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排序方式: 共有82条查询结果,搜索用时 15 毫秒
1.
Cecilia PC Soh Alastair SR Donald James Feeney Walter TJ Morgan Winifred M Watkins 《Glycoconjugate journal》1989,6(3):319-332
The tetrasaccharides GalNAcß1-4[NeuAc2-3]Galß1-4Glc and GalNAcß1-4[NeuAc2-3]Galß1-4GlcNAc were synthesised by enzymic transfer of GalNAc from UDP-GalNAc to 3-sialyllactose (NeuAc2-3Galß1-4Glc) and 3-sialyl-N-acetyllactosamine (NeuAc2-3Galß1-4GlcNAc). The structures of the products were established by methylation and1H-500 MHz NMR spectroscopy. In Sda serological tests the product formed with 3-sialyl-N-acetyllactosamine was highly active whereas that formed with 3-sialyllactose had only weak activity. 相似文献
2.
Acrosome reaction of bovine spermatozoa in vivo: sites and effects of stages of the estrous cycle 总被引:3,自引:0,他引:3
Thirty-two cows were inseminated near the uterotubal junction at various stages of the estrous cycle and slaughtered 16 h later to determine the effects of stage of the estrous cycle and tubal site of sperm recovery on the frequency of acrosome-reacted bull spermatozoa. Slaughter times were 46, 70, 144, or 168 h after each cow was injected with prostaglandin (PG) F 2 alpha or during the luteal phase of the estrous cycle. Sperm were recovered from the upper uterus and the isthmus and ampulla of the oviducts and stained for both viability and acrosome reaction. The highest frequency of acrosome-reacted sperm was found in the ampulla ipsilateral to a dominant follicle (largest follicle present) or recent ovulation and primarily at 70 h after PGF2 alpha (P less than 0.05). Also, fewer sperm were acrosome reacted prior to (46 h post-PGF2 alpha) and well after (168 h post-PGF2 alpha) estrus than during or immediately postestrus (70, 90, and 144 h post-PGF2 alpha; P less than 0.05). Except for two cows, one at 46 h and one at 70 h, all cows with more than 50% acrosome-reacted sperm in the ampulla had ovulated before slaughter. These data suggest that capacitated sperm become localized in the ampulla of the oviduct of the ovulatory side around the time of ovulation. 相似文献
3.
Glyoxylate and glutamate effects on photosynthetic carbon metabolism in isolated chloroplasts and mesophyll cells of spinach 总被引:6,自引:3,他引:3
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Addition of millimolar sodium glyoxylate to spinach (Spinacia oleracea) chloroplasts was inhibitory to photosynthetic incorporation of 14CO2 under conditions of both low (0.2 millimolar or air levels) and high (9 millimolar) CO2 concentrations. Incorporation of 14C into most metabolites decreased. Labeling of 6-P-gluconate and fructose-1,6-bis-P increased. This suggested that glyoxylate inhibited photosynthetic carbon metabolism indirectly by decreasing the reducing potential of chloroplasts through reduction of glyoxylate to glycolate. This hypothesis was supported by measuring the reduction of [14C]glyoxylate by chloroplasts. Incubation of isolated mesophyll cells with glyoxylate had no effect on net photosynthetic CO2 uptake, but increased labeling was observed in 6-P-gluconate, a key indicator of decreased reducing potential. The possibility that glyoxylate was affecting photosynthetic metabolism by decreasing chloroplast pH cannot be excluded. Increased 14C-labeling of ribulose-1,5-bis-P and decreased 3-P-glyceric acid and glycolate labeling upon addition of glyoxylate to chloroplasts suggested that ribulose-bis-P carboxylase and oxygenase might be inhibited either indirectly or directly by glyoxylate. Glyoxylate addition decreased 14CO2 labeling into glycolate and glycine by isolated mesophyll cells but had no effect on net 14CO2 fixation. Glutamate had little effect on net photosynthetic metabolism in chloroplast preparations but did increase 14CO2 incorporation by 15% in isolated mesophyll cells under air levels of CO2. 相似文献
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Approaches to breeding for salinity tolerance - a case study on Porteresia coarctata 总被引:2,自引:0,他引:2
R LATHA C SRINIVAS RAO H M SR SUBRAMANIAM P EGANATHAN M S SWAMINATHAN 《The Annals of applied biology》2004,144(2):177-184
Cereals are the world's major source of food for human nutrition. Among these, rice (Oryza sativa) is the most prominent and represents the staple diet for more than two-fifths (2.4 billion) of the world's population, making it the most important food crop of the developing world (Anon., 2000a). Rice production in vast stretches of coastal areas is hampered due to high soil salinity. This is because rice is a glycophyte and it does not grow well under saline conditions. In order to increase rice production in these areas there is a need to develop rice varieties suited to saline environments. Research has shown that Porteresia coarctata, a highly salt tolerant wild relative of rice growing in estuarine soils, is an important material for transferring salt tolerant characteristics to rice. It is quite possible that Porteresia may be used as a parent for evolving better and truly salt resistant varieties. The inadequate results and the difficulties associated with conventional breeding techniques necessitate the use of the tools of crop biotechnology in unravelling some of the characteristics of Porteresia that have been highlighted in this report. In view of the limited resources available for increasing salinity tolerance to the breeders to wild rice germplasm, Porteresia is undoubtedly one of the key source species for elevating salinity tolerance in cultivated rice. 相似文献
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The effect of neurotensin on submaximally-stimulated hepatobiliary and pancreatic secretion was studied in 6 healthy subjects. An intravenous infusion of neurotensin 1.4 ± 0.3 pmol/kg/min, designed to reproduce plasma neurotensin immunoreactivity levels within the physiological range, produced a significant increase in pancreatic bicarbonate output. Plasma concentrations of pancreatic polypeptide rose by 83 ± 16 pmol/l and were associated with a small reduction in trypsin, but no significant change in bilirubin outputs. 相似文献
9.
Effects of carbon dioxide and oxygen on the regulation of photosynthetic carbon metabolism by ammonia in spinach mesophyll cells 总被引:9,自引:9,他引:0
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Photosynthetic carbon metabolism of isolated spinach mesophyll cells was characterized under conditions favoring photorespiratory (PR; 0.04% CO2 and 20% O2) and nonphotorespiratory (NPR; 0.2% CO2 and 2% O2) metabolism, as well as intermediate conditions. Comparisons were made between the metabolic effects of extracellularly supplied NH4+ and intracellular NH4+, produced primarily via PR metabolism. The metabolic effects of 14CO2 fixation under PR conditions were similar to perturbations of photosynthetic metabolism brought about by externally supplied NH4+; both increased labeling and intracellular concentrations of glutamine at the expense of glutamate and increased anaplerotic synthesis through α-ketoglutarate. The metabolic effects of added NH4+ during NPR fixation were greater than those during PR fixation, presumably due to lower initial NH4+ levels during NPR fixation. During PR fixation, addition of ammonia caused decreased pools and labeling of glutamate and serine and increased glycolate, glyoxylate, and glycine labeling. The glycolate pathway was thus affected by increased rates of carbon flow and decreased glutamate availability for glyoxylate transamination, resulting in increased usage of serine for transamination. Sucrose labeling decreased with NH4+ addition only during PR fixation, suggesting that higher photosynthetic rates under NPR conditions can accommodate the increased drain of carbon toward amino acid synthesis while maintaining sucrose synthesis. 相似文献
10.
The orbitofrontal cortex (OFC) and piriform cortex are involved in encoding the predictive value of olfactory stimuli in rats, and neural responses to olfactory stimuli in these areas change as associations are learned. This experience-dependent plasticity mirrors task-related changes previously observed in mesocortical dopamine neurons, which have been implicated in learning the predictive value of cues. Although forms of associative learning can be found at all ages, cortical dopamine projections do not mature until after postnatal day 35 in the rat. We hypothesized that these changes in dopamine circuitry during the juvenile and adolescent periods would result in age-dependent differences in learning the predictive value of environmental cues. Using an odor-guided associative learning task, we found that adolescent rats learn the association between an odor and a palatable reward significantly more slowly than either juvenile or adult rats. Further, adolescent rats displayed greater distractibility during the task than either juvenile or adult rats. Using real-time quantitative PCR and immunohistochemical methods, we observed that the behavioral deficit in adolescence coincides with a significant increase in D1 dopamine receptor expression compared to juvenile rats in both the OFC and piriform cortex. Further, we found that both the slower learning and increased distractibility exhibited in adolescence could be alleviated by experience with the association task as a juvenile, or by an acute administration of a low dose of either the dopamine D1 receptor agonist SKF-38393 or the D2 receptor antagonist eticlopride. These results suggest that dopaminergic modulation of cortical function may be important for learning the predictive value of environmental stimuli, and that developmental changes in cortical dopaminergic circuitry may underlie age-related differences in associative learning. 相似文献