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  • 1
    Electronic Resource
    Electronic Resource
    Epitaxial overgrowth of apatite crystals on the thin-ribbon precursor at early stages of porcine enamel mineralization (1993)
    Springer
    Calcified tissue international 53 (1993), S. 249-256 
    Details
    ISSN: 1432-0827
    Keywords: Enamel ; Amelogenesis ; Crystal growth ; Calcium phosphates ; Biomineralization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary The aim of the present work was to investigate changes in cross-sectional morphologies of enamel crystallites as a function of location in secretory porcine enamel. Enamel tissues were obtained from 5- to 6-month-old slaughtered piglets. For examination by electron microscopy, a portion of the secretory enamel was embedded in resin and ultrathin sections were prepared with a diamond knife. In parallel studies, compositional and structural changes of enamel mineral were assessed by chemical analysis and Fourier transform infrared (FTIR) spectroscopy. For this purpose, two consecutive layers of the outer secretory enamel, each approximately 30 μm thick, were separated from the labial side of permanent incisors. Using high-resolution electron microscopy, early events of enamel crystal growth were characterized as the epitaxial growth of small apatite units on the lateral surfaces of the initially precipitated thin ribbon. These apatite units had regular triangle or trapezoid cross-sections. After fusions of those isolated trapezoids on both lateral sides of the platy template, the resulting enamel crystallites had the well-documented flattened-hexagonal shapes in cross-sections. The initially precipitated thin plate was buried inside the overgrown apatite lamella and then retained as a central dark line. Similar morphological evidence for the epitaxial nucleation and overgrowth of carbonatoapatite on the platy template was obtainedin vitro. Chemical and FTIR analyses of the enamel layer samples showed that the characteristics of the youngest enamel mineral were distinct from those of enamel crystals found in older secretory enamel. The overall results support the concept that initial enamel mineralization comprises two events: the initial precipitation of thin ribbons and the subsequent epitaxial growth of apatite crystals on the two-dimensional octacalcium phosphate-like precursor.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01320910
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  • 2
    Electronic Resource
    Electronic Resource
    Common epitopes of mammalian amelogenins at the C-terminus and possible functional roles of the corresponding domain in enamel mineralization (1992)
    Springer
    Calcified tissue international 51 (1992), S. 85-91 
    Details
    ISSN: 1432-0827
    Keywords: Amelogenesis ; Pig, cow, rat, rabbit amelogenins ; Epitopes at the C-terminus ; Adsorption ; Enamel mineralization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary The present studies were undertaken to investigate the presence of common epitopes of mammalian amelogenins at the C-terminus and the possible functional importance of the conserved C-terminal domain in enamel mineralization during mammalian amelogenesis. Enamel proteins, including the intact amelogenins and their degraded polypeptides, were isolated from the secretory enamel of pig, cow, rat, and rabbit incisors. Rabbit and rat antipeptide sera, as well as rat anti-25 kD and 20 kD pig amelogenin sera, were used to identify the amelogenins among the isolated matrix proteins of each of the animal species. The antipeptide sera were developed previously (Aoba et al. [19]) using as immunogens the two synthetic peptides, C13 and C25, which correspond to the last 12 (plus Cys for KLH-conjugation) and 25 amino acid residues of pig intact amelogenin, respectively. Reactivity of the enamel proteins with each antiserum was examined by Western blot analysis. The results of immunoblotting showed that a few enamel matrix proteins in each of the mammalian species were recognized by the anti-C13 serum, specifically, pig amelogenin at 25 kD (and trace components at 27, 22, and 18 kD), cow amelogenin at 28 kD (trace components at 26, 22, 19, and 14 kD), rat amelogenins at 28 and 26 kD (and a trace component at 20 kD), and rabbit amelogenins at 24 and 21 kD (and a trace at 13 kD). The anti-C25 serum reacted additionally with pig amelogenin at 23 kD, cow amelogenin at 27 kD (a major matrix constituent), and rabbit protein at 19 kD. The anti-pig 20 kD amelogenin (lacking the last 25 amino acid residues at the C-terminus) serum reacted with a large number of pig, cow, and rat amelogenins but, interestingly, with none of the rabbit enamel proteins. Probing of rat enamel proteins with Maclura pomifera lectin showed the heterogeneity of glycosylation of rat amelogenins, particularly between the 28 and 26 kD intact amelogenins. In parallel adsorption studies, part of the enamel protein samples isolated from each of the species was used as adsorbates to investigate the selective adsorption of amelogenins onto hydroxyapatite. Immunoblot analysis of the proteins adsorbed onto the crystals revealed that the mammalian amelogenins having the common epitopes at the C-terminus, in general, adsorb preferentially onto hydroxyapatite. The adsorption affinity of the degraded amelogenins decreased significantly with the loss of reactivity toward the anti-C13 serum. The overall results support the contention that the intact mammalian amelogenins, including rat and rabbit amelogenins, share common epitopes at the C-terminus and that the conserved C-terminal domain plays an important role in setting the molecular structures of the intact amelogenins so as to facilitate the protein-enamel mineral interaction.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00296224
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  • 3
    Electronic Resource
    Electronic Resource
    Competitive adsorption of magnesium and calcium ions onto synthetic and biological apatites (1992)
    Springer
    Calcified tissue international 51 (1992), S. 143-150 
    Details
    ISSN: 1432-0827
    Keywords: Adsorption ; Magnesium ; Calcium ; Apatite crystals ; Enamel ; Dentin ; Bone
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary Magnesium (Mg) is a conspicuous constituent of hard tissues but its possible role in biomineralization is poorly understood. It is possible that Mg2+ adsorbed onto bioapatites may contribute to the modulation of crystal growth as such inhibitory activity has been reported for synthetic apatites. The present study was undertaken to determine the adsorption isotherms of Mg ions onto synthetic apatites and biominerals in tooth and bone tissues in the presence of other ions of natural occurrence. Synthetic crystals used as adsorbents were hydroxyapatite and, as a better prototype for the biomineral, Mg-containing carbonatoapatite. Human enamel and dentin materials were obtained from extracted, caries-free, permanent teeth. Porcine dentin materials at two developmental stages were obtained from erupted deciduous and unerupted permanent teeth of a 6-month-old slaughtered piglet. Porcine bone was obtained from the cortical portion of the mandible of the same animal. All biomineral samples were pulverized and then treated by plasma ashing (deproteination) at about 60°C. Each of the powdered samples was equilibrated in solutions containing various initial concentrations of Mg2+, Ca2+, and Na+ (or K+) as nitrate salts. Following equilibration, concentrations (and activities) of magnesium and calcium ions in the experimental solution were determined. The pH values of the equilibrium solutions were in the range of 6.2–6.5. Experimental data of the Mg adsorption onto hydroxyapatite were interpreted on the basis of a Langmuir-type model for binary systems assuming competition of Mg2+ and Ca2+ for the same adsorption sites on the crystal surfaces of the apatites. According to this model, the adsorbed Mg is expressed as a function of the ionic activity ratio (Mg2+)/(Ca2+) in the equilibrium solution. The model contains two parameters, the adsorption selectivity constant Ks and the maximum number of adsorption sites N (μmol/g). The numerical values of Ks were similar for all adsorbents used (synthetic and biological) and indicated the preferential adsorption of Ca2+ probably due to spacial restrictions extending to the very surface of the crystals. The initial level of Mg2+ in the surface pool was different in the various biominerals, probably reflecting the composition of fluid in which the biominerals were formed. Whereas the surface pool of Mg of human enamel was marginal, only 5% of the total Mg, significant fractions of the total Mg in human and porcine dentins (about 20–30%), and porcine bone (about 40%) existed on the crystal surfaces. There were significant differences in the total Mg and the value of the parameter N between young (unerupted) and mature (erupted) dentin minerals. It was ascertained that the occupancy of adsorption sites by Mg ions became greater with maturation of the dentin tissues. The overall results suggest that the Mg-mineral interaction in tooth and bone tissues may be a highly tissue-specific process, presumably reflecting differences in fluid composition (particularly Ca and Mg activities) responsible for biomineralization.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00298503
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  • 4
    Electronic Resource
    Electronic Resource
    Inhibition of apatite crystal growth by the amino-terminal segment of human salivary acidic proline-rich proteins (1984)
    Springer
    Calcified tissue international 36 (1984), S. 651-658 
    Details
    ISSN: 1432-0827
    Keywords: Salivary proteins ; Hydroxyapatite ; Adsorption ; Precipitation-inhibitor ; Phosphoserine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary Inhibition of seeded apatitic crystal growth by human salivary acidic proline-rich phosphoproteins (PRP) has been related to their adsorption onto the apatite seeds. The amino-terminal 30-residue segment of the PRP makes an important contribution to this adsorption. This peptide (PRP1(T1)) and its dephosphorylated analogue from PRP3 (PRP3(T1)DP) were prepared. They have identical sequences, except the phosphates at residues 8 and 22 in PRP1(T1) are absent from PRP3(T1)DP. Adsorption of these peptides onto hydroxyapatite and their effect on crystal growth from a defined supersaturated solution was studied. Adsorption behavior was adequately described by the Langmuir adsorption isotherm. The adsorption affinity constant of PRP1(T1) (K=20,200 ml/µmol) was more than 10 times the corresponding value for PRP3(T1)DP (1,800 ml/µmol), and similar to that of the parent protein, PRP1 (26,200 ml/µmol). Inhibition of crystal growth by the peptides was interpreted in terms of the fractional coverage of the maximum number of adsorption sites (as derived from the adsorption isotherms), suggesting that the molecules block, by adsorption, specific growth sites on these surfaces. Comparison of precipitation kinetics showed that PRP1(T1) is a more effective inhibitor than PRP3(T1)DP at the same initial concentration (10−6−10−7 M). However, on the basis of per mol adsorbed, PRP3(T1)DP displays a greater inhibitory activity; such a behavior is consistent with a more open molecular structure which blocks more growth sites per mol adsorbed than PRP1(T1). Because of its high affinity constant, preadsorbed PRP1(T1) remains in the condensed state in the supersaturated solution used, whereas the preadsorbed PRP3(T1)DP molecules desorb to some extent, resulting in a decrease in inhibitory activity. The results show that the amino-terminal segment of the PRP and the two phosphoserine residues present in this segment are particularly important in the function proposed for these proteins in the oral environment.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02405385
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    Paper (German National Licenses)
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