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41.
NADH diferric transferrin reductase in liver plasma membrane 总被引:6,自引:0,他引:6
I L Sun P Navas F L Crane D J Morré H L?w 《The Journal of biological chemistry》1987,262(33):15915-15921
Evidence is presented that rat liver plasma membranes contain a distinct NADH diferric transferrin reductase. Three different assay procedures for demonstration of the activity are described. The enzyme activity is highest in isolated plasma membrane, and activity in other internal membranes is one-eighth or less than in plasma membrane. The activity is inhibited by apotransferrin and antitransferrin antibodies. Trypsin treatment of the membranes leads to rapid loss of the transferrin reductase activity as compared with NADH ferricyanide reductase activity. Erythrocyte plasma membranes, which lack transferrin receptors, show no diferric transferrin reductase activity, although NADH ferricyanide reductase is present. The transferrin reductase is inhibited by agents that inhibit diferric transferrin reduction by intact cells and is activated by CHAPS (3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfate) detergent. Inhibitors of mitochondrial electron transport have no effect on the activity. We propose that the NADH diferric transferrin reductase in plasma membranes measures the activity of the enzyme that causes the reduction of diferric transferrin by intact cells. This transmembrane electron transport system requires the transferrin receptor for diferric transferrin reduction. Because the transmembrane electron transport has been shown to stimulate cell growth, the reduction of diferric transferrin at the cell surface may be an important function for diferric transferrin in stimulation of cell growth, in addition to its role in iron transport. 相似文献
42.
Isolation and reconstitution of the dicyclohexylcarbodiimide-sensitive proton pore of the clathrin-coated vesicle proton translocating complex 总被引:13,自引:0,他引:13
The clathrin-coated vesicle proton translocating complex is composed of a maximum of eight polypeptides. The function of the components of this system have not been defined. Proton pumping catalyzed by the reconstituted, 200-fold purified proton translocating complex of clathrin-coated vesicles is inhibited 50% at a dicyclohexylcarbodiimide (DCCD)/protein ratio of 0.66 mumol of DCCD/mg of protein. At an identical DCCD/protein ratio, the 17-kDa component of the proton pump is labeled by [14C]DCCD. Through toluene extraction, the 17-kDa subunit has been isolated from the holoenzyme. The 17-kDa polypeptide diminished proteoliposome acidification when coreconstituted with either bacteriorhodopsin or the intact clathrin-coated vesicle proton translocating ATPase. In both instances, treatment of the 17-kDa polypeptide with DCCD restored proteoliposome acidification. Moreover, the proton-conducting activity of the 17-kDa polypeptide is abolished by trypsin digestion. These results demonstrate that the 17-kDa polypeptide present in the isolated proton ATPase of clathrin-coated vesicles is a subunit which functions as a transmembranous proton pore. 相似文献
43.
This paper reports the experimental transmission of a bird parasite into jirds. Infective larvae of Cardiofilaria nilesi obtained from laboratory colonized Coquillettidia crassipes mosquitoes which had fed on an infected chicken were inoculated subcutaneously into jirds. The number of larvae per jird varied from 10 to 228. Microfilaraemia appeared 22 to 89 days after inoculation of the infective larvae. Experiments were carried out with 24 jirds through six generations extending over a period of 22 months and 17 produced patent infections. At present 8 infected jirds are being maintained in the laboratory; their patent periods ranging from 6 to 13 months. However, the longest patent period observed was about thirteen months. The percentage of adults recovered in autopsied jirds ranged from 0 to 40 with an average of 16. The chicken showed a microfilarial periodicity with the peak microfilarial density around 2200 hours. However, in jirds there was a change in sub-periodicity. This model in the jird may be very useful for the screening of filaricides and in immunological work. 相似文献
44.
利用 XAD-4憎水性吸附树脂采集墨红头香,以毛细管气相色谱双柱保留指数和 GC/MS/DS 联用方法鉴定头香的化学成份。共分离鉴定或初步鉴定了45种组份,其中含量较大的有乙酸芳樟酯(14.98%),柠檬烯(12.07%),甲基苯甲醚(9.88%),香茅醇(4.82%),乙酸巳酯(3.98%),β-石竹烯(4.55%),芳樟醇(3.18%),正巳醇(3.17%)等. 相似文献
45.
Nina Safar-Hermann Mohammed N. Ismail Han Sun Choi Erich Mstl Elmar Bamberg 《Zoo biology》1987,6(2):189-193
Estrogen concentration in feces was investigated in five different herbivorous species of zoo animals. Using a nonspecific estrogen radioimmunoassay, in four species (red buffalo, yak, Grevy's zebra, and Nubian ibex) pregnancy was revealed by measuring estrogen concentration in feces. In hippopotamus, the levels of fecal estrogens were not different between pregnant and nonpregnant animals. 相似文献
46.
L Sun G Serrero A Piltch J Hayashi 《Biochemical and biophysical research communications》1987,148(2):603-608
Thymic endocrine epithelial cell line TEA3A1 can be maintained and passaged in a serum-free WAJC404A medium supplemented with insulin, transferrin, dexamethasone and EGF. EGF not only promotes the growth of these cells but also regulates the activation of phospholipase A2 enzyme activity. The binding of [125I]EGF to the TEA3A1 cells is temperature and time dependent, saturable and can be blocked by excess unlabelled EGF. Two classes of EGF receptors are found on these cells. One with Kd of 5 X 10(-11)M (approximately 3000 sites/cell) and the other with Kd of 5 X 10(-9)M (approximately 30,000 sites/cell). The resynthesis of EGF receptor in TEA3A1 cells after down-regulation requires about 24 hrs and can be blocked by both actinomycin D and cycloheximide. 相似文献
47.
A difference in the expression and metabolism of sulfated glycosaminoglycans between rat mammary tumor cells derived from a primary tumor and those from its metastatic lesions has been observed. Cells from the primary tumor possessed about equal quantities of chondroitin sulfate and heparan sulfate on their cell surfaces but released fourfold more chondroitin sulfate than heparan sulfate into their medium. In contrast, cells from distal metastatic lesions expressed approximately 5 times more heparan sulfate than chondroitin sulfate in both medium and cell surface fractions. This was observed to be the result of differential synthesis of the glycosaminoglycans and not of major structural alterations of the individual glycosaminoglycans. The degree of sulfation and size of heparan sulfate were similar for all cells examined. However, chondroitin sulfate, observed to be only chondroitin 4-sulfate, from the metastases-derived cells had a smaller average molecular weight on gel filtration chromatography and showed a decreased quantity of sulfated disaccharides upon degradation with chondroitin ABC lyase compared to the primary tumor derived cells. Major qualitative or quantitative alterations were not observed for hyaluronic acid among the various 13762NF cells. The metabolism of newly synthesized sulfated glycosaminoglycans was also different between cells from primary tumor and metastases. Cells from the primary tumor continued to accumulate glycosaminoglycans in their medium over a 72-h period, while the accumulation of sulfated glycosaminoglycans in the medium of metastases-derived cells showed a plateau after 18-24 h. A pulse-chase kinetics study demonstrated that both heparan sulfate and chondroitin sulfate were degraded by the metastases-derived cells, whereas the primary tumor derived cells degraded only heparan sulfate and degraded it at a slower rate.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
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