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71.
72.
The purpose of this research was to investigate the interaction of water with ethylcellulose samples and assess the effect
of particle size on the interaction. The distribution of water within coarse particle ethylcellulose (CPEC; average particle
size 310 μm) and fine particle ethylcellulose (FPEC; average particle size 9.7 μm) of 7 cps viscosity grade was assessed by
differential scanning calorimetry (DSC) and dynamic vapor sorption analysis. The amounts of nonfreezing and freezing water
in hydrated samples were determined from melting endotherms obtained by DSC. An increase in water content resulted in an increase
in the enthalpy of fusion of water for the two particle size fractions of EC. The amount of nonfreezable water was not affected
by the change in particle size at low water contents. Exposure of ethylcellulose to water for 30 minutes is sufficient to
achieve equilibration within the hydrated polymer at 47% wt/wt water content. The moisture sorption profiles were analyzed
according to the Guggenheim-Anderson-de Boer (GAB) and Young and Nelson equations, which can help to distinguish moisture
distribution in different physical forms. The amount of externally adsorbed moisture was greater in the case of FPEC. Internally
absorbed moisture was evident only with the CPEC. In light of these results, and explanation is offered for the success of
FPEC in wet-granulation methods where CPEC was not successful. 相似文献
73.
74.
G Nivaler EA Zimmerman R Defendini AS Liotta DT Kreiger MJ Brownstein 《The Journal of cell biology》1979,81(1):50-58
Adrenocorticotropin and β-lipotropin (β-LPH) have been localized by immunoperoxidase methods in nerve cells and fibers of the hypothalamus and brain stem of the ewe. 6-μm sections were immunostained first for either ACTH or β-LPH. The reaction products and the antibody complexes were then eluted completely from the tissue, and the same section was immunostained for the second peptide. Absorption of the primary antisera with a variety of peptide fragments of ACTH and β-LPH demonstrated, immunocytochemically as well as by radioimmunoassay, that the ACTH and β-LPH antisera were directed to the COOH- and NH(2)-termini of the peptides, respectively. Neither antiserum recognized any portion of the heterologous peptide. In the sequential staining procedure on the same tissue section, preincubation of the antisera with the homologous peptide abolished the staining, whereas preincubation with the heterologous peptide did not affect it, regardless of the order followed. Every nerve cell in the arcuate nucleus that contained ACTH also contained β-LPH, but β-LPH cells appeared, probably falsely, to be twice as numerous as ACTH cells. β-LPH-positive fibers in and beyond the hypothalamus were also more numerous and stained more intensively than ACTH fibers. The salient exception was fibers in the infundibular zona externa, where the opposite was true. Our observations establish that ACTH and β-LPH are contained in the same nerve cells They stongly favor biosynthesis in brain, probably from a common precursor molecule, as has been demonstrated in the pituitary gland. The complexity of the cytologic distribution pattern described suggests that the two peptides are not processed in the same manner by the nerve cell. 相似文献
75.
The origins of clot rheological behavior associated with network morphology and factor XIIIa-induced cross-linking were studied in fibrin clots. Network morphology was manipulated by varying the concentrations of fibrinogen, thrombin, and calcium ion, and cross-linking was controlled by a synthetic, active-center inhibitor of FXIIIa. Quantitative measurements of network features (fiber lengths, fiber diameters, and fiber and branching densities) were made by analyzing computerized three-dimensional models constructed from stereo pairs of scanning electron micrographs. Large fiber diameters and lengths were established only when branching was minimal, and increases in fiber length were generally associated with increases in fiber diameter. Junctions at which three fibers joined were the dominant branchpoint type. Viscoelastic properties of the clots were measured with a rheometer and were correlated with structural features of the networks. At constant fibrinogen but varying thrombin and calcium concentrations, maximal rigidities were established in samples (both cross-linked and noncross-linked) which displayed a balance between large fiber sizes and great branching. Clot rigidity was also enhanced by increasing fiber and branchpoint densities at greater fibrinogen concentrations. Network morphology is only minimally altered by the FXIIIa-catalyzed cross-linking reaction, which seems to augment clot rigidity most likely by the stiffening of existing fibers. 相似文献
76.
Identification and characterization of a prevacuolar compartment in stigmas of nicotiana alata 总被引:3,自引:1,他引:2
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The stigmas of the ornamental tobacco plant Nicotiana alata accumulate large quantities of a series of 6-kD proteinase inhibitors (PIs) in the central vacuole that are derived from a 40-kD precursor protein, Na-PI. The sorting information that directs Na-PI to the vacuole is likely to reside in a C-terminal propeptide domain of 25 amino acids that forms an amphipathic alpha helix. Using cell fractionation techniques, we have examined transit of Na-PI through the endomembrane system and have identified a prevacuolar compartment that contains Na-PI with an intact targeting signal. In contrast, the targeting signal is not present on the predominant form of Na-PI in the vacuole. The prevacuolar compartment is marked by the presence of homologs of both the t-SNARE, PEP12p, and the putative vacuolar sorting receptor BP-80. Cross-linking and affinity precipitation studies revealed that Na-PI associates with BP-80 within this compartment, providing in vivo evidence for the function of BP-80 as a sorting receptor for a protein with a C-terminal vacuolar targeting signal. 相似文献
77.
78.
Débora Guerini Souza Bruna Bellaver Gisele Hansel Bernardo Assein Arús Gabriela Bellaver Aline Longoni Janaina Kolling Angela T. S. Wyse Diogo Onofre Souza André Quincozes-Santos 《Neurochemical research》2016,41(7):1578-1586
Astrocytes are multitasking players in brain complexity, possessing several receptors and mechanisms to detect, participate and modulate neuronal communication. The functionality of astrocytes has been mainly unraveled through the study of primary astrocyte cultures, and recently our research group characterized a model of astrocyte cultures derived from adult Wistar rats. We, herein, aim to characterize other basal functions of these cells to explore the potential of this model for studying the adult brain. To characterize the astrocytic phenotype, we determined the presence of GFAP, GLAST and GLT 1 proteins in cells by immunofluorescence. Next, we determined the concentrations of thirteen amino acids, ATP, ADP, adenosine and calcium in astrocyte cultures, as well as the activities of Na+/K+-ATPase and acetylcholine esterase. Furthermore, we assessed the presence of the GABA transporter 1 (GAT 1) and cannabinoid receptor 1 (CB 1) in the astrocytes. Cells demonstrated the presence of glutamine, consistent with their role in the glutamate–glutamine cycle, as well as glutamate and d-serine, amino acids classically known to act as gliotransmitters. ATP was produced and released by the cells and ADP was consumed. Calcium levels were in agreement with those reported in the literature, as were the enzymatic activities measured. The presence of GAT 1 was detected, but the presence of CB 1 was not, suggesting a decreased neuroprotective capacity in adult astrocytes under in vitro conditions. Taken together, our results show cellular functionality regarding the astrocytic role in gliotransmission and neurotransmitter management since they are able to produce and release gliotransmitters and to modulate the cholinergic and GABAergic systems. 相似文献
79.
80.
A model of the carbohydrate recognition domain CRD, residues 111-245, of
hamster galectin-3 has been made using homology modeling and dynamics
minimization methods. The model is based on the known x-ray structures of
bovine galectin-1 and human galectin-2. The oligosaccharides
NeuNAc-alpha2,3-Gal-beta1,4-Glc and GalNAc-alpha1, 3-
[Fuc-alpha1,2]-Gal-beta1,4-Glc, known to be specific high-affinity ligands
for galectin-3, as well as lactose recognized by all galectins were docked
in the galectin-3 CRD model structure and a minimized binding conformation
found in each case. These studies indicate a putative extended
carbohydrate-binding subsite in the hamster galectin- 3 involving Arg139,
Glu230, and Ser232 for NeuNAc-alpha2,3-; Arg139 and Glu160 for
fucose-alpha1,2-; and Arg139 and Ile141 for GalNAc-alpha1,3- substituents
on the primary galactose. Each of these positions is variable within the
whole galectin family. Two of these residues, Arg139 and Ser232, were
selected for mutagenesis to probe their importance in this newly identified
putative subsite. Residue 139 adopts main-chain dihedral angles
characteristic of an isolated bridge structural feature, while residue 232
is the C-terminal residue of beta- strand-11, and is followed immediately
by an inverse gamma-turn. A systematic series of mutant proteins have been
prepared to represent the residue variation present in the aligned
sequences of galectins-1, - 2, and -3. Minimized docked models were
generated for each mutant in complex with NeuNAc-alpha2,3-Gal-beta1,4-Glc,
GalNAc-alpha1, 3-[Fuc- alpha1,2]-Gal-beta1,4- Glc, and Gal-beta1,4-Glc.
Correlation of the computed protein-carbohydrate interaction energies for
each lectin- oligosaccharide pair with the experimentally determined
binding affinities for fetuin and asialofetuin or the relative potencies of
lactose and sialyllactose in inhibiting binding to asiolofetuin is
consistent with the postulated key importance of Arg139 in recognition of
the extended sialylated ligand.
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