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Ia M Koen

Publications and source records attributed to Ia M Koen.

13 recordsLinked to original sources
PubMed1987

[Effect of modifiers of the cytochrome P-450-dependent enzyme system of the liver on the metabolic pathways of diethylnitrosamine activation and inactivation].

Pretreatment of Wistar male rats with antioxidants prevented the toxic effect of diethylnitrosamine (DENA) at LD50. Six-fold acceleration of DENA excretion and significant increase of maximum plasma concentration of a DENA metabolite nitrite were, also observed after antioxidants treatment. Liver microsomal metabolism of DNA was altered by pretreatment with another antioxidant--butylhydroxytoluene, which stimulated selectively denitrosation and inhibited dealkylation of DENA in the microsomal cytochrome P-450-dependent enzyme system. Moreover, butylhydroxytoluene treatment diminished he ability of microsomes to activate DENA to mutagenic intermediates identified in Ames' test. It was suggested that the protective effect of antioxidants against DENA toxicity may be due to the acceleration of its metabolic inactivation and the inhibition of its activation in liver cytochrome P-450-dependent systems.

Animals↗
PubMed1979

[Effect of heparin, spermidine and Be2+ ions on the phosphatase and RNAse activity of rat liver cell nuclei].

Effects of heparin, spermidine, and Be2+ ions on the ATPase and beta-glycerophosphatase and RNA-ase activities of the rat liver cell nuclei were studied. Be2+ was shown to inhibit the ATPase activity and, to a lesser extent, beta-glycerophosphatase activities. Physiological concentrations of heparin and spermidine also lowered the mentioned two activities, as well as the RNAase activity of the nuclei. Evidence is presented for the inhibitory effect of heparin and spermidine on endonucleases.

Adenosine Triphosphatases↗
PubMed1978

[RNA transport from rat liver cell nuclei in vitro. Release of rapidly labeled RNA from isolated nuclei in a cell-free system in the presence of RNAse affectors].

A cell-free system was developed and characterized, which supported RNA release from isolated rat liver cell nuclei. The RNA release in the system seemed to be dependent on the presence of ATP as an evergy source and of dialized cytosol as far as on the temperature level in the incubation mixture. In vitro effects of a number of RNase affectors from cytoplasm and of related exogenous compounds on the RNA release were studied. It was shown that RNase inhibitors such as heparin, PVS and rat liver cytoplasmic RNA were capable to stimulate the RNA release, while the natural inhibitor from liver cytosol failed to influence the RNA relase. Spermidine and PCMB lowered the rate of RNA release from nuclei. The results are discussed in connection with possible role of nuclear RNases and cytoplasmic factors in nucleocytoplasmic transport of RNA.

Adenosine Triphosphate↗
PubMed1978

[Transport of RNA from rat liver cell nuclei in vitro. Effect of superoxide dismutase on the release of rapidly labeled RNA from isolated nuclei].

Purified superoxide dismutase from beaf and rat liver cytosol was found to inhibit in vitro a release of the newly synthesized poly(A)-containing RNA from isolated hepatocyte nuclei in a cell-free system. The inhibition was concentration-dependent. Similar effect was observed with Cu2+ and coppertyrosine complex, which possess SOD-like type catalytic activity. The effectiveness of the complex and of Cu2+ however was an order smaller than that of SOD. The inhibitory effects of SOD and the two other copper-containing compounds could be abolished by potassium cyanide and reduced glutathione as far as by gomologous cytosol. Catalase failed to effect the RNA release. Although serum albumin itself did not affect release of RNA it was capable to abolish the inhibitory effects of Cu2+ and of copper-tyrosine, but not that of SOD. Possible mechanisms for the inhibitory effect of SOD on RNA transfer across the nuclear envelope are discussed.

Animals↗
PubMed1976

[Phospholipid composition of nuclear membranes and cell nuclei of rat liver and hepatoma 27].

Phospholipid composition of nuclei and nuclear membranes from rat liver and hepatoma-27 were investigated. Hepatoma nuclei and nuclear membranes were found to contain cardiolipin which was absent in the same fractions of rat liver. In the nuclei and nuclear membranes of hepatoma the content of sphingomyelin was higher and that of lecithin is lower than in the corresponding subcellular fractions of rat liver. The content of acid phospholipids was much higher in hepatoma nuclear membranes than those of the normal liver. The data obtained show that the general trend of lipid dedifferentiation which earlier was demonstrated for various membranes of different tumor cells is observed also in the case of nuclear membranes.

Animals↗
PubMed1976

[Various enzymes of isolated nuclear membranes and cell nuclei of the liver and hepatoma 27 of rats].

A comparative study of glucose-6-phosphatase, alcaline RNase, ATPase, inosine diphosphatase and 5'-nucleotidase activities in isolated rat liver and hepatoma-27 nuclei and nuclear envelopes was performed. The tumor nuclear membranes were shown to be free from G-6-Pase activity in contrast to the liver nuclear membranes. The nuclear RNase activity was strongly inhibited in the hepatoma and could be unmasked in the presence of 3-10(-4) M pCMB. Hepatoma nuclear and nuclear envelopes ATP-ase activity was found to be moderately decreased as compared to those of the normal tissue. The values of inosine diphosphatase activity in hepatoma were similar to those in liver. The role of the nuclear envelope in nuclear-cytoplasmic interactions as well as nuclear location of G-6-Pase are discussed.

Adenosine Triphosphatases↗
PubMedDate not supplied

[The role of secondary metabolism in formation of benz(a)pyrene dihydrodiol profile in microsome membranes].

4,5-, 7,8- and 9,10-dihydrodiols of benz(a)pyrene (BP) were separated by thin-layer chromatography and their influence on BP-hydroxylase activity was studied in liver microsomes isolated from rats treated with phenobarbital (PB-microsomes) and 3-methylcholanthrene (MC-microsomes). All diols studied inhibited hydroxylation of BP by the competitive type. Accumulation of BP-diols in the incubation media correlated with their affinity to cytochrome P-450 isoenzymes which catalyzed the secondary metabolism of these diols. This correspondence allowed to formulate the kinetic and temperature dependence of BP oxidation suggesting that two main groups of hemoprotein isoforms were contained which were dissimilar in the active site orientation. Treatment with 3-methylcholanthrene induced specifically those hemoproteins which had the active site directed inside the membrane lipids; treatment with phenobarbital involved induction of two groups of hemoproteins active site of which was directed both to lipid and to water. The primary metabolism of the hydrophobic BP involved cytochrome P-450 isoenzymes which had the active site directed inside the lipids; the secondary metabolism of more polar diols was realized using both groups of hemoprotein isoenzymes with active sites oriented into lipids and water.

Animals↗