Adaptation of intestinal amino acid transport

Zusammenfassung An evertierten Dünndarmsäcken (proximales Jejunum) erwachsener Ratten, die zwei Wochen lang eine proteinarme (13% Kasein) oder proteinreiche (88% Kasein) Diät erhalten hatten, wurde der aktive intestinale Transport vonl-Leuzin undd-Galaktose untersucht. Proteinreiche Ernährung führte zu einer Stimulierung desl-Leuzin-Transports, während derd-Galaktose-Transport dadurch unbeeinflusst blieb. Diese Befunde sprechen für eine spezifische Adaptation des intestinalen Aminosäurentransports an den Proteingehalt der Nahrung.     

Serum-induced stimulation of snRNA synthesis in mouse 3T3 fibroblasts

Summary Small nuclear RNAs (snRNAs) from quiescent and serum-stimulated 3T3 cultures, labeled with [³H]uridine ([³H]U), were electrophoresed in polyacrylamide-urea slab gels and revealed by staining with ethidium bromide and by fluorography, Judged by labeling with [³H]U, synthesis of 7S and U1-U6 RNAs was very low or absent in quiescent cultures. The serum-induced transition of 3T3 cells from a resting to a growing state was accompanied by an early, apparently sequential stimulation of snRNA synthesis; stimulated synthesis of 7S, U1, U2, U3, U4 and U6 RNAs coincided in time with serum-induced stimulation of 45S pre-ribosomal RNA (pre-rRNA) and heterogeneous nuclear RNA (hnRNA) synthesis.     

Serum-induced stimulation of snRNA synthesis in mouse 3T3 fibroblasts

Small nuclear RNAs (snRNAs) from quiescent and serum-stimulated 3T3 cultures, labeled with [3H]uridine [( 3H]U), were electrophoresed in polyacrylamide-urea slab gels and revealed by staining with ethidium bromide and by fluorography. Judged by labeling with [3H]U, synthesis of 7S and U1-U6 RNAs was very low or absent in quiescent cultures. The serum-induced transition of 3T3 cells from a resting to a growing state was accompanied by an early, apparently sequential stimulation of snRNA synthesis; stimulated synthesis of 7S, U1, U2, U3, U4 and U6 RNAs coincided in time with serum-induced stimulation of 45S pre-ribosomal RNA (pre-rRNA) and heterogeneous nuclear RNA (hnRNA) synthesis.     

Diethylpyrocarbonate interferes with lipid-protein interaction and glucose transport in the human red cell membrane

Summary Diethylpyrocarbonate largely diminishes both discontinuities in red cell glucose transport and also in red cell membrane ANS fluorescence at about 17–20°C.We are very much indebted to Dr K.-H. Röhm for valuable discussions of this paper. This work was supported by the Deutsche Forschungsgemeinschaft.     

Diethylpyrocarbonate interferes with lipid-protein interaction and glucose transport in the human red cell membrane.

Diethylpyrocarbonate largely diminished both discontinuities in red cell glucose transport and also in red cell membrane ANS fluorescence at about 17--20 degrees C.     

Effect of insulin upon renal amino acid transport in lambs

Zusammenfassung An Nierenrindenschnitten von Lämmern und Schafen wurde untersucht, ob die Anwesenheit von Insulin bzw. Glukagon im Inkubationsmedium die gegen ein Konzentrationsgefälle erfolgende Aufnahme von -Aminoisobuttersäure in Nierenrindenzellen beeinflusst. Insulin stimulierte in diesen Versuchen (Inkubationszeit: 80 min) die Akkumulation von -Aminoisobuttersäure in Nierenrindenzellen bei jungen Lämmern, nicht jedoch bei älteren Lämmern und Schafen. Für Glukagon konnte kein Effekt nachgewiesen werden.

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Acknowledgment. The investigation was supported by the Deutsche Forschungsgemeinschaft (SFB 147 Jungtierkunde).     

Ammonia and amino acid transport across symbiotic membranes in nitrogen-fixing legume nodules

Biological nitrogen fixation involves the reduction of atmospheric N₂ to ammonia by the bacterial enzyme nitrogenase. In legume-rhizobium symbioses, the nitrogenase-producing bacteria (bacteroids) are contained in the infected cells of root nodules within which they are enclosed by a plant membrane to form a structure known as the symbiosome. The plant provides reduced carbon to the bacteroids in exchange for fixed nitrogen, which is exported to the rest of the plant. This exchange is controlled by plant-synthesised transport proteins on the symbiosome membranes. This review summarises our current understanding of these transport processes, focusing on ammonia and amino acid transport. Received 5 June 2000; revised 13 July 2000; accepted 14 July 2000     

Effects of acetaldehyde and/or ethanol on neutral amino acid transport systems in microvillous brush border membrane vesicles prepared from human placenta

Summary At 20 mM of acetaldehyde, the activities of three transport systems of L-alanine distinguished by the difference in their cation dependence, namely 1) Na⁺-specific, 2) Li⁺-dependent, and 3) Na⁺-independent systems, were significantly reduced in a similar manner. Only the Li⁺-dependent system was selectively inhibited at toxic concentrations of acetaldehyde and ethanol.     

Effect of a growth-promoting factor on protein synthesis and amino acid transport in vitro

Zusammenfassung Es wird nachgewiesen, dass sich in der Muskulatur ein Faktor befindet, der eine Anreicherung der -Amino-isobuttersäure in den Zellen hervorruft und der auch in vitro den Einbau von Leucin und damit die Proteinsynthese fördern kann. Ob dieser Faktor als Übermittler für Wachstumshormon wirkt, ist noch nicht abgeklärt.     

Effect of ethanol on amino acid penetration in to mouse brain]

The uptake of large neutral aminoacids across the blood brain of mouse is increased by previously intraperitonealy given ethanol. The uptake of small neutral, acid and basic aminoacids is not modified. Observed increase is correlated with octanol-water istribution coefficient.     

Influence of the transport of amino acids on glucose and sodium transport across the small intestine of the albino rat incubatedin vitro

Riassunto Proseguendo precedenti ricerche si mette in evidenza che esiste una correlazione anche tra trasporto di sodio e trasporto di vari amino acidi attraverso l'intestino tenue isolato di ratto albino. Se ne deduce che presumibilmente ogni sostanza capace di essere trasportata attivamente stimola il trasporto di sodio e che quest'ultima funzione diventa solo un indice dell'attività totale di trasporto dell'epitelio intestinale.

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This work has been supported by a research grant of the Consiglio Nazionale delle Ricerche, Roma.     

Kinetic analysis and simulation of glucose transport in plasma membrane vesicles of glucose-repressed and derepressed Saccharomyces cerevisiae cells

In this study experimental data on the kinetic parameters investigated by other authors 1-5, 11 together with own data on plasma membrane vesicles, have been subjected to a computer simulation based on the equations describing facilitated diffusion. The simulation led to an ideal fit describing the above data. From this it can be concluded that glucose is transported by facilitated diffusion, and not by active transport as was postulated by Van Steveninck 14,15. The simulation method also demonstrates that the fast sampling technique used by these authors 1-5, 11 underestimated the fluxes. Thus, the parameters given do not contribute to the understand of glucose transport under different metabolic conditions. The K value of plasma membrane vesicles prepared from glucose-repressed cells is around 7 mM. Derepression, particularly by galactose, causes a highly significant increase in affinity as shown by a decrease in the K value to 2 mM. The highest affinity was measured in a triple kinaseless mutant grown on glycerol with a K value of 1 mM. It seems, therefore, that the kinetic parameters derived from initial uptake rates of glucose in intact cells 1-5, 11 using single flux analysis, such as Eadie-Hofstee- or Lineweaver-Burk-plots, are in error.     

Possible involvement of protein kinase C in the stimulation of amino acid transport by phorbol ester,platelet-derived growth factor and A23187 in Swiss 3T3 cells

Summary Stimulation of amino acid transport induced by phorbol-12, 13-dibutyrate, platelet-derived growth factor or A23187 was not observed in cells lacking protein kinase C. On the other hand, stimulation of transport by epidermal growth factor or insulin was not affected. These results suggested that the stimulation of amino acid transport is mediated by at least two separate pathways.This work was supported in part by Grants-in-Aid for Scientific Research from the Ministry of Education, Science and Culture, and the Ministry of Health and Welfare of Japan.