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排序方式: 共有726条查询结果,搜索用时 11 毫秒
1.
Enzymatic desulfurization of dibenzothiophene by a cell-free system of Rhodococcus erythropolis D-1 总被引:1,自引:0,他引:1
Abstract Pseudomonas syringae cells were exposed to Cu2+ alone or in the precence of acetate, proline or cysteine, at concentrations that reduced free Cu2+ to 1/10 of the total copper. Ligand concentrations (designated as isoeffective) were determined experimentally using a Cu2+ -selective electrode and confirmed by computer calculations using published stability constants. Exposure of P. syringae cells to Cu2+ alone resulted in rapid and pronounced cell death, and binding of most of the copper in solution. The addition of acetate, proline or cysteine, a few minutes after Cu2+ treatment, resulted in a significant reduction in cell death, and in the amount of copper bound to the cells. For short exposures to Cu2+ , cysteine was more effective than acetate or proline, but after 60 min of treatment, similar results were observed with these ligands. The addition of ligands before Cu2+ resulted in even more reduced copper toxicity. The results showed that, at isoeffective concentrations, weak and moderate copper-ligands can effectively antagonize copper toxicity, and that this protective effect does not require previously equilibrated copper-ligand solutions and is not very dependent of the nature of the ligand. 相似文献
2.
Ribonuclease P (RNase P) is a ribonucleoprotein complex involved in the processing of the 5′-leader sequence of precursor tRNA. Human RNase P protein subunits Rpp21 and Rpp29, which bind to each other, with catalytic RNA (H1 RNA) are sufficient for activating endonucleolytic cleavage of precursor tRNA. Here we have determined the crystal structure of the complex between the Pyrococcus horikoshii RNase P proteins PhoRpp21 and PhoRpp29, the archaeal homologs of Rpp21 and Rpp29, respectively. PhoRpp21 and PhoRpp29 form a heterodimeric structure where the two N-terminal helices (α1 and α2) in PhoRpp21 predominantly interact with the N-terminal extended structure, the β-strand (β2), and the C-terminal helix (α3) in PhoRpp29. The interface is dominated by hydrogen bonds and several salt bridges, rather than hydrophobic interactions. The electrostatic potential on the surface of the heterodimer shows a positively charged cluster on one face, suggesting a possible RNA-binding surface of the PhoRpp21-PhoRpp29 complex. The present structure, along with the result of a mutational analysis, suggests that heterodimerization between PhoRpp21 and PhoRpp29 plays an important role in the function of P. horikoshii RNase P. 相似文献
3.
Size advantage for male function and size‐dependent sex allocation in Ambrosia artemisiifolia,a wind‐pollinated plant 下载免费PDF全文
In wind‐pollinated plants, male‐biased sex allocation is often positively associated with plant size and height. However, effects of size (biomass or reproductive investment) and height were not separated in most previous studies. Here, using experimental populations of monoecious plants, Ambrosia altemisiifolia, we examined (1) how male and female reproductive investments (MRI and FRI) change with biomass and height, (2) how MRI and height affect male reproductive success (MRS) and pollen dispersal, and (3) how height affects seed production. Pollen dispersal kernel and selection gradients on MRS were estimated by 2,102 seeds using six microsatellite markers. First, MRI increased with height, but FRI did not, suggesting that sex allocation is more male‐biased with increasing plant height. On the other hand, both MRI and FRI increased with biomass but often more greatly for FRI, and consequently, sex allocation was often female‐biased with biomass. Second, MRS increased with both height and MRI, the latter having the same or larger effect on MRS. Estimated pollen dispersal kernel was fat‐tailed, with the maximum distance between mates tending to increase with MRI but not with height. Third, the number of seeds did not increase with height. Those findings showed that the male‐biased sex allocation in taller plants of A. artemisiifolia is explained by a direct effect of height on MRS. 相似文献
4.
5.
Y Fujishima N Maeda K Inoue S Kashine H Nishizawa A Hirata J Kozawa T Yasuda K Okita A Imagawa T Funahashi I Shimomura 《Cardiovascular diabetology》2012,11(1):107-8
ABSTRACT: BACKGROUND: We recently reported that short-term treatment with liraglutide (20.0 +/- 6.4 days) reduced body weight and improved some scales of eating behavior in Japanese type 2 diabetes inpatients. However, it remained uncertain whether such liraglutide-induced improvement is maintained after discharge from the hospital. The aim of the present study was to determine the long-term effects of liraglutide on body weight, glycemic control, and eating behavior in Japanese obese type 2 diabetics. METHODS: Patients with obesity (body mass index (BMI) >25 kg/m2) and type 2 diabetes were hospitalized at Osaka University Hospital between November 2010 and December 2011. BMI and glycated hemoglobin (HbA1c) were examined on admission, at discharge and at 1, 3, and 6 months after discharge. For the liraglutide group (BMI; 31.3 +/- 5.3 kg/m2, n = 29), patients were introduced to liraglutide after correction of hyperglycemic by insulin or oral glucose-lowering drugs and maintained on liraglutide after discharge. Eating behavior was assessed in patients treated with liraglutide using The Guideline For Obesity questionnaire issued by the Japan Society for the Study of Obesity, at admission, discharge, 3 and 6 months after discharge. For the insulin group (BMI; 29.1 +/- 3.0 kg/m2, n = 28), each patient was treated with insulin during hospitalization and glycemic control maintained by insulin after discharge. RESULTS: Liraglutide induced significant and persistent weight loss from admission up to 6 months after discharge, while no change in body weight after discharge was noted in the insulin group. Liraglutide produced significant improvements in all major scores of eating behavior questionnaire items and such effect was maintained at 6 months after discharge. Weight loss correlated significantly with the decrease in scores for recognition of weight and constitution, sense of hunger, and eating style. CONCLUSION: Liraglutide produced meaningful long-term weight loss and significantly improved eating behavior in obese Japanese patients with type 2 diabetes. 相似文献
6.
Hayashi Y Okino N Kakuta Y Shikanai T Tani M Narimatsu H Ito M 《The Journal of biological chemistry》2007,282(42):30889-30900
Using C6-NBD-glucosylceramide (GlcCer) as a substrate, we detected the activity of a conduritol B epoxide-insensitive neutral glycosylceramidase in cytosolic fractions of zebrafish embryos, mouse and rat brains, and human fibroblasts. The candidates for the enzyme were assigned to the Klotho (KL), whose family members share a beta-glucosidase-like domain but whose natural substrates are unknown. Among this family, only the KL-related protein (KLrP) is capable of degrading C6-NBD-GlcCer when expressed in CHOP cells, in which Myc-tagged KLrP was exclusively distributed in the cytosol. In addition, knockdown of the endogenous KLrP by small interfering RNA increased the cellular level of GlcCer. The purified recombinant KLrP hydrolyzed 4-methylumbelliferyl-glucose, C6-NBD-GlcCer, and authentic GlcCer at pH 6.0. The enzyme also hydrolyzed the corresponding galactosyl derivatives, but each k(cat)/Km was much lower than that for glucosyl derivatives. The x-ray structure of KLrP at 1.6A resolution revealed that KLrP is a (beta/alpha)8 TIM barrel, in which Glu(165) and Glu(373) at the carboxyl termini of beta-strands 4 and 7 could function as an acid/base catalyst and nucleophile, respectively. The substrate-binding cleft of the enzyme was occupied with palmitic acid and oleic acid when the recombinant protein was crystallized in a complex with glucose. GlcCer was found to fit well the cleft of the crystal structure of KLrP. Collectively, KLrP was identified as a cytosolic neutral glycosylceramidase that could be involved in a novel nonlysosomal catabolic pathway of GlcCer. 相似文献
7.
The phenylboronic acids substituted with an azo group on the ortho-position show a significant change in UV-vis spectra upon sugar binding. A new mechanism for the spectral change of the dyes is proposed based on the formation and cleavage of B-N dative bond between boronic acid group and azo group. 相似文献
8.
The adaptation to alternate host plants of introduced herbivorous insects can be vital to agriculture due to the emergence of crop pests. Historically, it is assumed that there are trade-offs associated with the adaptation to new host plants; a generalist genotype that adapts to an alternate host is expected to have a relatively lower fitness on the ancestral host than a specialist genotype (physiological cost) or a relatively lower host-searching ability for the ancestral host plant (behavioral cost). In this study, we tested the costs of adaptation to a new host plant in the introduced herbivorous insect, Ophraella communa LeSage (Coleoptera: Chrysomelidae). In its native range (United States), O. communa feeds mostly on Ambrosia artemisiifolia L. (Asterales: Asteraceae) and cannot utilize the related species, Ambrosia trifida L. (Asterales: Asteraceae), as a host plant. On the other hand, the introduced O. communa population in Japan utilizes A. trifida extensively, and is adapting to it, both physiologically and behaviorally. We compared larval performance on the ancestral and alternate plants and adult host-searching ability between the native and introduced beetle populations. The introduced O. communa showed higher larval survival and adult feeding preference for the alternate host plant A. trifida than did the native O. communa, indicating that the introduced O. communa has rapidly adapted to the alternate host plant. However, there are no differences in either larval performance on the ancestral host A. artemisiifolia or host-searching accuracy between the native and introduced O. communa. 相似文献
9.
Tomoya Isaji Yuya Sato Tomohiko Fukuda Jianguo Gu 《The Journal of biological chemistry》2009,284(18):12207-12216
N-Glycosylation of integrin α5β1 plays a crucial role
in cell spreading, cell migration, ligand binding, and dimer formation, but
the detailed mechanisms by which N-glycosylation mediates these
functions remain unclear. In a previous study, we showed that three potential
N-glycosylation sites (α5S3–5) on the β-propeller of
the α5 subunit are essential to the functional expression of the
subunit. In particular, site 5 (α5S5) is the most important for its
expression on the cell surface. In this study, the function of the
N-glycans on the integrin β1 subunit was investigated using
sequential site-directed mutagenesis to remove the combined putative
N-glycosylation sites. Removal of the N-glycosylation sites
on the I-like domain of the β1 subunit (i.e. the Δ4-6
mutant) decreased both the level of expression and heterodimeric formation,
resulting in inhibition of cell spreading. Interestingly, cell spreading was
observed only when the β1 subunit possessed these three
N-glycosylation sites (i.e. the S4-6 mutant). Furthermore,
the S4-6 mutant could form heterodimers with either α5S3-5 or α5S5
mutant of the α5 subunit. Taken together, the results of the present
study reveal for the first time that N-glycosylation of the I-like
domain of the β1 subunit is essential to both the heterodimer formation
and biological function of the subunit. Moreover, because the
α5S3-5/β1S4-6 mutant represents the minimal
N-glycosylation required for functional expression of the β1
subunit, it might also be useful for the study of molecular structures.Integrin is a heterodimeric glycoprotein that consists of both an α
and a β subunit (1). The
interaction between integrin and the extracellular matrix is essential to both
physiologic and pathologic events, such as cell migration, development, cell
viability, immune homeostasis, and tumorigenesis
(2,
3). Among the integrin
superfamily, β1 integrin can combine with 12 distinct α subunits
(α1–11, αv) to form heterodimers, thereby acquiring a wide
variety of ligand specificity
(1,
4). Integrins are thought to be
regulated by inside-out signaling mechanisms that provoke conformational
changes, which modulate the affinity of integrin for the ligand
(5). However, an increasing
body of evidence suggests that cell-surface carbohydrates mediate a variety of
interactions between integrin and its extracellular environment, thereby
affecting integrin activity and possibly tumor metastasis as well
(6–8).Guo et al. (9)
reported that an increase in β1–6-GlcNAc sugar chains on the
integrin β1 subunit stimulated cell migration. In addition, elevated
sialylation of the β1 subunit, because of Ras-induced STGal-I transferase
activity, also induced cell migration
(10,
11). Conversely, cell
migration and spreading were reduced by the addition of a bisecting GlcNAc,
which is a product of N-acetylglucosaminyltransferase III
(GnT-III),2 to the
α5β1 and α3β1 integrins
(12,
13). Alterations of
N-glycans on integrins might also regulate their cis interactions
with membrane-associated proteins, including the epidermal growth factor
receptor, the galectin family, and the tetraspanin family of proteins
(14–19).In addition to the positive and negative regulatory effects of
N-glycan, several research groups have reported that
N-glycans must be present on integrin α5β1 for the
αβ heterodimer formation and proper integrin-matrix interactions.
Consistent with this hypothesis, in the presence of the glycosylation
inhibitor, tunicamycin, normal integrin-substrate binding and transport to the
cell surface are inhibited
(20). Moreover, treatment of
purified integrin with N-glycosidase F blocked both the inherent
association of the subunits and the interaction between integrin and
fibronectin (FN) (21). These
results suggest that N-glycosylation is essential to the functional
expression of α5β1. However, because integrin α5β1
contains 26 potential N-linked glycosylation sites, 14 in the α
subunit and 12 in the β subunit, identification of the sites that are
essential to its biological functions is key to understanding the molecular
mechanisms by which N-glycans alter integrin function. Recently, our
group determined that N-glycosylation of the β-propeller domain
on the α5 subunit is essential to both heterodimerization and biological
functions of the subunit. Furthermore, we determined that sites 3–5 are
the most important sites for α5 subunit-mediated cell spreading and
migration on FN (22). The
purpose of this study was to clarify the roles of N-glycosylation of
the β1 subunit. Therefore, we performed combined substitutions in the
putative N-glycosylation sites by replacement of asparagine residues
with glutamine residues. We subsequently introduced these mutated genes into
β1-deficient epithelial cells (GE11). The results of these mutation
experiments revealed that the N-glycosylation sites on the I-like
domain of the β1 subunit, sites number 4–6 (S4-6), are essential to
both heterodimer formation and biological functions, such as cell
spreading. 相似文献
10.
Kagami A Sakuno T Yamagishi Y Ishiguro T Tsukahara T Shirahige K Tanaka K Watanabe Y 《EMBO reports》2011,12(11):1189-1195
In fission yeast, meiotic mono-orientation of sister kinetochores is established by cohesion at the core centromere, which is established by a meiotic cohesin complex and the kinetochore protein Moa1. The cohesin subunit Psm3 is acetylated by Eso1 and deacetylated by Clr6. We show that in meiosis, Eso1 is required for establishing core centromere cohesion during S phase, whereas Moa1 is required for maintaining this cohesion after S phase. The clr6-1 mutation suppresses the mono-orientation defect of moa1Δ cells, although the Clr6 target for this suppression is not Psm3. Thus, several acetylations are crucial for establishing and maintaining core centromere cohesion. 相似文献