The present study examined the mechanism for caries resistance and the pulp responses in vital teeth following the use of the augmented-pressure adhesive displacement technique. Dentin adhesives were ...applied to the surface of sound dentin disks in 4 experimental groups: non-antibacterial adhesive and gentle adhesive displacement (N-G), non-antibacterial adhesive and augmented-pressure adhesive displacement (N-H), antibacterial adhesive and gentle adhesive displacement (A-G), antibacterial adhesive and augmented-pressure adhesive displacement (A-H). The depth of demineralization induced by biological or chemical demineralization models was measured using confocal laser scanning microscopy and analyzed with two-way ANOVA. Pulp responses of vital dog's teeth to the augmented-pressure adhesive displacement technique were evaluated using light microscopy. Depth of demineralization was significantly affected by "adhesive type" and "intensity of adhesive displacement" for biological demineralization. For chemical demineralization, only "intensity of adhesive displacement" showed significant influence on lesion depth. Pulp response of 0.1, 0.2 and 0.3 MPa groups showed only moderate disorganization of the odontoblast layer at 24 hours that completely re-organized after 3 weeks. Augmented-pressure adhesive displacement improves the caries resistance property of bonded dentin and does not cause irreversible pulpal damage to vital teeth when the air pressure employed is equal or smaller than 0.3 MPa.
Fluorination-assisted electrothermal vaporization (ETV)-inductively coupled plasma-atomic emission spectrometry (ICP-AES) for the direct determination of trace amounts of refractory impurity elements ...in silicon carbide ceramic powders using slurry sampling has been developed. Investigation indicated that a polytetrafluoroethylene (PTFE) emulsion is a useful fluorinating reagent for the destruction of silicon carbide and simultaneous vaporization of the refractory impurities like B, Mo, Ti, and Zr. The vaporization behaviors of the analytes in slurry and solution were comparatively investigated in the presence of PTFE. The fluorinating vaporization processes and the influence factors for this method have been also studied in detail. The experimental results indicated that 80
μg silicon carbide (10
μl of 0.8% (m/v) slurry) could be destroyed and vaporized completely with 600
μg of PTFE under the selected conditions. Calibration was performed using the standard addition method with aqueous standard solutions. The accuracy was checked by comparison of the results with those obtained by solution fluorination-assisted ETV-ICP-AES and pneumatic nebulization (PN)-ICP-AES involving a wet-chemical decomposition of the sample. Detection limits between 0.5
μg
g
−1 (B) and 0.2
μg
g
−1 (Mo) were achieved. In most cases, the precision expressed as relative standard deviation (R.S.D.) was better than 8%.
Guanine deaminase, a key enzyme in the nucleotide metabolism, catalyzes the hydrolytic deamination of guanine into xanthine.
The crystal structure of the 156-residue guanine deaminase from Bacillus ...subtilis has been solved at 1.17-Ã resolution. Unexpectedly, the C-terminal segment is swapped to form an intersubunit active site
and an intertwined dimer with an extensive interface of 3900 Ã 2 per monomer. The essential zinc ion is ligated by a water molecule together with His 53 , Cys 83 , and Cys 86 . A transition state analog was modeled into the active site cavity based on the tightly bound imidazole and water molecules,
allowing identification of the conserved deamination mechanism and specific substrate recognition by Asp 114 and Tyr 156â² . The closed conformation also reveals that substrate binding seals the active site entrance, which is controlled by the C-terminal
tail. Therefore, the domain swapping has not only facilitated the dimerization but has also ensured specific substrate recognition.
Finally, a detailed structural comparison of the cytidine deaminase superfamily illustrates the functional versatility of
the divergent active sites found in the guanine, cytosine, and cytidine deaminases and suggests putative specific substrate-interacting
residues for other members such as dCMP deaminases.
Palladium nanoparticles (PdNPs) were successfully attached and grown on an indium tin oxide (ITO) surface using a seed-mediated growth method, i.e., via a simple two-step immersion of the ITO ...substrate into the seed and growth solutions. After the growth treatment for 24 h, PdNPs grew up to 60−80 nm, exhibiting crystal-like appearances and accompanying the formation of short rodlike nanocrystals as a minor product. Thus prepared PdNPs tend to stick each other, so that the dense gathering of PdNPs was observed on the ITO surfaces. Due to the dense attachment, the PdNPs directly attached to the ITO (PdNP/ITO) electrode had a significantly lowered charge-transfer resistivity compared with that of a bare ITO, and the redox reaction of Fe(CN)63-/Fe(CN)64- was observed as reversible in 0.1 M phosphate buffer solution. The electrocatalytic property of PdNPs was confirmed for the reduction of oxygen. In addition, some typical responses were observed in 0.5 M H2SO4 with the PdNP/ITO electrode, reflecting both the characteristics of NPs and the thin layer in nanoscale. The present preparation method of PdNP-attached surfaces would be promising for catalytic applications as well as electrochemical uses.
Human mitochondrial malic enzyme is a regulatory enzyme with ATP as an inhibitor. Structural studies reveal that the enzyme has two ATP-binding sites, one at the NAD+-binding site in the active ...center and the other at the exo site in the tetramer interface. Inhibition of the enzyme activity is due to the competition between ATP and NAD+ for the nucleotide-binding site at the active center with an inhibition constant of 81 μM. Binding of the ATP molecule at the exo site, on the other hand, is important for the maintenance of the quaternary structural integrity. The enzyme exists in solution at neutral pH and at equilibrium of the dimer and tetramer with a dissociation constant (K TD) of 0.67 μM. ATP, at a physiological concentration, shifts the equilibrium toward tetramer and decreases the K TD by many orders of magnitude. Mutation of a single residue Arg542 at the tetrameric interfacial exo site resulted in dimeric mutants. ATP thus has dual functional roles in the mitochondrial malic enzyme.
Malic enzyme is a tetrameric protein with double dimer quaternary structure. In 3–5
M urea, the pigeon cytosolic NADP
+-dependent malic enzyme unfolded and aggregated into various forms with dimers ...as the basic unit. Under the same denaturing conditions but in the presence of 4
mM Mn
2+, the enzyme existed exclusively as a molten globule dimer in solution. Similar to pigeon enzyme (Chang, G. G., T. M. Huang, and T. C. Chang. 1988.
Biochem. J. 254:123–130), the human mitochondrial NAD
+-dependent malic enzyme also underwent a reversible tetramer-dimer-monomer quaternary structural change in an acidic pH environment, which resulted in a molten globule state that is also prone to aggregate. The aggregation of pigeon enzyme was attributable to Trp-572 side chain. Mutation of Trp-572 to Phe, His, Ile, Ser, or Ala abolished the protective effect of the metal ions. The cytosolic malic enzyme was completely digested within 2
h by trypsin. In the presence of Mn
2+, a specific cutting site in the Lys-352-Gly-Arg-354 region was able to generate a unique polypeptide with
M
r of 37
kDa, and this polypeptide was resistant to further digestion. These results indicate that, during the catalytic process of malic enzyme, binding metal ion induces a conformational change within the enzyme from the open form to an intermediate form, which upon binding of L-malate, transforms further into a catalytically competent closed form.
Caffeic acid phenylether ester (CAPE) has potent antioxidant, anti-inflammatory, antiviral, anti-proliferative, immunomodulatory and pro-apoptotic activities. The activities of CAPE and its novel ...synthetic derivatives, caffeic acid octyl ester (CAO) and 1-octyl caffeamide (CAN-8), were investigated in this study.
Cultured human cells were incubated with or without these compounds. The effect of these compounds on cell apoptosis, intracellular level of hydrogen peroxide and mitochondrial potential were analyzed. Western blot analysis was used to study the effect of alterations in protein level of caspases, Bcl-2 family, p21, p53 and c-Jun upon drug treatment.
These compounds arrested cell proliferation, triggered cell apoptosis and caused a marked scavenging effect of hydrogen peroxide. Apoptosis induced by CAPE or CAO is associated with increased expression of p53, p21 and c-Jun. While the levels of Bcl-2 and Bcl-xL were relatively unchanged, these compounds induced a marked reduction in Mcl-1 level. The CAPE- or CAO-induced apoptosis was also accompanied by a rapid loss of mitochondrial transmembrane potential and activation of caspase-3 and caspase-8, suggesting a mitochondrial-dependent mechanism. In causing these cellular actions, CAO was shown to be comparable or more potent than CAPE, whereas the amide analogue CAN-8 displayed much weaker activities than both CAPE and CAO. Since these three compounds contain similar antioxidant functionality, the difference in their potency suggests that the octyl moiety in CAO is an important determinant for the enhanced activities.
We have characterized a novel CAPE structure analogue, CAO, which showed strong antioxidant and proapoptotic activities. In addition, we demonstrated that down-regulation of Mcl-1 gene expression and activation of caspase-8 are associated with CAPE-triggered cell apoptosis.
A new electrochemical assaying approach with label-free to identify GG mismatch in DNA duplexes was developed by applying a new double functional probe (FecNC), ferrocenyl modified naphthyridine ...derivative, which contain recognition domain (naphthyridine derivative) and electroactive center (ferrocenyl group). The double functional probe exhibited not only the excellent electrochemical response devoted from ferrocenyl but also high selective electrochemical signal “off” for G–G mismatch duplex. The interaction was also verified by melting temperature and circular dichroismic spectra (CD). The electrochemical investigation showed that the redox of FecNC was a diffusion-controlled process and the diffusion coefficient of bound-FecNC was much smaller than free FecNC. The correlation between the current of FecNC and concentration of GG mismatch duplex indicated that the bind saturation point was about at a 1:1 mole ratio. The novel double functional electrochemical probe might provide a versatile and low-cost way to detect single nucleotide polymorphisms, which could be found extensive applications in the diagnosis of the genetic diseases.
► Double functional probe (FecNC) containing recognition and electrochemical activity domains was achieved by conjugated ferrocenyl with naphthyridine derivatives. ► Through the designed double functional probe (FecNC), a novel label-free electrochemical approach was developed for high selective recognition of GG mismatch. ► Presence of ct-DNA did not interfere with recognition ability of FecNC for GG mismatch, which contributed to real SNP detection. ► Label-free electrochemical approach has very simple experimental operation only with a naked Au electrode, without immobilizing and introducing additional reporter molecule.
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