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2.
Structures using X-ray diffraction data collected to 1.5-A resolution have been determined for the protein ribonuclease-A at nine different temperatures ranging from 98 to 320 K. It is determined that the protein molecule expands slightly (0.4% per 100 K) with increasing temperature and that this expansion is linear. The expansion is due primarily to subtle repacking of the molecule, with exposed and mobile loop regions exhibiting the largest movements. Individual atomic Debye-Waller factors exhibit predominantly biphasic behavior, with a small positive slope at low temperatures and a larger positive slope at higher temperatures. The break in this curve occurs at a characteristic temperature of 180-200 K, perhaps indicative of fundamental changes in the dynamical structure of the surrounding protein solvent. The distribution of protein Debye-Waller factors is observed to broaden as well as shift to higher values as the temperature is increased. 相似文献
3.
Effect of concentration quenching on fluorescence recovery after photobleaching measurements. 总被引:1,自引:1,他引:0
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Standard analysis of fluorescence recovery after photobleaching (FRAP) data is valid only if the quantum yield of unphotobleached fluorophores is independent of concentration, yet close molecular packing in two-dimensional systems may lead to significant fluorescence concentration quenching. Using total internal reflection fluorescence, we quantified the surface concentration dependence of the relative quantum yield of fluorescein isothiocyanate-labeled proteins adsorbed to polymeric surfaces before performing measurements of fluorescence recovery after pattern photobleaching. Adsorbed layers of FITC-labeled ribonuclease A displayed significant concentration quenching, and thus the standard FRAP analysis method was unacceptable. We present an extended FRAP analysis procedure that accounts for the changing quantum yield of diffusing fluorophores in systems that are influenced by concentration quenching. The extended analysis shows that if concentration quenching conditions prevail, there may be significant error in the transport parameters obtained from FRAP measurements by using the standard procedures. 相似文献
4.
Surface diffusion of interacting proteins. Effect of concentration on the lateral mobility of adsorbed bovine serum albumin. 总被引:5,自引:5,他引:0
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Surface diffusion of bovine serum albumin absorbed from aqueous solution to poly(methylmethacrylate) surfaces is significantly hindered by protein-protein lateral interactions. The long-time self diffusion coefficient measured by fluorescence recovery after pattern photobleaching decreases by approximately one order of magnitude as the surface area fraction occupied by protein increases from 0.10 to 0.69. Qualitative features of the surface concentration dependence of the self diffusion coefficient can be described by several recent models for lateral diffusion of interacting species. The mobile fraction is independent of the surface concentration, and both the self diffusion coefficient and the mobile fraction are constant between 15 min and 7 h of adsorption. 相似文献
5.
Two experiments were conducted to study the time of occurrence of the preovulatory LH surge in pigs. Sampling every ten minutes in six cycling gilts before and after onset of standing estrus revealed the preovulatory surge began from 8 hr before to 12 hr after the lordosis reflex was elicited. Three of six gilts initiated the preovulatory LH release coincident with the onset of estrus. Data from 28 postpartum sows, with samples drawn every six hours commencing with the onset of estrus, indicated maximum LH levels were present at the first observance of estrus. Six of the 28 sows had an LH peak 18-24 hr after the onset of estrus. 相似文献
6.
Using Saccharomyces cerevisiae as a demonstration system, we present a method to form two-dimensional, patternable cellular arrays. The method does not require surface chemical templating of the substratum to produce arrays or patterns. By virtue of their colloidal characteristics, S. cerevisiae cells may be induced to form dense, quasi-ordered two-dimensional clusters adjacent to an electrode surface by electrophoretic deposition (EPD). Using ac EPD, dense two-dimensional cell clusters may be formed in minutes from extremely dilute cell suspensions. The arrays may be induced to form geometric patterns by focusing the electric field during deposition. These monolayer arrays are reversible, dissipating by diffusion on removal of the electric field, and are not in adhesive contact with the electrode surface. Brief application of a modest dc current density adheres the arrays tightly to the surface. 相似文献
7.
Diminished proliferation of human immunodeficiency virus-specific CD4+ T cells is associated with diminished interleukin-2 (IL-2) production and is recovered by exogenous IL-2 总被引:11,自引:0,他引:11
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Iyasere C Tilton JC Johnson AJ Younes S Yassine-Diab B Sekaly RP Kwok WW Migueles SA Laborico AC Shupert WL Hallahan CW Davey RT Dybul M Vogel S Metcalf J Connors M 《Journal of virology》2003,77(20):10900-10909
Virus-specific CD4(+) T-cell function is thought to play a central role in induction and maintenance of effective CD8(+) T-cell responses in experimental animals or humans. However, the reasons that diminished proliferation of human immunodeficiency virus (HIV)-specific CD4(+) T cells is observed in the majority of infected patients and the role of these diminished responses in the loss of control of replication during the chronic phase of HIV infection remain incompletely understood. In a cohort of 15 patients that were selected for particularly strong HIV-specific CD4(+) T-cell responses, the effects of viremia on these responses were explored. Restriction of HIV replication was not observed during one to eight interruptions of antiretroviral therapy in the majority of patients (12 of 15). In each case, proliferative responses to HIV antigens were rapidly inhibited during viremia. The frequencies of cells that produce IFN-gamma in response to Gag, Pol, and Nef peptide pools were maintained during an interruption of therapy. In a subset of patients with elevated frequencies of interleukin-2 (IL-2)-producing cells, IL-2 production in response to HIV antigens was diminished during viremia. Addition of exogenous IL-2 was sufficient to rescue in vitro proliferation of DR0101 class II Gag or Pol tetramer(+) or total-Gag-specific CD4(+) T cells. These observations suggest that, during viremia, diminished in vitro proliferation of HIV-specific CD4(+) T cells is likely related to diminished IL-2 production. These results also suggest that relatively high frequencies of HIV-specific CD4(+) T cells persist in the peripheral blood during viremia, are not replicatively senescent, and proliferate when IL-2 is provided exogenously. 相似文献
8.
Flyvbjerg A Schrijvers BF De Vriese AS Tilton RG Rasch R 《American journal of physiology. Endocrinology and metabolism》2002,283(2):E362-E366
Various growth factors and cytokines have been implicated in different forms of kidney enlargement. Vascular endothelial growth factor (VEGF) is essential for normal renal development and plays a role in diabetic glomerular enlargement. To explore a possible role for VEGF in compensatory renal changes after uninephrectomy, we examined the effect of a neutralizing VEGF-antibody (VEGF-Ab) on glomerular volume and kidney weight in mice treated for 7 days. Serum and kidney insulin-like growth factor I (IGF-I) levels were measured, since IGF-I has been implicated in the pathogenesis of compensatory renal growth, and VEGF has been suggested to be a downstream mediator of IGF-I. Placebo-treated uninephrectomized mice displayed an early transient increase in kidney IGF-I concentration and an increase in glomerular volume and kidney weight. In VEGF-Ab-treated uninephrectomized animals, increased glomerular volume was abolished, whereas renal hypertrophy was partially blocked. Furthermore, the renal effects of VEGF-Ab administration were seen without affecting the renal IGF-I levels. In conclusion, these results demonstrate that compensatory glomerular growth after uninephrectomy is VEGF dependent. 相似文献
9.
Tilton SC Foran CM Benson WH 《Comparative biochemistry and physiology. Toxicology & pharmacology : CBP》2003,136(3):265-276
Cadmium (Cd) is a ubquitous element and a significant inorganic pollutant that has previously been found to bioaccumulate in reproductive organs of fish and disrupt important endocrine processes, especially those involved in synthesis, release and metabolism of hormones. Clearly, there is potential for reproductive effects in fish populations exposed to Cd, however, few studies have investigated the non-lethal consequences of Cd in fish. To this extent, adult male and female Japanese medaka were exposed to 0-10 ppb Cd for 7 weeks. Reproductive endpoints were monitored during weeks 6 and 7 of exposure and compared to physiological responses along the hypothalamus-pituitary-gonadal (HPG) axis, including plasma vitellogenin (VTG), hepatic estrogen receptor (ER), plasma steroids, gonadal-somatic indices (GSI), and gonadal steroid release. There were no observed effects on VTG and ER by long-term Cd exposure. However, gonadal steroid release was significantly decreased in males and females at all exposure concentrations and female plasma estradiol levels were significantly altered at concentrations higher than 5 ppb Cd. Overall, responses along the HPG axis were more sensitive to Cd exposure than the reproductive and developmental endpoints, which were not affected in this study, indicating that higher level impairment in fish might be relatively protected. 相似文献
10.
Balachandran C. Duraipandiyan V. Al-Dhabi N. A. Stalin A. Balakrishna K. Ignacimuthu S. Tilton F. 《Applied Biochemistry and Microbiology》2015,51(5):522-529
Applied Biochemistry and Microbiology - Anticancer activity of 9,10-anthraquinone isolated from soil-derived (Doddabetta forest, Nilgiris, Tamil Nadu, India) filamentous bacterium Streptomyces sp.... 相似文献