Rare earth magnets in orthodontics: an overview.
Magnets have been used in dentistry for many years. They can be made to push or pull teeth. The force they deliver can be directed, and they can exert their force through mucosa and bone, as well as within the mouth. In orthodontics they are used for intrusion of teeth, tooth movement along archwires, expansion, retention, in functional appliances, and in the treatment of impacted teeth. New 'high energy' magnets are capable of producing very high forces relative to their size. Although magnets are potentially very useful there are a number of problems that severely affect their performance; the force produced between any two magnets falls dramatically with distance, significant irreversible loss in force is seen if the magnets are heated and a dramatic reduction in force is seen if the magnets are not ideally aligned to one another. In addition, magnets corrode badly in the mouth and a robust coating is required to protect them. This paper outlines the background to high energy magnets used in orthodontics, discusses the relevant physical and biological properties of them, and reviews their applications. (+info)
Metal ion selectivity for formation of the calmodulin-metal-target peptide ternary complex studied by surface plasmon resonance spectroscopy.
Ion selectivities for Ca(2+) signaling pathways of 33 metal ions were examined based on the Ca(2+)-dependent on/off switching mechanism of calmodulin (CaM): Ca(2+) ion-induced selective binding of CaM-Ca(2+) ion complex to the target peptide was observed as an increase in surface plasmon resonance (SPR) signals. As the target peptide, M13 of 26-amino-acid residues derived from skeletal muscle myosin light-chain kinase was immobilized in the dextran matrix, over which sample solutions containing CaM and each metal ion were injected in a flow system. Large changes in SPR signals were also observed for Sr(2+), Ba(2+), Cd(2+), Pb(2+), Y(3+) and trivalent lanthanide ions, thereby indicating that not only Ca(2+) but also these metal ions induce the formation of CaM-M13-metal ion ternary complex. No SPR signal was, however, induced by Mg(2+), Co(2+), Ni(2+), Cu(2+), Zn(2+) and all monovalent metal ions examined. The latter silent SPR signal indicates that these ions, even if they bind to CaM, are incapable of forming the CaM-M13-metal ion ternary complex. Comparing the obtained SPR results with ionic radii of those metal ions, it was found that all cations examined with ionic radii close to or greater than that of Ca(2+) induced the formation of the CaM-metal-M13 ternary complex, whereas those with smaller ionic radii were not effective, or much less so. Since these results are so consistent with earlier systematic data for the effects of various metal ions on the conformational changes of CaM, it is concluded that the present SPR analysis may be used for a simple screening and evaluating method for physiologically relevant metal ion selectivity for the Ca(2+) signaling via CaM based on CaM/peptide interactions. (+info)
Calcium binding to the photosystem II subunit CP29.
We have identified a Ca(2+)-binding site of the 29-kDa chlorophyll a/b-binding protein CP29, a light harvesting protein of photosystem II most likely involved in photoregulation. (45)Ca(2+) binding studies and dot blot analyses of CP29 demonstrate that CP29 is a Ca(2+)-binding protein. The primary sequence of CP29 does not exhibit an obvious Ca(2+)-binding site therefore we have used Yb(3+) replacement to analyze this site. Near-infrared Yb(3+) vibronic side band fluorescence spectroscopy (Roselli, C., Boussac, A., and Mattioli, T. A. (1994) Proc. Natl. Acad. Sci. U. S. A. 91, 12897-12901) of Yb(3+)-reconstituted CP29 indicated a single population of Yb(3+)-binding sites rich in carboxylic acids, characteristic of Ca(2+)-binding sites. A structural model of CP29 presents two purported extra-membranar loops which are relatively rich in carboxylic acids, one on the stromae side and one on the lumenal side. The loop on the lumenal side is adjacent to glutamic acid 166 in helix C of CP29, which is known to be the binding site for dicyclohexylcarbodiimide (Pesaresi, P., Sandona, D., Giuffra, E. , and Bassi, R. (1997) FEBS Lett. 402, 151-156). Dicyclohexylcarbodiimide binding prevented Ca(2+) binding, therefore we propose that the Ca(2+) in CP29 is bound in the domain including the lumenal loop between helices B and C. (+info)
Activation of volume-regulated Cl(-) channels by ACh and ATP in Xenopus follicles.
Osmolarity-dependent ionic currents from follicle-enclosed Xenopus oocytes (follicles) were studied using electrophysiological techniques. Whole follicle currents were monitored using a two-electrode voltage clamp and single-channel activity was measured using the patch-clamp technique. In follicles held at -60 mV two chloride currents were activated in external hyposmotic solutions. One was the habitual volume-regulated current elicited by external hyposmolarity (ICl,swell), and the second was a slow and smooth current (Sin) generated by ACh or ATP application. In follicles, the permeability ratios for different anions with respect to Cl- were similar for both ICl,swell and Sin, with a sequence of: SCN- > I- > Br- >= NO3- >= Cl- > gluconate >= cyclamate > acetate > SO42-. Extracellular ATP blocked the outward component of Sin. Also, extracellular pH modulated the inactivation kinetics of Sin elicited by ACh; e.g. inactivation at +80 mV was approximately 100 % slower at pH 8.0 compared with that at pH 6.0. Lanthanides inhibited ICl, swell and Sin. La3+ completely inhibited ICl,swell with a half-maximal inhibitory concentration (IC50) of 17 +/- 1.9 microM, while Sin was blocked up to 55 % with an apparent IC50 of 36 +/- 2.6 microM. Patch-clamp recordings in follicular cells showed that hyposmotic challenge opened inward single-channel currents. The single channel conductance (4.7 +/- 0.4 pS) had a linear current-voltage relationship with a reversal membrane potential close to -20 mV. This single-channel activity was increased by application of ACh or ATP. The ICl,swell generation was not affected by pirenzepine or metoctramine, and did not affect the purinergic activation of the chloride current named Fin. Thus, ICl,swell was not generated via neurotransmitters released during cellular swelling. All together, equal discrimination for different anions, similar modulatory effects by extracellular pH, the blocking effects by ATP and La3+, and the same single-channel activity, strongly suggest that ICl,swell and Sin currents depend on the opening of the same type or a closely related class of volume-regulated chloride channels. (+info)
Trivalent ions activate abscisic acid-inducible promoters through an ABI1-dependent pathway in rice protoplasts.
The plant hormone abscisic acid (ABA) mediates many vital processes in plant growth and development, including seed dormancy, cell division, water use efficiency, and adaptation to drought, salinity, chilling, pathogen attack, and UV light. Our understanding of ABA signal transduction is fragmentary and would benefit from specific and facile probes of the process. Protoplasts from rice (Oryza sativa L. cv IR54) embryonic suspension cultures cotransformed with effector plasmids encoding the maize (Zea mays) VIVIPAROUS1 cDNA and/or the Arabidopsis dominant negative mutant (abi1-1) ABA-insensitive cDNA demonstrated genetic interactions of VIVIPAROUS1 and abi1-1 in transactivation of the ABA-inducible HVA1 promoter from barley (Hordeum vulgare), suggesting the mechanisms of these effectors are conserved among monocots and dicots. Trivalent ions have been shown to act as an effector of gene expression in plants and animals, although the mechanism of action is unknown. We show in two complementary transient ABA-inducible gene expression assays (beta-glucuronidase and luciferase enzymatic activities and quantitative flow cytometry of green fluorescent protein) that trivalent ions specifically interact with an ABI1-dependent ABA-signaling pathway leading to gene expression. Trivalent ions mimic ABA effects on gene expression and may be a useful tool to study ABA signaling. (+info)
Miniature single-particle immunoassay for prostate-specific antigen in serum using recombinant Fab fragments.
BACKGROUND: Quantitative, miniaturized nucleic acid assays and immunoassays can be developed with single microparticles, microfluorometric detection, and intrinsically fluorescent lanthanide chelates in a multiple assay format to decrease reagent consumption, cost, and assay time. We used recombinant Fab fragments to capture and detect free and total prostate-specific antigen (PSA) from serum in a submicroliter volume single-particle immunoassay. METHODS: Genetically engineered thiol-Fab or thiolated monoclonal antibodies (mAbs) were covalently attached onto uniformly sized 60-microm maleimide-activated microparticles. Free and total PSA were detected with europium- or terbium-labeled Fab fragments on a single microparticle using a microfluorometer in a time-resolved mode. RESULTS: The detection limit of the free- and total-PSA assays (mean + 3 SD of zero calibrator) was 0.35 microg/L, with a total volume of 330 nL per particle. An excellent correlation was found in microparticle and microtiter-well assays for 21 serum samples: slopes for free and total PSA were 1.06+/-0.03 and 1.03+/-0.02, respectively (S(y|x) = 0.084 and 0.057 microg/L), with intercepts of 0.013+/-0.018 and 0.013+/-0.017 microg/L (R>0.99). Furthermore, the particle-immobilized Fab fragment had a PSA binding capacity 1.5-fold higher than the intact mAb capacity on a single microparticle. Capacity, kinetics, and sensitivity of the Fab fragment and intact mAb assays in the microparticle and microtiter well formats are discussed. CONCLUSIONS: With site-specific (cysteine tail) covalent attachment of Fab fragments on a microparticle, subattomole amounts of PSA can be detected quantitatively. (+info)
Stable labeled microspheres to measure perfusion: validation of a neutron activation assay technique.
Neutron activation is an accurate analytic method in which trace quantities of isotopes of interest in a sample are activated and the emitted radiation is measured with high-resolution detection equipment. This study demonstrates the application of neutron activation for the measurement of myocardial perfusion using stable isotopically labeled microspheres. Stable labeled and standard radiolabeled microspheres (15 microm) were coinjected in an in vivo rabbit model of myocardial ischemia and reperfusion. Radiolabeled microspheres were detected with a standard gamma-well counter, and stable labeled microspheres were detected with a high-resolution Ge detection after neutron activation of the myocardial and reference blood samples. Regional myocardial blood flow was calculated from the deposition of radiolabeled and stable labeled microspheres. Both sets of microspheres gave similar measurements of regional myocardial blood flow over a wide range of flow with a high linear correlation (r = 0.95-0.99). Neutron activation is capable of detecting a single microsphere in an intact myocardial sample while providing simultaneous quantitative measurements of multiple isotope labels. This high sensitivity and capability for measuring perfusion in intact tissue are advantages over other techniques, such as optical detection of microspheres. Neutron activation also can provide an effective method for reducing the production of low-level radioactive waste generated from biomedical research. Further applications of neutron activation offer the potential for measuring other stable labeled compounds, such as fatty acids and growth factors, in conjunction with microsphere measured flow, providing the capability for simultaneous measurement of regional metabolism and perfusion. (+info)
Accessibility of tyrosine Y(.)(Z) to exogenous reductants and Mn(2+) in various Photosystem II preparations.
The reduction of tyrosine Y(.)(Z) by benzidine and exogenous Mn(2+) was studied by kinetic EPR experiments in various Photosystem II (PSII) preparations. Using lanthanide treated PSII membranes it was demonstrated that neither the extrinsic polypeptides (17, 23 and 33 kDa) nor the Mn complex block the accessibility of Y(.)(Z) to exogenous reductants, such as benzidine. In addition, it was shown that in the presence of the native Mn complex exogenous Mn(2+) does not reduce Y(.)(Z). (+info)