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排序方式: 共有594条查询结果,搜索用时 15 毫秒
1.
Yiwen Sun Zexuan Zhu Siping Chen Jega Balakrishnan Derek Abbott Anil T. Ahuja Emma Pickwell-MacPherson 《PloS one》2012,7(11)
The GP2 peptide is derived from the Human Epidermal growth factor Receptor 2 (HER2/nue), a marker protein for breast cancer present in saliva. In this paper we study the temperature dependent behavior of hydrated GP2 at terahertz frequencies and find that the peptide undergoes a dynamic transition between 200 and 220 K. By fitting suitable molecular models to the frequency response we determine the molecular processes involved above and below the transition temperature (T
D). In particular, we show that below T
D the dynamic transition is dominated by a simple harmonic vibration with a slow and temperature dependent relaxation time constant and that above T
D, the dynamic behavior is governed by two oscillators, one of which has a fast and temperature independent relaxation time constant and the other of which is a heavily damped oscillator with a slow and temperature dependent time constant. Furthermore a red shifting of the characteristic frequency of the damped oscillator was observed, confirming the presence of a non-harmonic vibration potential. Our measurements and modeling of GP2 highlight the unique capabilities of THz spectroscopy for protein characterization. 相似文献
2.
Summary This paper presents the preliminary observations on the interstitial fauna of the south-west coast of India, made during the course of 1963–1964. Observations were made at four stations representing different ecological habitats. The influence of some factors, such as wave action, grain size, temperature and salinity on the fauna was studied. The occurrence, seasonal abundance and the nature of distribution of the different groups on the intertidal zone, were also studied at the four stations. 相似文献
3.
Blood serum total cholesterol levels of crossbred Taur-indicus donor cows (n=22), in their 1st to 4th parity, were studied as an indicator of embryo yield. These cows were superovulated either with FSH or PMSG + anti-PMSG on the 12th day of the synchronized estrous cycle. The total and transferable number of embryos did not differ significantly between the treatment groups. The number of corpora lutea and total and transferable embryos in donors having total cholesterol levels <140 mg/dl were significantly (P < 0.05) lower than those of cows having >140 mg/dl, indicating that low total cholesterol levels might adversely affect superovulatory response. Thus, estimation of total cholesterol concentrations of potential donors can be a useful tool for predicting superovulatory responses. 相似文献
4.
Krishna Balakrishnan Frank J. Hsu Dean G. Hafeman Harden M. McConnell 《Biochimica et Biophysica Acta (BBA)/Molecular Cell Research》1982,721(1):30-38
The isolation and characterization of a hybridoma cell line producing a monoclonal IgG1 antibody against a spin-label nitroxide group is described. The antibody recognizes a synthetic hapten containing linked dinitrophenyl and 2,2,6,6-tetramethylpiperidinyl 1-oxy groups, having an affinity of 3.6±1.0·106 M?1 for the soluble hapten at 25°C. The antibody binds to phospholipid vesicles containing 2 mol% of spin label-derivitized lipid (lipid hapten) with an affinity of 1.5±0.2·108 M?1. This monoclonal IgG1 mediates the binding of hapten-bearing lipid vesicles to mouse macrophage RAW264 cells bearing Fc receptors. The cellular responses to this binding are similar to those observed previously using polyclonal rabbit anti-hapten IgG. As with the heterogeneous antibodies, the monoclonal IgG1 is more efficient in mediating cellular uptake when the vesicles are in the ‘fluid’ physical state (dimyristoylphosphatidylcholine at 37°C) compared to ‘solid’ (dipalmitoylphosphatidylcholine at 37°C). Despite the enhanced binding of ‘fluid’ phospholipid vesicles to cells, only the ‘solid’ vesicles triggered a significant respiratory burst in RAW264 macrophages. 相似文献
5.
Exploring polyethylenimine-mediated DNA transfection and the proton sponge hypothesis 总被引:6,自引:0,他引:6
BACKGROUND: The relatively high transfection efficiency of polyethylenimine (PEI) vectors has been hypothesized to be due to their ability to avoid trafficking to degradative lysosomes. According to the proton sponge hypothesis, the buffering capacity of PEI leads to osmotic swelling and rupture of endosomes, resulting in the release of the vector into the cytoplasm. METHODS: The mechanism of PEI-mediated DNA transfer was investigated using quantitative methods to study individual steps in the overall transfection process. In addition to transfection efficiency, the cellular uptake, local pH environment, and stability of vectors were analyzed. N-Quaternized (and therefore non-proton sponge) versions of PEI and specific cell function inhibitors were used to further probe the proton sponge hypothesis. RESULTS: Both N-quaternization and the use of bafilomycin A1 (a vacuolar proton pump inhibitor) reduced the transfection efficiency of PEI by approximately two orders of magnitude. Chloroquine, which buffers lysosomes, enhanced the transfection efficiency of N-quaternized PEIs and polylysine by 2-3-fold. In contrast, chloroquine did not improve the transfection efficiency of PEI. The measured average pH environment of PEI vectors was 6.1, indicating that they successfully avoid trafficking to acidic lysosomes. Significantly lower average pH environments were observed for permethyl-PEI (pH 5.4), perethyl-PEI (pH 5.1), and polylysine (pH 4.6) vectors. Cellular uptake levels of permethyl-PEI and perethyl-PEI vectors were found to be 20 and 90% higher, respectively, than that of parent PEI vectors, indicating that the reduction in transfection activity of the N-quaternized PEIs is due to a barrier downstream of cellular uptake. A polycation/DNA-binding affinity assessment showed that the more charge dense N-quaternized PEIs bind DNA less tightly than PEI, demonstrating that poor vector unpackaging was not responsible for the reduced transfection activity of the N-quaternized PEIs. CONCLUSIONS: The results obtained are consistent with the proton sponge hypothesis and strongly suggest that the transfection activity of PEI vectors is due to their unique ability to avoid acidic lysosomes. 相似文献
6.
Genetic localization and in vivo characterization of a Monascus azaphilone pigment biosynthetic gene cluster 总被引:1,自引:0,他引:1
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9.
Glyphidrilus annandalei Michaelson exhibits a pronounced breeding period extending from September to November. Breeding individuals achieve their maximum frequency in September, when 50 per cent of the whole population was with fully developed clitellum. Studies on the physical and chemical conditions of the habitat revealed that breeding in this worm depends the monsoon of the area creating optimum conditions for the life and activities of the organism. 相似文献
10.
Anita Balakrishnan Adam T. Stearns Peter J. Park Jonathan M. Dreyfuss David B. Rhoads Ali Tavakkolizadeh 《Experimental cell research》2010,316(20):3512-3521