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941.
Kinetics of tributyrin hydrolysis by lipase 总被引:1,自引:0,他引:1
The kinetics for the tributyrin hydrolysis using lipase (Pseudomonas fluorscenes CCRC-17015) were investigated in the liquid–liquid and liquid–solid–liquid reaction systems in a batch reactor. The lipase was covalently immobilized onto the surface of porous polymethylacrylamide (PMAA) crosslinking with N,N-methylene biacrylamide with a spacer of ethylenediamine actived by glutaraldehyde. The conditions such as tributyrin concentration, temperature, agitation, and pH value, were evaluated to achieve the optimum reaction conditions for both free lipase and immobilized lipase. The kinetic parameters in the reaction system were also obtained for two reaction systems. The turnover numbers calculated for free lipase and immobilized lipase were 29 and 5.7 s−1, respectively. The parameters of k and km obtained using Lineweaver-Burk plot method were 26.2 mol/(mg min) and 1.35 mol/dm3 for free lipase, 5.2 mol/(mg min) and 0.2 mol/dm3 for immobilized lipase, respectively. The experimental results revealed good thermal stability, with greater stability at higher pH value for immobilized lipase in the liquid–solid–liquid reaction. 相似文献
942.
943.
Receptor protein tyrosine phosphatase alpha participates in the m1 muscarinic acetylcholine receptor-dependent regulation of Kv1.2 channel activity. 总被引:3,自引:0,他引:3 下载免费PDF全文
The phosphorylation state of a given tyrosine residue is determined by both protein tyrosine kinase (PTK) and protein tyrosine phosphatase (PTP) activities. However, little is known about the functional interaction of these opposing activities at the level of an identified effector molecule. G protein-coupled receptors (GPCRs), including the m1 muscarinic acetylcholine receptor (mAChR), regulate a tyrosine kinase activity that phosphorylates and suppresses current generated by the Kv1.2 potassium channel. We examined the possibility that PTPs also participate in this signaling pathway since the tyrosine phosphatase inhibitor vanadate increases the extent of both Kv1.2 phosphorylation and suppression. We show that an endogenous transmembrane tyrosine phosphatase, receptor tyrosine phosphatase alpha (RPTPalpha), becomes tyrosine phosphorylated and co-immunoprecipitates with Kv1.2 in a manner dependent on m1 receptor activation. The N- and C-termini of Kv1.2 are shown to bind RPTPalpha in vitro. Overexpression of RPTPalpha in Xenopus oocytes increases resting Kv1.2 current. Biochemical and electrophysiological analysis reveals that recruiting RPTPalpha to Kv1.2 functionally reverses the tyrosine kinase-induced phosphorylation and suppression of Kv1.2 current in mammalian cells. Taken together, these results identify RPTPalpha as a new target of m1 mAChR signaling and reveal a novel regulatory mechanism whereby GPCR-mediated suppression of a potassium channel depends on the coordinate and parallel regulation of PTK and PTP activities. 相似文献
944.
Yin-Yu Chang Heng-Li Huang Ya-Chi Chen Jui-Ting Hsu Tzong-Ming Shieh Ming-Tzu Tsai 《PloS one》2014,9(4)
Tantalum (Ta) is a promising metal for biomedical implants or implant coating for orthopedic and dental applications because of its excellent corrosion resistance, fracture toughness, and biocompatibility. This study synthesizes biocompatible tantalum carbide (TaC) and TaC/amorphous carbon (a-C) coatings with different carbon contents by using a twin-gun magnetron sputtering system to improve their biological properties and explore potential surgical implant or device applications. The carbon content in the deposited coatings was regulated by controlling the magnetron power ratio of the pure graphite and Ta cathodes. The deposited TaC and TaC/a-C coatings exhibited better cell viability of human osteosarcoma cell line MG-63 than the uncoated Ti and Ta-coated samples. Inverted optical and confocal imaging was used to demonstrate the cell adhesion, distribution, and proliferation of each sample at different time points during the whole culture period. The results show that the TaC/a-C coating, which contained two metastable phases (TaC and a-C), was more biocompatible with MG-63 cells compared to the pure Ta coating. This suggests that the TaC/a-C coatings exhibit a better biocompatible performance for MG-63 cells, and they may improve implant osseointegration in clinics. 相似文献
945.
Tzung-Ju Wu Yi-Hsuan Chiang Yi-Chien Lin Chang-Ru Tsai Tai-Yuan Yu Ming-Ta Sung Yan-Hwa Wu Lee Jing-Jer Lin 《The Journal of biological chemistry》2009,284(19):12801-12808
Ku is a heterodimeric protein involved in nonhomologous end-joining of the
DNA double-stranded break repair pathway. It binds to the double-stranded DNA
ends and then activates a series of repair enzymes that join the broken DNA.
In addition to its function in DNA repair, the yeast Saccharomyces
cerevisiae Ku (Yku) is also a component of telomere protein-DNA complexes
that affect telomere function. The yeast telomeres are composed of duplex
C1–3(A/T)G1–3 telomeric DNA repeats plus
single-stranded TG1–3 telomeric DNA tails. Here we show that
Yku is capable of binding to a tailed-duplex DNA formed by telomeric DNA that
mimics the structure of telomeres. Addition of Cdc13p, a single-stranded
telomeric DNA-binding protein, to the Yku-DNA complex enables the formation of
a ternary complex with Cdc13p binding to the single-stranded tail of the DNA
substrate. Because pre-loading of Cdc13p to the single-stranded telomeric tail
inhibits the binding of Yku, the results suggested that loading of Yku and
Cdc13p to telomeres is sequential. Through generating a double-stranded break
near telomeric DNA sequences, we found that Ku protein appears to bind to the
de novo synthesized telomeres earlier than that of Cdc13p in
vivo. Thus, our results indicated that Yku interacts directly with
telomeres and that sequential loading of Yku followed by Cdc13p to telomeres
is required for both proteins to form a ternary complex on telomeres. Our
results also offer a mechanism that the binding of Cdc13p to telomeres might
prevent Yku from initiating DNA double-stranded break repair pathway on
telomeres.DNA damages in the form of double-stranded breaks
(DSBs)4 compromise the
integrity of genomes. Failure in repairing or mis-repairing double-stranded
breaks can lead to chromosome instability and eventually cell death or cancer
(1). Double-stranded breaks are
repaired by two main pathways, the homologous recombination and nonhomologous
DNA end-joining. In nonhomologous DNA end-joining, Ku is the first protein to
bind to the DNA ends to initiate the repair pathway
(2). Upon binding, Ku then
recruits a series of repair enzymes to join the broken ends
(2). Ku is a heterodimeric
protein composed of 70- and ∼80-kDa subunits. In Saccharomyces
cerevisiae, Ku includes Yku70 and Yku80 subunits. Because the biochemical
configuration of the broken ends could be very diverse on DSBs, Ku binds to
double-stranded ends in a sequence- and energy-independent manner. It is
capable of binding to DNA ends with blunt 3′-overhangs or
5′-overhangs as well as double-stranded DNA with nicks, gaps, or
internal loops
(3–7).
However, Ku does not have high affinity to single-stranded DNA. The crystal
structure of human Ku heterodimer indicates that it forms a ring structure
that encircles duplex DNA (7).
This unique structure feature enables Ku to recognize DNA ends and achieves
its high affinity binding.In additional to the role in double-stranded break repair, Ku was shown to
be a component of telomeric protein-DNA complex in yeast and mammals
(8–10).
Telomeres are terminal structures of chromosomes composed of short tandem
repeated sequences (11,
12). Mutation of
YKU70 or YKU80 causes defects in telomere structure
(13–15),
telomere silencing
(16–19),
and replication timing of telomeres
(20). The function of yeast Ku
(Yku) on telomeres could mediate through protein-protein interaction with
Sir4p or protein-RNA interaction with Tlc1 RNA
(21,
22). For example, through the
interaction with Sir4p, Yku selectively affects telomeres silencing but not
the silent mating type loci
(17). Yku could also bind to
telomerase Tlc1 RNA for telomere length maintenance
(22). Judged by the DNA
binding activity of Yku, it is reasonable to suggest that it may bind directly
to telomeric DNA. Indeed, it was shown that human Ku is capable of binding
directly to telomeric DNA in vitro
(15). Moreover, because the
deletion of SIR4 in budding yeast
(23) or Taz1 in
fission yeast (24) does not
abolish the association of Ku with chromosomal ends, this suggests that Ku
might bind directly to telomeric DNA in cells. However, because yeast
telomeres have a short 12–14-mer single-stranded tail
(25), it is uncertain whether
Yku could pass the single-stranded region to reach its binding site. The
direct binding of Yku to telomeric DNA has not been experimentally
determined.In contrast to double-stranded breaks, the ends of linear chromosomes are
not recognized by repair enzymes as DNA damage. In S. cerevisiae,
Cdc13p is the single-stranded TG1–3 DNA-binding protein that
enables cells to differentiate whether the ends of a linear DNA are telomeres
or broken ends
(26–29).
Thus, although the mechanism of how cells prevent the activation of DSB repair
pathway in telomere is unclear, it is likely that binding of Cdc13p to
telomeres might inhibit the initiation of DNA damage response by the Ku
protein. Here, using a tailed-duplex DNA synthesized by telomeric DNA
sequences to mimic telomere structure, we showed that Yku binds directly to
this tailed-duplex DNA substrate and forms a ternary complex with Cdc13p. Our
results also showed that Yku loaded to a de novo synthesized telomere
earlier than Cdc13p in vivo. These results support the direct binding
of Yku to telomeric DNA and that the spatial orientation of Cdc13p might block
the activation of DSB repair pathway on telomeres. 相似文献
946.
Qubo Zhu Lingjun Meng Joseph K. Hsu Tao Lin Jun Teishima Robert Y.L. Tsai 《The Journal of cell biology》2009,185(5):827-839
Telomeric repeat binding factor 1 (TRF1) is a component of the multiprotein complex “shelterin,” which organizes the telomere into a high-order structure. TRF1 knockout embryos suffer from severe growth defects without apparent telomere dysfunction, suggesting an obligatory role for TRF1 in cell cycle control. To date, the mechanism regulating the mitotic increase in TRF1 protein expression and its function in mitosis remains unclear. Here, we identify guanine nucleotide-binding protein-like 3 (GNL3L), a GTP-binding protein most similar to nucleostemin, as a novel TRF1-interacting protein in vivo. GNL3L binds TRF1 in the nucleoplasm and is capable of promoting the homodimerization and telomeric association of TRF1, preventing promyelocytic leukemia body recruitment of telomere-bound TRF1, and stabilizing TRF1 protein by inhibiting its ubiquitylation and binding to FBX4, an E3 ubiquitin ligase for TRF1. Most importantly, the TRF1 protein-stabilizing activity of GNL3L mediates the mitotic increase of TRF1 protein and promotes the metaphase-to-anaphase transition. This work reveals novel aspects of TRF1 modulation by GNL3L. 相似文献
947.
Huang YH Shih CM Huang CJ Lin CM Chou CM Tsai ML Liu TP Chiu JF Chen CT 《Journal of cellular biochemistry》2006,98(3):577-589
Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disorder disease. Ten percent of the ALS patients are congenital (familial ALS), and the other 90% are sporadic ALS (SALS). It has been shown that mutations found in the Cu,Zn-SOD cause 20% of the familial ALS due to its low enzyme activity. We hypothesized that heavy metals may interfere the structure of Cu,Zn-SOD protein to suppress its activity in some of the SALS. In this study, we expressed and characterized the recombinant human Cu,Zn-SOD under various concentrations of Cu(2+), Zn(2+), and Cd(2+). By atomic absorption spectrophotometry, we demonstrated that adding of cadmium significantly increased the content of cadmium ion, but reduced its Zn(2+) content and enzyme activity of the Cu,Zn-SOD protein. The data of circular dichroism spectra demonstrated that the secondary structure of Cu,Zn-SOD/Cd is different from Cu,Zn-SOD, but close to apo-SOD. In addition to the effect of cadmium on Cu,Zn-SOD, cadmium was also shown to induce neural cell apoptosis. To further investigate the mechanism of neural cell apoptosis induced by cadmium, we used proteomics to analyze the altered protein expressions in neural cells treated with cadmium. The altered proteins include cellular structural proteins, stress-related and chaperone proteins, proteins involved in reactive oxygen species (ROS), enzyme proteins, and proteins that mediated cell death and survival signaling. Taken together, in this paper, we demonstrate that cadmium decreases the content of Zn(2+), changes the conformation of Cu,Zn-SOD protein to decrease its enzyme activity, and causes oxidative stress-induced neural cell apoptosis. 相似文献
948.
Mandal AK Zhang Z Kim SJ Tsai PC Mukherjee AB 《Journal of immunology (Baltimore, Md. : 1950)》2005,175(10):6271-6273
For many years, cyclooxygenase-2 (COX-2), a critical enzyme for PG production, has been the favorite target for anti-inflammatory drug development. However, recent revelations regarding the adverse effects of selective COX-2 inhibitors have stimulated intense debate. Interestingly, in the early phase of inflammation, COX-2 facilitates inflammatory PG production while in the late phase it has anti-inflammatory effects. Moreover, although some PGs are proinflammatory, others have anti-inflammatory effects. Thus, it is likely that PGs with opposing effects maintain homeostasis, although the molecular mechanism(s) remains unclear. We report here that an inflammatory PG, PGD2, via its receptor, mediates the activation of NF-kappaB stimulating COX-2 gene expression. Most interestingly, an anti-inflammatory PG (PGA1) suppresses NF-kappaB activation and inhibits COX-2 gene expression. We propose that while pro- and anti-inflammatory PGs counteract each other to maintain homeostasis, selective COX-2 inhibitors may disrupt this balance, thereby resulting in reported adverse effects. 相似文献
949.
950.
A eukaryotic catechol 1,2-dioxygenase (1,2-CTD) was produced from a Candida albicans TL3 that possesses high tolerance for phenol and strong phenol degrading activity. The 1,2-CTD was purified via ammonium
sulfate precipitation, Sephadex G-75 gel filtration, and HiTrap Q Sepharose column chromatography. The enzyme was purified
to homogeneity and found to be a homodimer with a subunit molecular weight of 32,000. Each subunit contained one iron. The
optimal temperature and pH were 25°C and 8.0, respectively. Substrate analysis showed that the purified enzyme was a type
I catechol 1,2-dioxygenase. This is the first time that a 1,2-CTD from a eukaryote (Candida albicans) has been characterized. Peptide sequencing on fragments of 1,2-CTD by Edman degradation and MALDI-TOF/TOF mass analyses
provided information of amino acid sequences for BLAST analysis, the outcome of the BLAST revealed that this eukaryotic 1,2-CTD
has high identity with a hypothetical protein, CaO19_12036, from Candida albicans SC5314. We conclude that the hypothetical protein is 1,2-CTD. 相似文献