Early changes in mitochondrial monoamine oxidase activity of rat liver during 2-acetylaminofluorene feeding

The activities of mitochondrial type A and B monoamine oxidase were determined in the liver of rats fed a diet containing 2-acetylaminofluorene (AAF). Three days after the initiation of AAF-feeding, there was a significant decrease of type B monoamine oxidase activity without affect on type A enzyme. The decreased activity of type B monoamine oxidase, which reached a minimum after three weeks, was sustained for as long as AAF-feeding was continued. Sex-related difference in response to AAF was seen in the rat with respect to the onset and the intensity of the decreased type B monoamine oxidase activity, male rats being more sensitive to the carcinogen than female rats. In contrast to the in vivo effect, AAF showed a potent inhibitory effect on type A monoamine oxidase, rather than on type B enzyme, when added in vitro. The pI₅₀ values were estimated to be 7.5 against type A monoamine oxidase and 4.1 against type B enzyme, respectively. The in vitro inhibition of both types of monoamine oxidase by AAF was competitive. The K_i values for AAF were calculated to be 9.51 · 10^?9 M for type A monoamine oxidase and 1.30 · 10^?5 M for type B enzyme, respectively. In accordance with the potent inhibitory effect of AAF on type A monoamine oxidase in vitro, a single administration of the carcinogen, at a dose of 50 mg/kg, resulted in a marked and temporal decrease of the enzyme activity in the mitochondria of male rat liver. Recovery of the decreased type B monoamine oxidase activity was slow, and the enzyme activity did not return to control levels, even if rats were fed the basal diet for 2 or 4 weeks after the cessation of AAF-feeding.     

Feeding preference by the male blowfly Phormia regina for some natural foods and its relation to carbohydrate, amino acid, and alcohol content

The male blowfly, Phormia regina Meigen shows preference among a variety of natural and artificial foods. In a laboratory study preference was observed among sweet and fermenting juices as well as between liver and fish. The preferences between fresh and fermenting juices were based not only on component sugars, but also on other components, namely, amino acids, alcohol salts and presumably other chemical compounds. The preference between decaying liver and fish was probably based partly on the composition and concentration of amino acids in these foods. A variety of amino acids were found in foods and some of these amino acids were shown to be excitatory, some inhibitory and others neutral. Salts were also observed to be present in the juices; and in a laboratory study NaCl at lower concentrations acted synergestically with 0.1 M sucrose and at higher concentrations repulsive. It is suggested that feeding preference is based on several chemicals which behave either in an excitatory, additive, neutral, inhibitory or synergistic manner. The ratio of excitants to inhibitants is important in deciding the direction of preference.

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Résumé P. regina Meigen mâle préfere certains aliments naturels ou artificiels. Au laboratoire ses préférences parmi les jus sucrés sont les suivantes: orange > miel > pomme > sucrose 0.1 M; et parmi les aliments en décomposition: sucrose 0.1 M > foie > poisson. Les jus frais sont préférés aux jus fermentés. Les préférences ne dépendent pas seulement de la nature des sucres, mais aussi des acides aminés, de l'alcool, des sels et probablement d'autres substances chimiques. Le foie contient à la fois le plus grand nombre et la concentration la plus élevée en acides aminés, ce qui explique partiellement le goût pour le foie. Expérimentalement on peut classer les acides aminés en stimulants, inhibiteurs et neutres. Des sels ont été notés dans les jus, mais aucune analyse qualitative et quantitative n'en a été faite. Mélangé à du sucrose à 0.1 M, NaCl agit en synergie aux faibles concentrations, devient neutre à 0.175 M et à des concentrations supérieures le sucrose seul est préféré au mélange avec NaCl. Cependant, un mélange de NaCl à 0.25 M (bien qu'une telle concentration soit peu probable dans des jus végétaux) avec du sucrose à 0.1 M était préféré à l'eau. Il en est déduit que les préférences alimentaires. dans la nature sont orientées par plusieurs substances chimiques qui se comportent d'une façon stimulante, additive, neutre, inhibitrice ou synergique, et que les préférences alimentaires sont relatives. Le rapport de stimulants sur inhibiteurs est important dans la détermination du sens de la préférence.

     

Membrane Binding and Homodimerization of Atg16 Via Two Distinct Protein Regions is Essential for Autophagy in Yeast

Macroautophagy is a bulk degradation mechanism in eukaryotic cells. Efficiency of an essential step of this process in yeast, Atg8 lipidation, relies on the presence of Atg16, a subunit of the Atg12–Atg5-Atg16 complex acting as the E3-like enzyme in the ubiquitination-like reaction. A current view on the functional structure of Atg16 in the yeast S. cerevisiae comes from the two crystal structures that reveal the Atg5-interacting α-helix linked via a flexible linker to another α-helix of Atg16, which then assembles into a homodimer. This view does not explain the results of previous in vitro studies revealing Atg16-dependent deformations of membranes and liposome-binding of the Atg12–Atg5 conjugate upon addition of Atg16. Here we show that Atg16 acts as both a homodimerizing and peripheral membrane-binding polypeptide. These two characteristics are imposed by the two distinct regions that are disordered in the nascent protein. Atg16 binds to membranes in vivo via the amphipathic α-helix (amino acid residues 113–131) that has a coiled-coil-like propensity and a strong hydrophobic face for insertion into the membrane. The other protein region (residues 64–99) possesses a coiled-coil propensity, but not amphipathicity, and is dispensable for membrane anchoring of Atg16. This region acts as a Leu-zipper essential for formation of the Atg16 homodimer. Mutagenic disruption in either of these two distinct domains renders Atg16 proteins that, in contrast to wild type, completely fail to rescue the autophagy-defective phenotype of atg16Δ cells. Together, the results of this study yield a model for the molecular mechanism of Atg16 function in macroautophagy.     

Study on the enzymatic 5′-deiodination of 3′,5′-diiodothyronine using a radioimmunoassay for 3′-iodothyronine

A radioimmunoassay for 3′-iodothyronine has been developed. All iodothyronine analogues (except 3,3′-diiodothyronine) showed very little (0.02% at most) cross-reactivity, and the assay was sensitive to 1 pg 3′-iodothyronine/ tube. We have studied the 5′-deiodination of 3′,5′-diiodothyronine by rat liver microsomal fraction in the presence of dithiothreitol. Production of 3′-iodothyronine at 37°C was found to be linear with time of incubation up to 30 min and with concentration of microsomal protein up to 100 μg/ml. The reaction rate reached a limit on increasing 3′,5′-diiodothyronine concentration to 10 μM. The effect of pH on 3′-iodothyronine production was found to depend on 3′,5′-diiodothyronine concentration. Increasing 3′,5′-diiodothyronine concentration from 0.1 to 10 μM resulted in a shift of the pH optimum from 6–6.5 to 7.5. Similar effects on the 5′-deiodination of 3,3′,5′-triiodothyronine were observed, supporting the hypothesis that these reactions are catalysed by a single enzyme (iodothyronine 5′-deiodinase).     

Arginase,an s-phase enzyme in a human cell line

Suspension cultures of ‘Chang liver’ cells were synchronized by preincubation in a glutamine-deficient medium or by thymidine blockade. Specific arginase activity varied in the synchronized cultures, being high when the number of S-phase cells was maximal. A relationship between high arginase activity and a high percentage of (S+G₂) cells was also found when unsynchronized cells were separated by velocity sedimentation. The increase in arginase activity near the G₁/S border was totally inhibited in the presence of cycloheximide. The rate of decrease in activity after addition of the drug indicated that the variations in the rate of synthesis of the enzyme, while the rate of degradation was more or less constant, corresponding to 4–6% per h. The role of arginase in cells lacking a urea cycle and the regulation of arginase activity in ‘Chang liver’ cells is discussed.     

Growth of ectomycorrhizal fungi stimulated by lipids from a pine root exudate

Summary The content of fatty acids was analysed in an exudate from roots of pine seedlings grown axenically in vermiculite with a synthetic nutrient medium. The dominating fatty acdis were fewer in the exudate than in the roots. Unsaturated fatty acids were predominant. The total lipid fraction of the exudate promoted mycelial growth in two of the three ectomycorrhizal fungi tested.     

Liver fatty acid-binding protein in two cases of human lipid storage

Summary FABPs in the various tissues play an important role in the intracellular fatty acid transport and metabolism. Reye's syndrome (RS) and multisystemic lipid storage (MLS) are human disorders characterized by a disturbance of lipid metabolism of unknown etiology. We investigated for the first time L-FABP in these two conditions. Affinity purified antibodies against chicken L-FABP were raised in rabbits, and found to cross-react specifically with partially purified human L-FABP. L-FABP content in liver samples of two patients with RS and MLS was investigated by immuno-histochemistry, SDS-PAGE and ELISA. L-FABP immuno-histochemistry showed increased reactivity in the liver of RS patient and normal reactivity in MLS liver. L-FABP increase in RS liver was confirmed by densitometry of SDS-PAGE and ELISA method. By these two methods the increase amounted to 180% and 199% (p < 0.02), respectively, as compared to controls. A possible role of L-FABP in the pathogenesis of RS is discussed.