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71.
72.
Insulin and adrenaline were both found to stimulate the glucose utilization of Tetrahymena, although somewhat differently. With exogenous sugar added, adrenaline always drops the glucose level in all regions of the unicellular, while the effect of insulin was less unequivocal. 相似文献
73.
- 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
74.
Summary The regulation of the synthesis of nucleoside metabolizing enzymes has been studied in cya and crp mutant strains of Escherichia coli.The synthesis of the cyt-enzymes, cytidine deaminase and uridine phosphorylase regulated by the cytR gene product, is activated by the cAMP-CRP complex. On the other hand the synthesis of the deoenzymes: deoxyriboaldolase, thymidine phosphorylase, phosphodeoxyribomutase and purine nucleoside phosphorylase, appears to be increased if an active cAMP-CRP complex cannot be formed.It also seems that nucleosides serve as poor carbon sources for cya and crp mutants; this could not solely be explained by low levels of nucleoside metabolizing enzymes nor by a deficiency in nucleoside uptake. Addition of casamino acids stimulated the growth of cya and crp mutants, with nucleosides as carbon sources. When grown on glucose and casamino acids growth could be stimulated by adenine and hypoxanthine nucleosides; these results suggest an impaired nitrogen metabolism in cya and crp mutants.Abbreviations and Symbols cAMP
cyclic adenosine 3:5-monophosphate
- CRP
cAMP receptor protein. Genes coding for: adenyl cyclase
-
cya
cAMP receptor protein
-
crp
cytidine deaminase
-
cdd
uridine phosphorylase
-
udp
thymidine phosphorylase
-
tpp
purine nucleoside phosphorylase
-
pup; cytR
regulatory gene for cdd, udp, dra, tpp, drm, and pup
-
deoR
regulatory gene for dra, tpp, drm, and pup 相似文献
75.
76.
J Rehacek M Zupancicová E Kovácová J Urv?lgyi R Brezina 《Journal of hygiene, epidemiology, microbiology, and immunology》1976,21(3):306-313
Experimental studies of infection of Apodemus flavicollis, and for comparison of rickettsiaemia in Clethrionomys glareolus and of susceptibility and antibody formation in white mice, with rickettsiae of the SF group isolated in Slovakia, gave the following results: the species A. flavicollis reacted by the formation of antibodies on subcutaneous administration of rickettsiae, strain B, in an amount of 10(0.5) EID 50/0.25 ml, whereas the white mouse only in an amount of 10(2.5). Rickettsiae, strain B, administered in an amount of 10(3.5) EID 50/0.25 ml subcutaneously to A. flavicollis were found in smears from the liver and spleen of the inoculated animals up to the 25th day following infection, on detection by the isolation test on chick embryo yolk sacs in the spleen on day 5 and 7, in lymph nodes on day 7 and in the brain on day 15 following infection; on detection by the method of injecting suspension from the organs into the haemocoelom of ticks regularly in the spleen and liver up to the 10th day, in the brain, kidney and lymph nodes regularly up to the 15th and irregularly in the lungs also up to the 15th day, then regularly in the testes up to the 5th day and in the heart, blood and peritoneum up to the 3rd day after infection. 相似文献
77.
Studying the brain circuits that control behavior is challenging, since in addition to their structural complexity there are continuous feedback interactions between actions and sensed inputs from the environment. It is therefore important to identify mathematical principles that can be used to develop testable hypotheses. In this study, we use ideas and concepts from systems biology to study the dopamine system, which controls learning, motivation, and movement. Using data from neuronal recordings in behavioral experiments, we developed a mathematical model for dopamine responses and the effect of dopamine on movement. We show that the dopamine system shares core functional analogies with bacterial chemotaxis. Just as chemotaxis robustly climbs chemical attractant gradients, the dopamine circuit performs ‘reward-taxis’ where the attractant is the expected value of reward. The reward-taxis mechanism provides a simple explanation for scale-invariant dopaminergic responses and for matching in free operant settings, and makes testable quantitative predictions. We propose that reward-taxis is a simple and robust navigation strategy that complements other, more goal-directed navigation mechanisms. 相似文献
78.
Evidence for Geographic Isolation and Signs of Endemism within a Protistan Morphospecies 总被引:4,自引:0,他引:4 下载免费PDF全文
Jens Boenigk Karin Pfandl Tobias Garstecki Hauke Harms Gianfranco Novarino Antonis Chatzinotas 《Applied microbiology》2006,72(8):5159-5164
The possible existence of endemism among microorganisms resulting from and preserved by geographic isolation is one of the most controversial topics in microbial ecology. We isolated 31 strains of “Spumella-like” flagellates from remote sampling sites from all continents, including Antarctica. These and another 23 isolates from a former study were characterized morphologically and by small-subunit rRNA gene sequence analysis and tested for the maximum temperature tolerance. Only a minority of the Spumella morpho- and phylotypes from the geographically isolated Antarctic continent follow the worldwide trend of a linear correlation between ambient (air) temperature during strain isolation and heat tolerance of the isolates. A high percentage of the Antarctic isolates, but none of the isolates from locations on all other continents, were obligate psychrophilic, although some of the latter were isolated at low ambient temperatures. The drastic deviation of Antarctic representatives of Spumella from the global trend of temperature adaptation of this morphospecies provides strong evidence for geographic transport restriction of a microorganism; i.e., Antarctic protistan communities are less influenced by transport of protists to and from the Antarctic continent than by local adaptation, a subtle form of endemism. 相似文献
79.
Biofilm formation and dispersal in Gram-positive bacteria 总被引:1,自引:0,他引:1
Biofilms are structured communities of bacteria, which are adhered to a surface and embedded in a self-produced matrix of extracellular polymeric substances. Since biofilms are very resistant to antimicrobial agents, they are at the basis of a range of problems, including quality and safety issues in food industry. Recently, major advances have been made in elucidating the different structural components of the biofilm matrix, the regulatory pathways involved in biofilm formation, and signaling molecules involved in biofilm formation and dispersal, which provide opportunities for prevention and control of these biofilms in the food industry. 相似文献
80.