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121.
The relative contents of chondroitin 4- and 6-sulfates in cartilages of different human bones are reported. Articular and vertebral body cartilages contain almost exclusively chondroitin 6-sulfate, whereas growth and subarticular cartilages contain nearly equal amounts of chondroitin 4-sulfate and chondroitin 6-sulfate. Adult cartilages, where the calcification process is complete, contain only chondroitin 6-sulfate. These results that chondroitin 4-sulfate may be an important component for the calcification process, whereas chondroitin 6-sulfate seems to be related to the integrity of the articular surfaces. A chemical defect of chondroitin 6-sulfate in a new mucopolysaccharidosis, characterized by platyspondyly and irregularities of articular surfaces, is in agreement with these results. 相似文献
122.
The ability of growing mycoplasma cells and their isolated membranes to take up exogenous phospholipids was correlated with their ability to take up cholesterol. Horse serum or vesicles made of phosphatidylcholine and cholesterol served as lipid donors. Growing cells of five Mycoplasma species took up significant quantities of phosphatidylcholine and sphingomyelin as well as free and esterified cholesterol. In contrast, growing cells of three Acholeplasma species failed to take up any of the exogenous phospholipids, and only incorporated low amounts of free cholesterol and no esterified cholesterol. Hence, the ability of mycoplasmas to take up large quantities of cholesterol appears to be correlated with an ability to take up exogenous phospholipids. Isolated membranes of Mycoplasma capricolum and Acholeplasma laidlawii took up lower amounts of cholesterol than did membranes of growing cells and did not take up phospholipids. Inhibition of M. capricolum growth decreased the ability of the cells to take up exogenous phospholipids and cholesterol. The possibility that the contact between the lipid donors and the membrane involves specific receptors best exposed in actively growing cells is discussed. 相似文献
123.
Structural divergence among cannabinoids influences membrane dynamics: a 2H solid-state NMR analysis
Tiburu EK Bass CE Struppe JO Lorigan GA Avraham S Avraham HK 《Biochimica et biophysica acta》2007,1768(9):2049-2059
Cannabinoids are compounds that can modulate neuronal functions and immune responses via their activity at the CB(1) receptor. We used (2)H NMR order parameters and relaxation rate determination to delineate the behavior of magnetically aligned phospholipid bilayers in the presence of several structurally distinct cannabinoid ligands. THC (Delta(9)-Tetrahydrocannabinol) and WIN-55,212-2 were found to lower the phase transition temperature of the DMPC and to destabilize their acyl chains leading to a lower average S(CD) ( approximately 0.13), while methanandamide and CP-55,940 exhibited unusual properties within the lipid bilayer resulting in a greater average S(CD) ( approximately 0.14) at the top of the phospholipid upper chain. The CB(1) antagonist AM281 had average S(CD) values that were higher than the pure DMPC lipids, indicating a stabilization of the lipid bilayer. R(1Z) versus |S(CD)|(2) plots indicated that the membrane fluidity is increased in the presence of THC and WIN-55,212-2. The interaction of CP-55,940 with a variety of zwitterionic and charged membranes was also assessed. The unusual effect of CP-55,940 was present only in bicelles composed of DMPC. These studies strongly suggest that cannabinoid action on the membrane depends upon membrane composition as well as the structure of the cannabinoid ligands. 相似文献
124.
I. S. Sheremetev E. A. Petrunenko D. E. Kislov S. B. Rozenfeld I. A. Dmitriev L. Jargalsaikhan S. Enkh-Amgalan 《Contemporary Problems of Ecology》2017,10(1):17-27
This paper deals with food selectivity in large herbivores of Eastern Mongolia, its factors, and their impact on the herbivore community structure. It is shown that, due to the degradation of vegetation, all studied herbivores display a significant selectivity level conditioned by their morpho–physiological features and spatial distribution. The selectivity seems to provide competitive advantages but no food niche differentiation. We suppose that herbivore communities in Eastern Mongolia, both human-controlled and wild, bear an increase of the small browser portion under pasture degradation. This, in turn, increases the degradation rate. This cyclic interaction shows a possible mechanism for the formation of endogenous crises in herbivore communities and can explain features of extinction events of large herbivores of the “Mammoth fauna.” 相似文献
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128.
We propose a model of memory reconsolidation that can output new sentences with additional meaning after refining information
from input sentences and integrating them with related prior experience. Our model uses available technology to first disambiguate
the meanings of words and extracts information from the sentences into a structure that is an extension to semantic networks.
Within our long-term memory we introduce an action relationships database reminiscent of the way symbols are associated in
brain, and propose an adaptive mechanism for linking these actions with the different scenarios. The model then fills in the
implicit context of the input and predicts relevant activities that could occur in the context based on a statistical action
relationship database. The new data both of the more complete scenario and of the statistical relationships of the activities
are reconsolidated into memory. Experiments show that our model improves upon the existing reasoning tool suggested by MIT
Media lab, known as ConceptNet. 相似文献
129.
Tiburu EK Karp ES Birrane G Struppe JO Chu S Lorigan GA Avraham S Avraham HK 《Biochemistry》2006,45(23):7356-7365
Cannabinoid receptors are G-protein-coupled receptors comprised of seven transmembrane helices. We hypothesized that the extended helix of the receptor interacts differently with POPC bilayers due to the differing distribution of charged amino acid residues. To test this, hCB1(T377-E416) and hCB2(K278-H316) peptides were studied with 31P and 2H solid-state NMR spectroscopy by incorporating them into 1-palmitoyl-2-oleoyl-sn-glycerophosphocholine bilayers. Lipid affinities of the 40- and 39-residue peptides were analyzed on the basis of 31P and 2H spectral line shapes, order parameters, and T1 relaxation measurements of the POPC bilayers. Lipid headgroup perturbations were noticed in the 31P NMR spectra in the lipid/peptide mixtures when compared with the pure lipids. 2H order parameters were calculated from the quadrupolar splitting of the de-Paked 2H NMR spectra. At the top of the acyl chain, pure lipids had an average S(CD) approximately = 0.20, whereas S(CD) approximately = 0.16 and S(CD) approximately = 0.18 were found in the presence of hCB1(T377-E416) and hCB2(K278-H316), respectively. S(CD) values decreased in the central part of the acyl chains when compared to the pure POPC lipids, indicating a change in the dynamic properties of the lipid membrane in the presence of the cannabinoid peptides. R(1Z) vs S2(CD) plots exhibited a linear dependency with and without the peptides, with an increase in slope upon addition of the peptides to the POPC, indicating that the dynamics of the lipid bilayer is dominated by fast axially symmetric motion. This study provides insights into the interaction of cannabinoid peptides with the membrane bilayer by investigating the headgroup and acyl chain dynamics. 相似文献
130.
Magalhaes MA Larson DR Mader CC Bravo-Cordero JJ Gil-Henn H Oser M Chen X Koleske AJ Condeelis J 《The Journal of cell biology》2011,195(5):903-920
Invadopodia are invasive protrusions with proteolytic activity uniquely found in tumor cells. Cortactin phosphorylation is a key step during invadopodia maturation, regulating Nck1 binding and cofilin activity. The precise mechanism of cortactin-dependent cofilin regulation and the roles of this pathway in invadopodia maturation and cell invasion are not fully understood. We provide evidence that cortactin-cofilin binding is regulated by local pH changes at invadopodia that are mediated by the sodium-hydrogen exchanger NHE1. Furthermore, cortactin tyrosine phosphorylation mediates the recruitment of NHE1 to the invadopodium compartment, where it locally increases the pH to cause the release of cofilin from cortactin. We show that this mechanism involving cortactin phosphorylation, local pH increase, and cofilin activation regulates the dynamic cycles of invadopodium protrusion and retraction and is essential for cell invasion in 3D. Together, these findings identify a novel pH-dependent regulation of cell invasion. 相似文献