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991.
992.
993.
The effect of negative surface charge and hydrophilic groups on liposome clearance from blood was investigated in mice using liposome-entrapped 67gallium-deferoxamine as a label. The presence of negatively-charged lipids may retard or accelerate liposome clearance. Physicochemical features contributing to optimal retardation of liposome clearance include a hydrophilic carbohydrate moiety and a sterically hindered negatively-charged group. The relevance of the negative charge steric effect is suggested by the finding that phosphatidylinositol phosphate (PIP) and trisialoganglioside (GT1) are less effective than phosphatidylinositol (PI) and monosialoganglioside (GM1), respectively, in retarding liposome clearance. The need for negative charge in addition to the carbohydrate group for optimal effect on retardation of clearance is indicated by the observation that asialoganglioside (AGM1) is less effective than GM1 in this respect. The negative charge effect is observed with liposome bilayers having both low and high temperature phase-transitions. Increasing the molar fraction of negatively-charged lipid (hydrogenated PI derived from soya) from 23 to 41% resulted in a dramatic acceleration of liposome clearance. The clearance-accelerating effect of the high negative charge was specifically directed to the liver with selective reduction of spleen uptake. Increasing liposome size also had an accelerating effect on clearance but in this case it was accompanied by a non-specific concomitant increase of both liver and spleen uptake. 相似文献
994.
Assembly of the F1 portion of the proton-translocating ATPase of Escherichia coli was examined in vivo. Analysis of strains lacking genes which specify the Fo polypeptides a, b, and c showed that the F1 subunits were able to assemble into a complex in the absence of the Fo subunits. In addition we have investigated the effects of mutations in the individual genes which specify the F1 polypeptides on the assembly process. Mutations of the uncA(alpha), uncG(gamma), or uncD(beta) genes result in a defective assembly of the F1 complex. In contrast, mutations in the uncH(delta) or uncC(epsilon) genes did not prevent assembly of the core alpha beta gamma complex. In these cases, however, the partial F1 complexes were incapable of restoring energy-linked functions to F1-depleted membranes. 相似文献
995.
In vivo cellular responses to electrophoretically applied dynorphin in the rat hippocampus 总被引:1,自引:0,他引:1
Recent immunohistochemical and radioimmunochemical observations have demonstrated a differential distribution of immunoreactive dynorphin (DYN) in rat brain. The presence of DYN immunoreactivity in a major intrinsic fiber pathway within the rat hippocampus (the mossy fiber system) has led us to evaluate the possible role of DYN and other closely related peptides in this structure. Single cell activity and hippocampal field potentials have been recorded from the CA1-CA3 cellular fields in halothane or urethane anesthetized rats. DYN, DYN1-13, DYN1-8, and alpha-neo-endorphin had an excitatory effect on most CA1-CA3 neurons encountered as has been previously observed for opiates and other opioid peptides. This response could be blocked by naloxone or by co-administration of Mg++ ion suggesting an indirect (synaptic) mechanism of excitation similar to that hypothetized for enkephalin. A significant number of CA3 neurons, however, exhibited a non-naloxone sensitive inhibitory response to DYN, related opioid peptides, and the kappa agonist WIN 35-197 (ethylketocyclazocine). Field potential analysis of CA1-CA3 neuronal responses to mossy fiber activation also indicated an excitatory, Mg++ reversible, action of iontophoretically applied DYN. These observations support our cytochemical and assay studies indicating diverse opioid systems within the rat hippocampus. In addition, these functional studies are congruent with other evidence suggesting multiple opioid mechanisms in this structure. 相似文献
996.
997.
Radiation inactivation target size of rat adipocyte glucose transporters in the plasma membrane and intracellular pools 总被引:1,自引:0,他引:1
D B Jacobs C J Berenski R A Spangler C Y Jung 《The Journal of biological chemistry》1987,262(17):8084-8087
The in situ assembly states of the glucose transport carrier protein in the plasma membrane and in the intracellular (microsomal) storage pool of rat adipocytes were assessed by studying radiation-induced inactivation of the D-glucose-sensitive cytochalasin B binding activities. High energy radiation inactivated the glucose-sensitive cytochalasin B binding of each of these membrane preparations by reducing the total number of the binding sites without affecting the dissociation constant. The reduction in total number of binding sites was analyzed as a function of radiation dose based on target theory, from which a radiation-sensitive mass (target size) was calculated. When the plasma membranes of insulin-treated adipocytes were used, a target size of approximately 58,000 daltons was obtained. For adipocyte microsomal membranes, we obtained target sizes of approximately 112,000 and 109,000 daltons prior to and after insulin treatment, respectively. In the case of microsomal membranes, however, inactivation data showed anomalously low radiation sensitivities at low radiation doses, which may be interpreted as indicating the presence of a radiation-sensitive inhibitor. These results suggest that the adipocyte glucose transporter occurs as a monomer in the plasma membrane while existing in the intracellular reserve pool either as a homodimer or as a stoichiometric complex with a protein of an approximately equal size. 相似文献
998.
B M Austen C J Evans D G Smyth 《Biochemical and biophysical research communications》1979,91(4):1211-1217
Peptide fragments derived from the NH2-terminus of corticotropin were found to exhibit widely differing degrees of stability to degradation by aminopeptidase M. Corticotropin itself was 135 times more stable than its NH2-terminal pentapeptide, and similar differences in stability were observed with peptides derived from the B-chain of bovine insulin. Enkephalin linked covalently to the A-chain of bovine insulin was at least 100 times more stable than the pentapeptide. The results demonstrate that the molecular size of a peptide is one factor that determines its NH2-terminal stability. 相似文献
999.
Rhodnius prolixus 5th instar nymphs have significant PO enzymatic activity in the anterior midgut, fat body and hemolymph. The tissue with the major amount of PO activity is the anterior midgut while those with higher specific activities are the fat body and hemolymph. In this work the temporal pattern of PO enzymatic activity in different tissues was investigated. In fat body, PO peaks occur at 7, 12 and 16 days after a blood meal. In hemolymph, PO diminishes until day 7, and then recovers by day 14. In the anterior midgut tissue, PO peaks on day 9 and just before ecdysis; a similar pattern was observed in the anterior midgut contents. Some of these activities are dependent on the release of ecdysone, as feeding blood meal containing azadirachtin suppresses them and ecdysone treatment counteracts this effect. These results suggest that during the development of the 5th instar, the insect has natural regulating cycles of basal PO expression and activation, which could be related to the occurrence of natural infections. The differences in temporal patterns of activity and the effects of azadirachtin and ecdysone in each organ suggest that, at least in R. prolixus, different tissues are expressing different PO genes. 相似文献
1000.
K D Croft J P Codde A Barden R Vandongen L J Beilin 《Biochimica et biophysica acta》1985,834(3):316-323
A synthetic diet preparation supplemented with 10% by weight of either safflower oil, hydrogenated coconut oil containing 3% safflower oil, or 'max EPA' fish oil was fed to rats over a 8-week period. Serial measurements of serum fatty acids, serum thromboxane B2 and urinary prostaglandin excretion were taken during the treatment period to assess the rate of change in fatty acid composition and prostaglandin synthesis following dietary manipulation. There was no significant change in weight gain between the dietary groups during the treatment period. Significant changes in serum fatty acids occurred within 48 h of treatment, with the 'max EPA' oil group having arachidonic acid levels reduced by 23% (P less than 0.01) compared to the coconut oil group. Conversely, rats fed safflower oil had an 18% enhancement of arachidonic acid during the same time period. Whole blood synthesis of thromboxane B2 was significantly depressed (P less than 0.01) after 48 h in rats fed 'max EPA' oil compared to the safflower oil or coconut oil groups. This suppression reached a maximum of 65% (P less than 0.001) after 7 days of dietary 'max EPA' oil treatment. The safflower oil and coconut oil-fed groups showed the same levels of serum thromboxane B2 production over the treatment period. Urinary excretion of both 6-ketoprostaglandin F1 alpha and prostaglandin E2 varied significantly (P less than 0.01) between the groups after 7 days of dietary treatment. Rats fed 'max EPA' oil had depressed urinary prostanoid excretion compared to the safflower and coconut oil groups which remained very similar to each other. After the 8-week treatment period rats were killed and the phospholipid fatty acid composition and prostaglandin-generating capacity of platelets, aorta and renal tissue was examined. Prostanoid production by kidney cortex and medulla and segments of aorta was consistently suppressed in rats fed 'max EPA' oil. These observations correlated well with changes in the phospholipid fatty acid profiles in these tissues. This study shows rapid changes in serum fatty acids and thromboxane B2 generation following dietary manipulation, while changes in urinary excretion or prostanoid metabolites occur only after a longer time period. 相似文献