The discrimination between Rb+ and K+ by Escherichia coli is changed after bacteriophage T7 infection

Rb+ and K+ have similar chemical properties. They share the uptake systems in Escherichia coli and can replace each other inside the cell. These common features led to experiments in which the radioactive isotope 86Rb was used to trace intracellular K+ fluxes. However, the E. coli pumps discriminate between these two ions and one should thus be cautious using 86Rb+ as a tracer for K+. We now report that T7 infection alters the degree of discrimination in such a way that changes of intracellular Rb+ do not reflect changes of K+. It has been observed that shortly after infection the 86Rb+ level was strongly reduced (Ponta, H., Altendorf, K.-H. and Schweiger, M. (1976) Mol. Gen. Genet. 149, 145-150). In contrast, determination of the K+ content showed no change directly after infection (Kuhn, A., Jütte, H. and Kellenberger, E. (1983) J. Virol. 47, 540-552). The efflux of 86Rb was only evident when Rb+ was used in trace amounts. In media conditions under which intracellular K+ was mainly replaced by Rb+, 86Rb+ efflux was not observed.     

INTERRELATIONSHIPS BETWEEN POLYAMINES AND NUCLEIC ACIDS. CHANGES OF POLYAMINE AND NUCLEIC ACID CONCENTRATIONS IN THE GROWING FISH BRAIN (SALMO IRIDEUS GIBB.)

Abstract— In contrast to mouse brain, the content of putrescine in fish brain considerably exceeds that of spermine and spermidine. While we observed constant protein, RNA and spermidine concentrations in fish brains of weights between 60 and 800 mg, DNA and spermine concentrations diminished with increasing brain weight, the content of spermine per cell being constant throughout life. It can be concluded from our results that growth of fish brain results both from cell enlargement and cell proliferation. The concomitant changes of spermine and DNA concentrations in the growing fish brain are the first example of a direct quantitative relationship between these cell constituents and provides evidence on their possible functional relationship in the cell nucleus.     

Putrescine derivatives as substrates of spermidine synthase

1. Derivatives of 1,4-butanediamine (putrescine) were studied in vitro and in vivo as potential substrates of spermidine synthase. 2. Substituents in the 1-position decreased the reaction rate by steric hindrance, and in the case of electron withdrawing groups there was an additional decrease due to the lowered basicity of the vicinal amino group. 3. Substituents in the 2-position are tolerated; under saturating conditions reaction rates are comparable to those of putrescine. 4. Compounds which were identified as substrates of spermidine synthase in vitro formed derivatives of spermidine and spermine in vivo. Exception: compounds, such as 1-methylputrescine formed in vivo only a spermidine derivative, because the second aminopropylation was sterically hindered by the substituent on the carbon atom next to the amino group. 5. Administration of 2-hydroxyputrescine to alpha-difluoromethylornithine-pretreated chick embryos produced spermidine and spermine analogues in amounts exceeding spermidine and spermine formation from putrescine under comparable conditions. 6. Since the concentration of 2-hydroxyputrescine in the embryo was higher than that of putrescine and all other putrescine analogues, it appears that uptake of the polyamine precursor from the yolk may be rate limiting. 7. Three days after administration of 5 mM alpha-difluoromethylornithine there is a near-to-complete arrest of embryonal growth. 8. A series of diamines supported growth under these conditions, even if they were not substrates of spermidine synthase. 9. Survival of chick embryos was, however, only supported if the diamines were capable of forming significant amounts of spermidine and spermine analogues.     

On the subcellular localization of the polyamines

Putrescine, spermidine and spermine were determined in the nuclear fraction of rat liver which was obtained by density gradient centrifugation in non-aqueous media, i.e. under conditions which avoid migration of water-soluble compounds. Calculations of the distribution of the polyamines between nuclear and extranuclear compartments were based on the assumption that the DNA is concentrated in the nuclei. No significant losses of the polyamines occurred during fractionation. From the polyamine determination in tissue and nuclear fraction it appeared that 16-17% of the liver spermidine and spermine, and about 8% of the putrescine content was localized in the nuclei. The spermidine/spermine-ratios in nuclei and whole tissue were not significantly different. Pretreatment of the animals with inhibitors of ornithine decarboxylase caused a decrease of putrescine exclusively in the extranuclear compartments, in agreement with a higher proportion of the inhibitors in the cytoplasm. Since the nuclear volume of rat liver corresponds to about 5% of total liver volume, the concentration of spermidine and spermine is higher in the nucleus than in extranuclear compartments. Published histochemical localizations of the polyamines suggested very low polyamine concentrations in the nuclei of non-dividing liver and HeLa cells, but dramatic polyamine accumulations in metaphase and anaphase nuclei. These results are in disagreement with previously reported autoradiographic data, subcellular localizations based on density gradient centrifugations, and with our present results. Since subcellular localization is a key issue in all attempts to clarify cellular functions of the polyamines the careful revision of the techniques involved in subcellular polyamine localizations seems imperative.     

Activation of rat liver S-adenosylmethionine decarboxylase by putrescine and 2-substituted 1,4-butanediamines

1. The activation of S-adenosyl-L-methionine decarboxylase (SAM-DC) by putrescine and a series of 1,4-butanediamines with a substituent in position 2 was studied. 2. Kinetic data show the activation of SAM-DC by putrescine is essentially uncompetitive. 3. All 2-substituted 1,4-butanediamines were activators, although not as potent as putrescine itself. 4. At high concentrations of SAM activation of SAM-DC by putrescine and putrescine analogs deviated considerably from uncompetitive activation kinetics. 5. In order to explain the experimental data, especially the non-linearity of the "fractional velocity plots", it was necessary to postulate two independent, but equivalent activator binding sites, for which substrate (SAM) and activator compete. 6. Based on this kinetic model an equation was derived which describes the rate of SAM decarboxylation as a function of substrate and activator concentrations. 7. From the simulated curves, approximate values for equilibrium constants for the binding of activator and substrate to the activator binding sites, and relative rate constants for the product forming steps were calculated. 8. Even a minor change of the structure, such as the substitution of one hydrogen atom by fluorine in the 2-position of putrescine had a very considerable effect on the potency of activation. 9. It is apparent that the structural requirements of an activator of SAM-DC are highly specific.     

Specific inhibition of polyamine oxidase in vivo is a method for the elucidation of its physiological role

N1-Methyl-N2-(2,3-butadienyl)-1,4-butanediamine (MDL 72521) and N1,N2-bis(2,3-butadienyl)-1,4-butanediamine (MDL 72527) are specific, potent, enzyme-activated, irreversible inhibitors of polyamine oxidase in vitro. These compounds are also capable of completely inhibiting polyamine oxidase in mouse tissues at intraperitoneal doses greater than 20 mg/kg. Enzyme activity reappears in the various organs within 2-3 days to 50% of the control values. Irreversible inhibition of polyamine oxidase in mice led to decreased putrescine (30-40%) and spermidine (10-20%) levels in liver and some other organs. At the same time N1-acetylspermidine and, to a lesser extent, N1-acetylspermine were accumulating at rates which are assumed to be related to the rates of polyamine degradation. Even after treatment with polyamine oxidase inhibitors over a period of 6 weeks at doses which produced complete inhibition of polyamine oxidase in all organs, including the brain, neither toxic effects nor changes in body weight or behaviour were observed.     

Polyamine reutilization and turnover in brain

N¹, N²-bis-(2, 3-butadienyl)-1, 4-butanediamine (MDL 72527) is an irreversible, specific inhibitor of polyamine oxidase, which allows one to completely inactivate this enzyme in all organs of an experimental animal. As a result one observes a linear increase of N¹-acetylsperimidine and N¹-acetylspermine concentrations in brain. The rate of accumulation seems directly proportional to the rate of spermidine, and spermine degradation respectively, and since no compensatory changes of the polyamine synthetic enzymes, were induced by inhibition of polyamine oxidase, the rate of acetyl-polyamine accumulation is assumed to be a measure for polyamine turnover. The decrease of brain putrescine levels by 70 percent in the brains of MDL 72527-treated animals suggests the quantitative significance of putrescine reutilisation. Pretreatment of the animals with D, L--difluoromethylornithine, an irreversible inhibitor of ornithine decarboxylase reduced both, polyamine turnover rate and the extent of putrescine reutilization. Inhibition of GAPA-T produced a significant increase of polyamine turnover in brain, in agreement with the known induction of ornithine decarboxylase activity after treatment with inhibitors of GABA-T.