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41.
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Ricardo Pablo Garay 《生物化学与生物物理学报:生物膜》1982,688(3):786-792
Human erythrocytes are able to incorporate cyclic AMP (cAMP) in amounts larger than those required to saturate cAMP-dependent protein kinase. In contrast to previous observations in avian red blood cells in which cAMP stimulates the Na+/K+ cotransport system, we demonstrate that cAMP inhibits this system in human erythrocytes. The cotransport inhibition is enhanced by addition of phosphodiesterase inhibitor 1-methyl-3-isobutylxanthine to the incubation medium. The cAMP concentration giving half-maximal cotransport inhibition showed a wide variation among different individuals (from 0.1 to 5 mM external cAMP concentration). In contrast to cAMP, cyclic GMP showed little effect on the cotransport system. Ca2+ introduced into the cell interior was an inhibitor of the Na+/K+ cotransport system. These results suggest that in human cells in which endogeneous levels of cAMP and Ca2+ are modulated by hormones, the Na+/K+ cotransport system may be under hormonal regulation. 相似文献
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Pablo Collazo Lluís Montoliu Pere Puigdomènech Joan Rigau 《Plant molecular biology》1992,20(5):857-867
The isolation and characterization of cDNA and homologous genomic clones encoding the lignin O-methyltransferase (OMT) from maize is reported. The cDNA clone has been isolated by differential screening of maize root cDNA library. Southern analysis indicates that a single gene codes for this protein. The genomic sequence contains a single 916 bp intron. The deduced protein sequence from DNA shares significant homology with the recently reported lignin-bispecific caffeic acid/5-hydroxyferulic OMTs from alfalfa and aspen. It also shares homology with OMTs from bovine pineal glands and a purple non-sulfur photosynthetic bacterium. The mRNA of this gene is present at different levels in distinct organs of the plant with the highest accumulation detected in the elongation zone of roots. Bacterial extracts from clones containing the maize OMT cDNA show an activity in methylation of caffeic acid to ferulic acid comparable to that existing in the plant extracts. These results indicate that the described gene encodes the caffeic acid 3-O-methyltransferase (COMT) involved in the lignin biosynthesis of maize. 相似文献
45.
A R Mattiazzi H E Cingolani 《Archives internationales de physiologie et de biochimie》1981,89(2):167-174
The effects of papaverine and isoproterenol on the isometric twitch and high KCl-induced contractures were compared in papillary muscles from reserpinized cats. Papaverine (10(-5) M) significantly increased developed tension (T), maximal rate of rise of tension (+dT/dt max) and maximal velocity of relaxation (--dT/dt max) in 52.3 +/- 6.1, 74.1 +/- 6.7 and 82.1 +/- 12.1% respectively with respect to control values. Time to peak tension (TTP) and contracture tension decreased in 9.1 +/- 2.0% and 50.9 +/- 5.6% respectively with respect to controls (P less than 0.05). Isoproterenol in a dose (8 X 10(-10) M), that produced an increase in +dT/dt max non significantly different to the one elicited by papaverine (65.6 +/- 9.0%), increased (in % with respect to control values), T in 55.3 +/- 7.3, --dT/mx in 73.8 +/- 13.1 and decreased TTP in 6.6 +/- 1.1 and contracture tension in 40.7 +/- 6.3 (P less than 0.05). The effects of isoproterenol on all the parameters studied were not statistically different from the ones of papaverine. It is concluded that in cat papillary muscles, papaverine has a positive inotropic action and an isoproterenol-like relaxant effect. 相似文献
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David S. Auld Ikuo Atsuya Carmen Campino Pablo Valenzuela 《Biochemical and biophysical research communications》1976,69(2):548-554
Microwave excitation spectrometry and metal binding inhibition studies show that zinc is a catlytically essential component of the highly purified RNA polymerase I from yeast, the first eukaryotic RNA polymerase I available in quantities sufficient for such studies. It contains 2.4 g-atom of zinc based on a molecular weight of 6.5 × 105 (8). Copper, iron, manganese and magnesium are absent, i.e., below the limits of detection, 10?13 to 10?14 g-atoms. A number of derivatives of 1,10-phenanthroline reversibly inhibit the polymerase catalyzed reaction, apparently by forming a ternary polymerase·Zn·OP complex while the nonchelating isomer, 1,7-phenanthroline, is ineffective. 相似文献
49.
Patterns of variation in desiccation resistance in a set of recombinant inbred lines in Drosophila melanogaster 下载免费PDF全文
Federico H. Gomez Pablo D. Sambucetti Volker Loeschcke Fabian M. Norry 《Physiological Entomology》2015,40(3):205-211
Desiccation, resulting from extremely dry environmental conditions, is a serious obstacle to the survival of organisms. Water is vital for the maintenance of intracellular structure and prevents the irreversible formation of aggregates, an occurrence leading to loss of cellular function. To characterize genetic variation in desiccation stress resistance (DSR) in Drosophila melanogaster Meigen, an intercontinental set of recombinant inbred lines (RIL) is used. Flies are exposed to a low humidity environment (<10% relative humidity) at a constant temperature of 25 °C. Desiccation stress resistance is higher in RIL derived from a backcross to the parental stock sensitive to heat stress (from Denmark) than in RIL derived from the reciprocal backcross to the heat‐stress resistant stock (from Australia). Composite interval mapping reveals significant quantitative trail loci (QTL) for DSR in the set of RIL. Both major and minor effects QTL are detected, suggesting a complex genetic architecture. When compared with a previous investigation performed on the same set of RIL, the present study indicates that not all traits of resistance to environmental stressors are affected in the same direction by segregating co‐localized QTL. 相似文献
50.
James M. Bullock Stephen J. Galsworthy Pablo Manzano Peter Poschlod Carsten Eichberg Katherine Walker Matthias C. Wichmann 《Oikos》2011,120(8):1201-1208
Studies of external seed transport on animals usually assume that the probability of detachment is constant, so that seed retention should show a simple exponential relationship with time. This assumption has not been tested explicitly, and may lead to inaccurate representation of long distance seed dispersal by animals. We test the assumption by comparing the fit to empirical data of simple, two‐parameter functions. Fifty‐two data sets were obtained from five published studies, describing seed retention of 32 plant species on sheep, cattle, deer, goats and mice. Model selection suggested a simple exponential function was adequate for data sets in which seed retention was followed for short periods ( <48 h). The data gathered over longer periods (49–219 days) were best described by the power exponential function, a form of the stretched exponential which allows a changing dropping rate. In these cases the power exponential showed that seed dropping rate decreased with time, suggesting that seeds vary in attachment, with some seeds becoming deeply buried or wound up in the animal's coat. Comparison of fitted parameters across all the data sets also confirmed that seeds with adhesive structures have lower dropping rates than those without. We conclude that the seed dropping rate often changes with time during external transport on animals and that the power exponential is an effective function to describe this change. We advise that, to analyse seed dropping rates adequately, retention should be measured over reasonable time periods – until most seeds are dropped – and both the simple and power exponential functions should be fitted to the resulting data. To increase its utility, we provide functions describing the seed dropping rate and the dispersal kernel resulting from the power exponential relationship. 相似文献