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1.
Frank M. Sulzman Leland N. Edmunds Jr. 《Biochimica et Biophysica Acta (BBA)/General Subjects》1973,320(3)
Possible factors that could generate the circadian oscillations in alanine dehydrogenase (EC 1.4.1.1.) activity observed in cultures of non-dividing Euglena gracilis (Z) have been examined in an effort to learn more about the basic timekeeping mechanism of biological clocks. No differences in Km, pH optimum or electrophoretic mobility could be demonstrated between enzyme extracted from the minimum part of the 24-h oscillation in activity and that extracted from the maximum part. Also, no evidence for the presence of activators or inhibitors was found in mixing experiments. The effect of cycloheximide on the rhythm was examined; it was shown that the oscillation ceases in the presence of the inhibitor, but that if the inhibitor is removed after 12 h, the rhythm resumes with no apparent change in phase. Analyses of gel scans of enzyme preparations partially purified by (NH4)2SO4 fractionation and polyacrylamide gel electrophoresis indicated that there was more alanine dehydrogenase protein present at the maximum part of the cycle than there was at the minimum part. In view of these and other data, an operational model of a circadian biological clock is discussed. 相似文献
2.
Na+ and K+ binding by glycerinated muscle fibers with reciprocal cation concentrations in the medium
The binding of Na+ and K+ by glycerinated muscle fibres was observed at reserve concentrations of NaCl in the medium. Under external concentrations of Na+ of K+ up to 0.4-0.5 mM, a constant fraction (0.15-0.25 mmoles/kg dry weight of the fibres) bound by glycerinated fibres was revealed. With the increase of NaCl or KCl concentration in the medium up to 10 mM the concentration of bound cations increased too. The parameters of Na+ and K+ sorption by glycerinated models were calculated. The values of Na+ and K+ binding limits were 4.4 and 1.8 mmole/kg dry weight of the fibres and those of affinity, 3.2 and 4.1 kcal/mol, respectively. The binding of one cation took place in conditions when its concentration was 10,000-20,000 fold less than that of the other cation. This points to the fact that Na+ and K+ binding is highly specific and is carried out by different centres. It is suggested that myosin ATPase is a substratum binding Na+ and K+ in glycerinated muscle fibres at reverse ratio concentrations of these cations in the medium. 相似文献
3.
J A Shapiro 《Journal of bacteriology》1985,164(3):1171-1181
Pseudomonas putida colonies were examined by scanning electron microscope. A variety of cell morphologies, multicellular arrangements, and extracellular materials were observed in the fixed material. Different regions of a single colony showed characteristic organizations of these architectural elements. In some cases, the detailed microstructure of the fixed colony surfaces observed by scanning electron microscopy could be correlated with macroscopic patterns visualized by histochemical staining and surface relief photography of live colonies. Extracellular materials were seen to extend onto the agar surface beyond the boundaries of the cell mass, and the final structures of these materials, after fixation and desiccation, were colony specific. The significance of these features of colony microstructure for formulating hypotheses about the control of colony morphogenesis is discussed. 相似文献
4.
Hydrobiologia - The taxonomic composition and biomass of phytoplankton in the San Joaquin River, California, were examined in relation to water depth, flow regime, and water chemistry. Without... 相似文献
5.
Trichome-borne and artificially applied acylsugars of wild tomato deter feeding and oviposition of the leafminer Liriomyza trifolii 总被引:1,自引:0,他引:1
D. J. Hawthorne J. A. Shapiro W. M. Tingey M. A. Mutschler 《Entomologia Experimentalis et Applicata》1992,65(1):65-73
Oviposition and adult feeding of the leafminer Liriomyza trifollii (Burgess) (Diptera, Agromyzidae) on Lycopersicon pennellii (Corr.) D'Arcy and its F1 hybrid with Lycopersicon esculentum (Mill.) was significantly less than that on the cultivated tomato, L. esculentum. The resistance of L. pennellii and the F1 was reduced following rinsing of foliage with ethanol. Resistant attributes of L. pennellii were transferred to L. esculentum through appression of L. pennellii foliage to L. esculentum leaflets. Application of purified 2,3,4-tri-O-acylglucoses (the principal component of type IV glandular trichome exudate of L. pennellii) to L. esculentum significantly decreased feeding and oviposition on L. esculentum leaflets by 61–99%. Therefore the principal mechanism of resistance to this leafminer by L. pennellii is the secretion of these acylglucoses. Dose response analysis of acylglucoses applied to L. esculentum shows that dosages as low as 10% those found on L. pennellii provide large reductions (91%) in leaf punctures and mines. 相似文献
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The placental transport and palatal localization of l-thyroxine-125I was studied in Sprague-Dawley rat embryos ages 13 and 14 days in vivo and 14–16 days in vitro. Amniotic fluid, placenta and (by late day 14) embryonic/palatal and liver areas were assayed by scintillation counting and protein analysis. Radioactivity was found in amniotic fluid as early as 13 days in vivo. A small but consistent amount of radioactivity above control levels was found in the embryonic palatal and liver areas. Autoradiographs of thin-layer chromatographs showed that most of the radioactive label was at the thyroxine area in both 13- and 14-day in vivo and 15-day in vitro amniotic fluid pools. A small amount of radioactivity was present in the diiodothyronine area in both. Some activity was also present in the triiodothyronine area in the 13- and 14-day samples. No labelled inorganic iodide was detectable. The thyroid gland in rat does not begin to function until 17 days in utero. Accordingly, the labelled thyroxine was exogenous. The presence of labelling in the embryonic palate suggests a possible involvement of this hormone in palatal embryogenesis. 相似文献
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