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排序方式: 共有192条查询结果,搜索用时 15 毫秒
1.
A. Magalhaes B. Maigret J. Hoflack J. N. F. Gomes H. A. Scheraga 《Journal of Protein Chemistry》1994,13(2):195-215
Although the majority of the ion pairs found in proteins consists of two charges of opposite sign, the observation of some unusual arrangements of two arginines led us to a search of such occurrences in the Brookhaven Protein Data Bank. We have found 41 Arginine-Arginine interactions with a C...C distance less than 5 å. Computer graphics analysis of these structures shows that most of the Arg-Arg pairs are found in the vicinity of the surface of the proteins, in an easily hydrated region. In order to determine which factors could stabilize such arrangements of species of similar charge, we have carried out AM1 semi-empirical calculations on a model of two guanidinium ions surrounded by several water molecules. The results show the existence of stable clusters with six or more water molecules, with distances between C atoms around 3 å. The bridging role of the water molecules is an important structural and energetic feature and we find bridges of two and three molecules between the guanidinium ions. These results are in good agreement with the structures found in our search of the experimental data. Enhancement of the electrostatic potential around these clusters, when compared to one of the guanidinium ions alone, is also demonstrated. 相似文献
2.
Differential response of cycling and noncycling cells to inducers of DNA synthesis and mitosis 总被引:1,自引:0,他引:1
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The objective of this study was to determine whether cells in G(0) phase are functionally distinct from those in G(1) with regard to their ability to respond to the inducers of DNA synthesis and to retard the cell cycle traverse of the G(2) component after fusion. Synchronized populations of HeLa cells in G(1) and human diploid fibroblasts in G(1) and G(0) phases were separately fused using UV-inactivated Sendai virus with HeLa cells prelabeled with [(3)H]ThdR and synchronized in S or G(2) phases. The kinetics of initiation of DNA synthesis in the nuclei of G(0) and G(1) cells residing in G(0)/S and G(1)/S dikaryons, respectively, were studied as a function of time after fusion. In the G(0)/G(2) and G(1)/G(2) fusions, the rate of entry into mitosis of the heterophasic binucleate cells was monitored in the presence of Colcemid. The effects of protein synthesis inhibition in the G(1) cells, and the UV irradiation of G(0) cells before fusion, on the rate of entry of the G(2) component into mitosis were also studied. The results of this study indicate that DNA synthesis can be induced in G(0)nuclei after fusion between G(0)- and S-phase cells, but G(0) nuclei are much slower than G(1) nuclei in responding to the inducers of DNA synthesis because the chromatin of G(0) cells is more condensed than it is in G(1) cells. A more interesting observation resulting from this study is that G(0) cells is more condensed than it is in G(1) cells. A more interesting observation resulting from this study is that G(0) cells differ from G(1) cells with regard to their effects on the cell cycle progression of the G(2) nucleus into mitosis. This difference between G(0) and G(1) cells appears to depend on certain factors, probably nonhistone proteins, present in G(1) cells but absent in G(0) cells. These factors can be induced in G(0) cells by UV irradiation and inhibited in G(1) cells by cycloheximide treatment. 相似文献
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4.
G.C. Micke T.M. Sullivan R.J. Soares Magalhaes P.J. Rolls S.T. Norman V.E.A. Perry 《Animal reproduction science》2010,117(1-2):1-10
Maternal nutrient intake during gestation can alter fetal growth. Whilst this has been studied extensively in the sheep, less is known about effects in the bovine. Composite-breed beef heifers were allocated to either a high (H/? = 76 MJ metabolisable energy (ME) and 1.4 kg crude protein (CP)) or low (L/? = 62 MJ ME and 0.4 kg CP daily) nutritional treatment at artificial insemination. Half of each nutritional group changed to an opposite nutritional group at the end of the first trimester (?/H = 82 MJ ME and 1.4 kg CP; ?/L = 62 MJ ME and 0.4 kg CP daily), resulting in 4 treatment groups: HH (n = 16); HL (n = 19); LH (n = 17); LL (n = 19). During the third trimester all heifers were fed the same diets. Fetuses were measured at 4-weekly intervals beginning at day 39 of gestation. Calves were also measured at birth for physical body variables. Low maternal nutrient intake was associated with decreased crown-rump length at day 39 (P < 0.01) and increased thoracic diameter at day 95 (P < 0.01). Umbilical cord diameter was reduced in L/? fetuses in the first trimester (P < 0.05) but was greater in ?/L fetuses in the second trimester compared to their respective H counterparts (P < 0.05). Calf birth weight was decreased in association with ?/L maternal diets (P < 0.05). In conclusion, fetal development of cattle may be affected by maternal nutrition as early as day 39 of gestation. This may be followed by either compensatory fetal growth, or alternatively, preferential fetal tissue growth that is dependant upon maternal nutrition. Clearly, calf birth weight may be altered by maternal nutrition during mid-gestation. 相似文献
5.
Physiological basis of reduced Al tolerance in ditelosomic lines of Chinese Spring wheat 总被引:13,自引:0,他引:13
Aluminum tolerance was assessed in the moderately Al-tolerant wheat (Triticum aestivum L.) cultivar Chinese Spring and a set of ditelosomic lines derived from Chinese Spring. Three ditelosomic lines lacking chromosome
arms 4DL, 5AS and 7AS, respectively, exhibited decreased Al tolerance relative to the euploid parent Chinese Spring based
on reduced root growth in Al-containing solutions. The physiological basis of the reduced Al tolerance was investigated. Measurements
by inductively coupled argon plasma mass spectroscopy of root apical Al accumulation demonstrated that two of these three
lines had a decreased ability to exclude Al from the root apex, the site of Al phytotoxicity. As Al-induced malate exudation
has been suggested to be an important physiological mechanism of Al tolerance in wheat, this parameter was quantified and
malate exudation was shown to be smaller in all three deletion lines compared with Chinese Spring. These results suggest that
the decreased Al tolerance in at least two of the three ditelosomic lines is due to the loss of different genes independently
influencing a single Al-tolerance mechanism, rather than to the loss of genes encoding alternative Al-tolerance mechanisms.
Received: 3 July 2000 / Accepted: 9 August 2000 相似文献
6.
Spada RG da Silva D Abdel-Hamid AZ Sobral-Hamaguchi SS Zuim NR Zanotti-Magalhaes EM Magalhaes LA Ribeiro-Paes JT 《Memórias do Instituto Oswaldo Cruz》2002,97(Z1):53-58
The analysis of the genetic variability related to susceptibility to Schistosoma mansoni infection in the vector of the genus Biomphalaria is important in terms of a better understanding of the epidemiology of schistosomiasis itself, the possible pathological implications of this interaction in vertebrate hosts, and the formulation of new strategies and approaches for disease control. In the present study, the genetic variability of B. glabrata strains found to be resistant or susceptible to S. mansoni infection was investigated using DNA amplification by random amplified polymorphic DNA-polymerase chain reaction (RAPD-PCR). The amplification products were analyzed on 8% polyacrylamide gel and stained with silver. We selected 10 primers, since they have previously been useful to detect polymorphism among B. glabrata and/or B. tenagophila. The results showed polymorphisms with 5 primers. Polymorphic bands observed only in the susceptible strain. The RAPD-PCR methodology represents an adequate approach for the analysis of genetic polymorphisms. The understanding of the genetic polymorphisms associated to resistance may contribute to the future identification of genomic sequences related to the resistance/susceptibility of Biomphalaria to the larval forms of S. mansoni and to the development of new strategies for the control of schistosomiasis. 相似文献
7.
Felicori LF Souza CT Velarde DT Magalhaes A Almeida AP Figueiredo S Richardson M Diniz CR Sanchez EF 《Protein expression and purification》2003,30(1):32-42
A kallikrein-like proteinase of Lachesis muta muta (bushmaster) venom, designated LV-Ka, was purified by gel filtration and anion exchange chromatographies. Physicochemical studies indicated that the purified enzyme is a 33 kDa monomeric glycoprotein, the Mr of which fell to 28 kDa after deglycosylation with PNGase F. Approximately 77% of the protein sequence was determined by sequencing the various fragments derived from digestions with endoproteases. The partial sequence obtained suggests that LV-Ka is of a similar size to other serine proteinases (i.e., approximately 234 amino acid residues). Sequence studies on the NH2-terminal region of the protein indicate that LV-Ka shares a high degree of sequence homology with the kallikrein-like enzymes EI and EII from Crotalus atrox, with crotalase from Crotalus adamanteus and significant homology with other serine proteinases from snake venoms and vertebrate serum enzymes. LV-Ka showed kallikrein-like activity, releasing bradikinin from kininogen as evidenced by guinea pig bioassay. In addition, intravenous injection of the proteinase (0.8 microg/g) was shown to lower blood pressure in experimental rats. In vitro, the isolated proteinase was shown to have neither fibrin(ogeno)lytic activity nor coagulant effect. LV-Ka was active upon the kallikrein substrates S-2266 and S-2302 (specific activity=13.0 and 31.5 U/mg, respectively; crude venom=0.25 and 6.0 U/mg) but had no proteolytic effect on dimethylcasein and insulin B chain. Its enzymatic activity was inhibited by NPGB and PMSF, indicating that the enzyme is a serine proteinase. Interestingly, one of the other reactions catalyzed by plasma kallikrein, the activation of plasminogen was one of the activities exhibited by LV-Ka. 相似文献
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9.
VLJ Whitehall TD Dumenil DM McKeone CE Bond ML Bettington RL Buttenshaw L Bowdler GW Montgomery LF Wockner BA Leggett 《Epigenetics》2014,9(11):1454-1460
The CpG Island Methylator Phenotype (CIMP) is fundamental to an important subset of colorectal cancer; however, its cause is unknown. CIMP is associated with microsatellite instability but is also found in BRAF mutant microsatellite stable cancers that are associated with poor prognosis. The isocitrate dehydrogenase 1 (IDH1) gene causes CIMP in glioma due to an activating mutation that produces the 2-hydroxyglutarate oncometabolite. We therefore examined IDH1 alteration as a potential cause of CIMP in colorectal cancer. The IDH1 mutational hotspot was screened in 86 CIMP-positive and 80 CIMP-negative cancers. The entire coding sequence was examined in 81 CIMP-positive colorectal cancers. Forty-seven cancers varying by CIMP-status and IDH1 mutation status were examined using Illumina 450K DNA methylation microarrays. The R132C IDH1 mutation was detected in 4/166 cancers. All IDH1 mutations were in CIMP cancers that were BRAF mutant and microsatellite stable (4/45, 8.9%). Unsupervised hierarchical cluster analysis identified an IDH1 mutation-like methylation signature in approximately half of the CIMP-positive cancers. IDH1 mutation appears to cause CIMP in a small proportion of BRAF mutant, microsatellite stable colorectal cancers. This study provides a precedent that a single gene mutation may cause CIMP in colorectal cancer, and that this will be associated with a specific epigenetic signature and clinicopathological features. 相似文献
10.