of mitochondrial and glycolytic ATP production and of the ATP-consuming processes of Ehrlich mouse ascites tumour cells in a high phosphate medium.

A balance of energy budgeting of Ehrlich mouse ascites tumour cells including mitochondrial and glycolytic ATP production and about 80% of ATP consumption in a high phosphate medium is presented. In the share of glycolysis was about one-third of the total ATP production, more than twice that found in a low phosphate medium. The extent of a single energy reaction was assessed from the decrease of coupled oxygen consumption and lactate formation following the specific inhibition of this process. The inhibitory effects on coupled respiration and glycolysis were identical for the energy consuming processes measured: protein turnover, Na+/K(+)-ATPase, Ca2(+)-transport and RNA synthesis.

Adenosine Triphosphate↗
PubMed1989

Nucleotide degradation and radical formation in ischemic and reperfused small intestine.

Peroxidative loading during the reoxygenation of the rat small intestine following a complete ischemia was demonstrated in in vivo-experiments by the increases of the glutathione disulphide (GSSG): total glutathione ratio and the concentration of thiobarbituric acid-reactive substances (TBA-RS). The pretreatment of the rats with allopurinol diminished the accumulation of GSSG and of TBA-RS. From these effects was concluded that the purine nucleotide degradation is an important source of oxygen reduction products leading to peroxidations. The concentrations of nucleotides, nucleosides and nucleobases were measured by an ion-pair reversed-phase HPLC. The restoration of ATP and GTP concentrations during the reoxygenation period was accelerated by the application of allopurinol.

Adenine Nucleotides↗
PubMed1989

Nucleotide concentrations in hepatocytes during anoxia and reoxygenation in presence of allopurinol and oxypurinol.

In hepatocytes of starved rats nucleotide, nucleoside and nucleobase concentrations were measured during and following anoxia. A complete restoration of ATP is observed during reoxygenation after anoxic periods less than 60 minutes. GTP cannot be completely restored after 30 minutes of anoxia. Allopurinol and oxypurinol do not accelerate the ATP and GTP restoration. IMP, adenosine and AMP concentrations are increased in presence of allopurinol or oxypurinol during anoxia and reoxygenation.

Adenosine Triphosphate↗
PubMed1989

Changes in the nucleotide metabolism of Ehrlich ascites tumour cells during their growth in vivo.

During the transition of Ehrlich mouse ascites tumour cells from the proliferating into the resting phase of growth a tremendous loss of purine and pyrimidine compounds was quantitated by ion-pair reversed-phase high performance liquid chromatography. This change is accompanied by a distinct decline in the incorporation rates of adenine, hypoxanthine, and adenosine. Inorganic phosphate stimulates the low rate of hypoxanthine incorporation of cells in the plateau phase, but lacks any effect on the high rate during proliferation. The mitochondria suffer structural deteriorations and decrease in their cellular content in the course of the plateau phase; however, other changes were not seen by morphometric analysis. The interrelations between nucleotide metabolism, mitochondrial content and the rates of formation and consumption of ATP are discussed.

Adenine↗
PubMed1988

Purine and pyridine nucleotides in rabbit red blood cells of different maturity.

Using reversed-phase high-performance liquid chromatography purine nucleotides, nucleosides and nucleobases as well as pyridine nucleotides were determined in extracts of reticulocytes and mature red blood cells of rabbits. The concentrations of almost all compounds measured decrease during the last phase of red blood cell maturation. These changes were interpreted with respect to the loss of mitochondria, accompanied by shifting the energy production from the preferentially oxidative mode to the exclusively glycolytic one and variations in the concentrations of purine compounds in blood plasma during reticulocytosis.

Adenine Nucleotides↗
PubMed1987

Determination of nucleotides, nucleosides and nucleobases in cells of different complexity by reversed-phase and ion-pair high-performance liquid chromatography.

Procedures are presented for the analysis of profiles of purine and pyridine compounds in human and rabbit red blood cells by reversed-phase high-performance liquid chromatography and in Ehrlich ascites tumour cells of mouse by ion-pair high-performance liquid chromatography. These compounds are present in rabbit erythrocytes in higher concentrations than in human blood cells, and in rabbit reticulocytes the concentration of purine compounds is still higher. During glucose-free incubation, human red cells accumulate adenosine and adenine in the presence of coformycin owing to the inhibition of adenosine and AMP deamination. Ehrlich ascites tumour cells lose major portions of purine mono-, di- and triphosphates between the seventh and eleventh day after inoculation into mouse peritoneal cavities.

Animals↗
PubMed1987

Hydroxylation of fatty acids and alcohols by hepatic microsomal cytochrome P-450 system from the Mongolian gerbil.

The liver microsomes of the Mongolian gerbil Meriones unguiculatus catalyzed the hydroxylation of various saturated fatty acids (C8-c18), alcohols (C12 and C16) and hydrocarbon (C12) to the corresponding omega- and (omega-1)-hydroxy derivatives. Lauric acid was hydroxylated most effectively among saturated fatty acids and the order of activity as hydroxylation substrates was C12 greater than C14 greater than C13 greater than C16 greater than C10 greater than C18 greater than C8. The specific activity of laurate hydroxylation (5.99 nmol/mg microsomal protein/min) in gerbil liver microsomes was higher than that observed in other species. 1-Dodecanol was also hydroxylated very effectively (4.58 nmol/mg microsomal protein/min) by gerbil liver microsomes, but in general the hydroxylation rates for fatty alcohols were much lower than those for the corresponding acids. It was found from both inhibitor and cofactor studies that the enzyme catalyzing the hydroxylation of fatty acids and alcohols in the liver microsomes of the Mongolian gerbil was a typical cytochrome P-450-linked monooxygenase, and at least two different cytochrome P-450 species were involved in the hydroxylation.

Animals↗
PubMed1987

Damage of erythrocytes by activated oxygen generated in hypoxic rat liver.

The implication of activated oxygen in the interaction between hypoxic rat liver and circulating erythrocytes was investigated. Reduced species of oxygen generated in hypoxic liver owing to accelerated purine nucleotide degradation via xanthine oxidase initiate alterations of plasma membrane and glutathione system of erythrocytes. Osmotic fragility, hemolysis rate and erythrocytic GSSG:GSH ratio may be considered as appropriate indicators of oxidative load in liver and other tissues. Addition of erythrocytes to the perfusion medium attenuates the GSSG efflux of hypoxic liver from 2.7 +/- 0.5 nmol x g w.w.-1 x min-1 to 1.4 +/- 0.2 nmol x g w.w.-1 x min-1 Thus, circulating erythrocytes protect the liver against oxidative attack.

Animals↗
PubMed1986

Quantification of ATP-producing and consuming processes of Ehrlich ascites tumour cells.

ATP production of Ehrlich ascites tumour cells was estimated on the basis of their coupled respiration and lactate formation. ATP-consuming processes were assessed from the effects of selective inhibitors of RNA synthesis, protein synthesis and proteolysis, Na+/K+-ATPase on respiration. The extent of protein synthesis and proteolysis were also determined directly. From these values and those of the inhibition of respiration by selective inhibitors, a P/O ratio of 2.2 was calculated. About 75% of the total ATP consumption could be assigned to specific processes. The major ATP-consuming processes of tumour cells in an amino-acid-enriched medium, in which they are in an approximate steady state, are protein synthesis with about 30% of total ATP consumption, and Na+/K+-ATPase with about 20%, while RNA synthesis, ATP-dependent proteolysis and Ca2+-ATPase contribute about 10% each. In an amino-acid-free glucose medium, protein synthesis is reduced to a third, with a corresponding decrease of respiration, whereas the rate of the other ATP-consuming processes is unchanged.

Adenosine Triphosphatases↗
PubMed1986

H2O2 formation during nucleotide degradation in the hypoxic rat liver: a quantitative approach.

In the hypoxic liver an increased rate of cytosolic and peroxisomal H2O2 generation is due to the accelerated purine nucleotide degradation. The relative contribution of the oxidase type of xanthine oxidoreductase activity increases in hypoxia by less than 10%, the dehydrogenase type of this enzyme is hardly inhibited by the increased concentration of free NADH. Nevertheless, due to the high hypoxanthine supply the xanthine oxidase related H2O2 formation is increased six-fold and together with the peroxisomal uricase-mediated share it accounts for half of the oxygen consumption.

Animals↗
PubMed1986

ATP production and consumption of rabbit reticulocytes increase in an amino-acid-enriched medium.

The ATP production and the main processes of ATP consumption, globin synthesis, Na+, K+-ATPase, and proteolysis of rabbit reticulocytes in two different media (1. complete medium with amino acids and glucose and 2. glucose containing electrolyte medium) were measured. The ATP formation in the complete medium amounts to 157 mmol/l X h which is 28% higher than in the incomplete medium. The increased ATP formation rate is due to increased ATP consumption by the more than doubled protein synthesis in the complete medium, whereas proteolysis and Na+,K+-ATPase are nearly unchanged. The increase in the glucose consumption in the complete medium is not fully accounted for by the increased oxidative degradation of glucose in the citric acid cycle and by lactate accumulation.

Adenosine Triphosphate↗
PubMed1985

Formation of activated oxygen in the hypoxic rat liver.

The biliary GSSG efflux rate of normoxic perfused rat liver was 1.5 +/- 0.2 nmol/min/g liver wet weight. The GSSG efflux rate as indicator for the flux through the glutathione peroxidase reaction and, therefore, for an oxidative loading increased with the extent of hypoxia. 2.6 +/- 0.5 nmol/min/g were released from the severely hypoxic liver. The hydroxyl radical scavenger formate as well as the xanthine oxidase inhibitor allopurinol reduced the efflux rate of GSSG. GSH was released from the perfused liver at a rate of 15.5 nmol/min/g which was nearly unchanged in severe hypoxia. The high rate of glucose liberation from the hypoxic liver declined to almost that of the normoxic organ in the presence of formate. There is an 'oxidative stress' during hypoxic liver perfusion which probably originates from increased generation of activated oxygen species in the degradation of purine nucleotides.

Animals↗
PubMed1984

Accounting for the ATP-consuming processes in rabbit reticulocytes.

The report deals with a detailed balance of ATP production and consumption of the rabbit reticulocyte. The sum-total of ATP produced amounts to 135 mmol . 1-1 . h-1. About 70% of the ATP consumption has been accounted for by specific processes. The main contributing processes are the globin synthesis with about 28%, the Na+, K+-ATPase with 23% and the proteolysis with more than 15%. 30% of ATP consumption has not been accounted for. Cycloheximide (20 microM) leads to a dissociation between synthesis and degradation of proteins, which argues against any obligatory connection between these processes. More than 90% of the lysine liberated from mitochondria by proteolysis were reutilized for the globin synthesis demonstrating the high nitrogen economy of reticulocytes. Each of the ATP-consuming processes studied appears to control ATP production in an independent manner without competition with each other.

Adenosine Triphosphate↗