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51.
The high-affinity uptake system of phosphatelimited cyanobacterium Anacystis nidulans [Synechococcus leopoliensis (Raciborski) Komarek] is characterized by a threshold value below which uptake cannot occur. Here it is shown that, if phosphate-limited cyanobacteria are challenged with a short pulse of high phosphate concentration that appreciably exceeds this threshold value, the uptake system undergoes an adaptive response, leading to the attainment of new kinetic properties and a new threshold value. These new properties are maintained for several hours after the pulse. A notable characteristic of this new state is a wide linear dependence of the uptake rate on the external phosphate potential that is a function of the driving force of the uptake process. According to theoretical arguments it is shown that this “linear operation mode” can be explained by the simultaneous operation of several uptake systems with different, staggered threshold values and kinetic properties. Moreover, the new linear uptake properties, in turn, reflect the prehistory of phosphate supply experienced by the population. The consequences of this result with regard to environmental fluctuations of the phosphate concentration in lakes are discussed. 相似文献
52.
53.
S. A. Smith T. Caceci † H. E-S. Marei ‡ H. A. El-Habback § 《Journal of fish biology》1995,46(2):241-254
In the angelfish ( Pterophyllum scalare scalare ) numerous rodlet cells were found in the large post-orbital blood vessel caudal to the eye and in the surrounding extravascular space. Within the vessel the rodlet cells formed striking regular arrays, along the inner aspect of the wall. The rodlets within the cells were positive to PAS but negative to Sudan Black B, Masson's, and the Fuelgen stain. The capsule around the cells was negative for all these stains. These rodlet cells appeared to be traversing the vessel endothelium, and to be pushing the endothelium aside without damaging it. Some discharged their contents into the vessel, but we never observed the release of intact rodlets. The nuclei of rodlet cells in actual contact with the vessel were at the end of the cell more distant from the endothelial wall. Cell-to-cell adhesion structures or communications junctions between rodlet cells and the endothelium were not evident. A putative rodlet cell precursor in the extravascular space contained large electron-dense granules, and extended pseudopodia that contacted nearby rodlet cells. Based on their morphology, tissue distribution, and their behaviour, we conclude that the rodlet cell is an endogeneous teleost cell type, and possibly represents a form of matured granulocyte. 相似文献
54.
Evidence for Glutamatergic Projections from the Cochlear Nucleus to the Superior Olive and the Ventral Nucleus of the Lateral Lemniscus 总被引:2,自引:0,他引:2
Abstract: This study attempts to determine if projections ascending from the guinea pig cochlear nucleus (CN) could be glutamatergic and/or aspartatergic. Multiple radio frequency lesions were made to ablate the right CN. The ablation was verified histologically. To identify the principal targets of CN efferents, silver impregnation methods were used to localize the preterminal degeneration of fibers in transverse sections of the brainstem 5 and 7 days after CN ablation. CN efferents projected heavily to the lateral superior olive (LSO) ipsilaterally, the medial superior olive (MSO) bilaterally, and contralaterally to the medial (MNTB) and ventral (VNTB) nuclei of the trapezoid body, the ventral (VNLL) and intermediate nuclei of the lateral lemniscus and the central nucleus of the inferior colliculus (ICc). There were smaller projections to the lateral nucleus of the trapezoid body ipsilaterally, the dorsal and dorsomedial periolivary nuclei bilaterally, and the dorsal nucleus of the lateral lemniscus contralaterally. There were sparse projections to the VNLL and ICc ipsilaterally and the CN contralaterally, and a very sparse projection to the contralateral LSO. To determine if CN efferents were glutamatergic and/or aspartatergic, the fresh brainstem was sectioned transversely and samples of the LSO, MSO, MNTB, VNLL, and ICc were taken to measure the electrically evoked release and the uptake of d -[3H]Asp and [14C]Gly or [14C]GABA 3–5 days after the CN ablation. The release studies suggest that only certain of the histologically identified projections ascending from the CN may be glutamatergic and/or aspartatergic. CN ablation depressed d -[3H]Asp release in the MSO bilaterally and in the contralateral MNTB and VNLL, suggesting that the CN efferents to these nuclei may use glutamate or aspartate as a transmitter. It was unclear whether a marginal depression of d -[3H]Asp release in the ipsilateral LSO reflected the presence of glutamatergic CN projections to this nucleus. d -[3H]Asp release in the ICc was unaffected, suggesting that CN efferents to this nucleus may not be glutamatergic. There were no deficits in d -[3H]Asp uptake. [14C]Gly release from the LSO and MSO was unchanged. [14C]Gly uptake was unchanged in the MSO and depressed only in the contralateral LSO, possibly reflecting subnormal uptake activity in endings contributed by contralateral MNTB cells that had lost their CN efferents. [14C]GABA uptake in the MNTB, VNLL, and ICc was unchanged. [14C]GABA release was unchanged in the VNLL and ICc. [14C]GABA release was depressed only in the contralateral MNTB, possibly reflecting the loss of a small complement of GABAergic CN efferents and the reaction of GABAergic projections from the contralateral VNTB to their loss of CN efferents. 相似文献
55.
56.
Ahmed Chadli Jean-Pierre LeCaer Dominique Bladier Raymonde Joubert-Caron Michel Caron 《Journal of neurochemistry》1997,68(4):1640-1647
Abstract: Our previous studies have characterized an endogenous lectin from human brain identified as galectin-1. A soluble ligand of galectin-1 was purified from human brain by affinity chromatography and preparative electrophoresis. The purified ligand (termed HBGp82, for human brain galectin-1-binding polypeptide of 82,000 daltons) has an apparent molecular mass of 82 kDa and is glycosylated by N -linked biantennary complex structures. HBGp82 was partially characterized by microsequencing of peptide fragments. Similar peptides were found in a heat shock of protein of 90,000 daltons, hsp90. However, comparison of apparent molecular weights and matrix-assisted laser desorption mass spectrometry clearly showed that HBGp82 differs to some degree from hsp90. 相似文献
57.
58.
DNA fingerprinting of tadpoles from two different ‘one female-two male’ matings of the red-eyed treefrog, Agalychnis callidryas, revealed multiple paternity of offspring. Offspring were assigned paternity based on bands shared with the putative father, but not shared between putative fathers or with the mother. Paternity was split 44/56% and 36/64% in two matings. These results do not support a hypothesis of sperm priority in access to unfertilized eggs by primary males. Multiple paternity may be commonplace in species of anurans with matings by multiple males. 相似文献
59.
R. Godbout B. L. Gallie R. A. Phillips 《In vitro cellular & developmental biology. Plant》1984,20(6):479-485
Summary A variant nontransformed clone, I21, was selected from the spontaneously transformed mouse fibroblast line, IT22. Selection
was done by plating IT22 in methylcellulose and picking single cells after 2 d. Cultures derived from these single cells were
selected again and one clone, I21, derived from the second round of selection was characterized extensively. I21 and IT22
have the same plating efficiency (PE) on plastic, but in agarose they differ by 1000-fold. In comparison to IT22, I21 has
a normal morphological appearance, a lower saturation density, a higher viability in stationary phase, an increased doubling
time, an increased chromosome content, and is unable to form tumors in nude mice. I21 has remained remarkably stable in culture
and has not reverted to the transformed phenotype for at least 300 generations in culture. Over 100 clones of I21, expanded
to 106 cells, failed to show an increased PE in agarose. Even expansion of the rare colonies of I21 that grow in agarose failed
to produce clones similar to IT22.
The research was supported by the Medical Research Council and the National Cancer Institute of Canada. R. Godbout was supported
by a 1967 Science Scholarship and by an MRC Studentship. B. L. Gallie is a Research Associate of the Ontario Cancer Treatment
and Research Foundation. 相似文献
60.
Four c-type cytochromes were purified by several procedures including chromatography on DEAE-Sepharose CL-6B, Phenyl-Sepharose CL-4B and Sephadex G-75, G-100 and G-200 and chromatofocusing. Cytochrome c-551 had a pI value of 5.2 and an Mr of 260 000 consisting of six non-covalently bound polypeptides each with an Mr of 43 000, and contained four to five haems. Cytochrome c-552.5 had a pI value of 4.8 and an Mr of 56 000 consisting of two polypeptides with the same Mr 29 000, and contained two haems. Cytochromes c-551 and c-552.5 were reduced by ascorbate to about 70 and 60% of the fully dithionite-reduced values, respectively, and both were essential components in the thiosulphate-oxidizing multi-enzyme system (other components of the system were ‘enzyme A’, ‘enzyme B’ and sulphite: cytochrome c oxidoreductase). These two cytochromes functioned as electron carriers and effectors in the oxidation of thiosulphate. Some evidence suggested that cytochrome c-551 might be a specialized electron transfer component for sulphonate-sulphur oxidation. Both cytochromes could be reduced by thiosulphate in the presence of enzymes A and B. Cytochrome c-550 (basic) and cytochrome c-550 (acidic) were small proteins with Mr 15 000 and 14 000 and pI values of over 8 and 5, respectively. Their physiological role is uncertain. 相似文献