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1. (1) Evidence is presented which indicates that the carbocyanine dye (3,3′ dipropyl thiadicarbocyanine) can be used as a spectroscopic probe for monitoring the resting potential across the plasma membrane of the ciliated protozoan Paramecium.
2. (2) The dye at low concentrations ( 1 μM) does not affect either the viability or the motility of the cells, nor does it induce a chemotactic response.
3. (3) The fluorescence of the dye bound to the cells alters as the potential across the membrane is changed by increasing the external cation concentration.
4. (4) The absorbance of the bound dye also changes in response to an alteration of the membrane potential.
5. (5) The membrane potential changes as measured by the fluorescence method have been correlated with the measurements of the potential estimated by microelectrode methods.
6. (6) Both cations which induce a negative chemotactic response in Paramecium (K+, Na+, Ba2+) and several non-toxic cations bring about a rapid depolarization of the plasma membrane. The significance of these rapid changes in relation to the swimming behaviour of the ciliate is discussed.
Abbreviations: diSC3(5); 3; 3′-dipropylthiadicarbocyanine  相似文献   

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Injection of 3,5,3′ l-triiodothyronine (15 μg/100 g) induces a biphasic enhancement of rat heart ornithine decarboxylase (EC. 4.1.17) activity after 4 and 21 hours. This induction is observed after each daily injection, but to a lesser extent.The properties of partially purified basal enzyme and induced enzyme, at 21h, after single injections have been compared.
1) Affinity for ornithine is the same for both enzymes, but affinity for pyridoxal-phosphate is 40-fold higher for the induced one.
2) Thermostability studies suggest that basal and induced enzymes have different conformations.
3) The two enzymes have similar immunoreactivity.
4) The comparisons of the time-dependent activity curve after injection and of the antigen/activity ratio suggests that triiodothyronine induces the synthesis of new molecules of enzymes and that an inhibition of the enzyme activity also occurs which explains the biphasic induction.

Résumé

L'injection de 3,5,3′ l-triiodothyronine (15 μg/100 g) induit une augmentation biphasique de l'activité ornithine décarboxylase (EC: 4.1.1.17) de cœur de rat à la 4e et 21e heure. Ce phénomène se reproduit après chaque injection quotidienne, mais de manière moins intense.Les enzymes, basale et induite à la 21e heure après une injection de T3, ont été partiellement purifiées et leurs propriétés comparées:
1) L'affinité des deux enzymes pour l'ornithine est identique, mais l'affinité pour le pyridoxal-phosphate est 40 fois plus élevée pour l'enzyme induite.
2) Les études de thermodénaturation suggèrent que les enzymes de base et induite présentent des conformations différentes.
3) Les deux enzymes présentent des immunoréactivités similaires.
4) Une comparaison de la courbe d'activité et du rapport antigène/activité enzymatique au cours du temps, après induction suggèrent que la triiodothyronine induit la synthèse de novo de l'enzyme, mais qu'intervient également un phénomène d'inhibition qui explique l'aspect biphasique de l'induction.
Mots-clés: régulation; ornithine décarboxylase; triiodothyronine; antizymeKeywords: regulation; ornithine decarboxylase; triiodothyronine; antizyme  相似文献   

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1. 1. Cu2+ at a concentration of 10−4 M, when applied to the external side of the frog skin produces an increase in the short-circuit current (Isc).
2. 2. This effect was studied in skins of Rana temporaria adapted to cold (5°C) and room temperature (20°C), skins of Rana pipiens adapted to cold, and the results compared with those obtained previously with Rana ribibunda.
3. 3. The observed effect is less dependent upon the adaptation to cold than upon the functional state of the skin: skins with low short circuit currents have a bigger response to Cu2+ than skins with high Isc.
4. 4. A species difference cannot be ruled out since skins of Rana ribibunda exhibiting high Isc give good responses to Cu2+.
5. 5. 5,5′-dithiobis(2-nitrobenzoic acid), a sulphydryl-oxidizing reagent, produces an effect similar to that of Cu2+, and dithiothreitol an SH-reducing agent, reverses the effect of this ion.
6. 6. Cu2+ also induces an increase in the unidirectional K+ fluxes and unmasks a net outward potassium flux.
7. 7. The outward K+ flux induced by Cu2+ is sensitive to ouabain.
8. 8. It is concluded that Cu2+ increases the permeability of the external barrier of the frog skin to Na+ and K+, probably by reacting with SH groups.
Abbreviations: DTNB; 5; 5′-dithiobis(2-nitrobenzoic acid)  相似文献   

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1. 1. Particulate fractions of costal cartilage from young rats are capable of catalyzing the formation of the first two monosaccharide units of the chondroitin sulfate-protein linkage region.
2. 2. Hormonal imbalance has been shown to influence the activity of the glycosyltransferases responsible for the sequential transfer of xylose and galactose from UDPxylose and UDPgalactose, respectively, in the formation of the linkage region.
3. 3. The activity of xylosyltransferase was found to be decreased in costal cartilage of diabetic, thyroidectomized and hypophysectomized rats, but not in rats injected with either testosterone or hydrocortisone. In the latter two treatment groups, galactosyltransferase activity was decreased only in the group receiving hydrocorsitone.
4. 4. The combined results of this and previous studies suggest that decreased levels of chondroitin sulfate in diabetic, thyroidectomized and hypophysectomized animals are due to interference in the synthesis of the linkage region of the proteoglycan at the xylosyltransferase level whereas hydrocortisone acts primarily at the level of the galactosyltransferase.
Abbreviations: P-ado-P-S; 3′-phosphoadenosine-5′-phosphosulphate  相似文献   

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K W Bock  R Weiner  J Schultz 《Enzyme》1976,21(6):488-494
In the isolated perfused rat liver, both 5-aminolevulinate synthetase and tyrosine aminotransferase were induced by the addition of 3.5 mmol/l allylisopropylacetamide and 58 mumol/l dexamethasone to the perfusion medium. Glucose (40 mmol/l) did not affect either the induction of these enzymes or the intrahepatic level of cyclic AMP. The results suggest that the glucose effect on the induction of 5-aminolevulinate synthetase and tyrosine aminotransferase in vivo is mediated by extrahepatic factors.  相似文献   

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