PubMed Health⌕ Search

Biomedical subjects

E C Moreno

Publications and source records attributed to E C Moreno.

At least 73 records · Page 4Linked to original sources
PubMed1983

Concentration-dependent multiple binding sites on saliva-treated hydroxyapatite for Streptococcus sanguis.

The influence of bacterial cell concentration on estimates of the number of binding sites and the affinity for the adsorption of a strain of Streptococcus sanguis to saliva-treated hydroxyapatite was determined, and the possible presence of multiple binding sites for this organism was tested. The range of concentrations of available bacteria varied from 4.7 x 10(6) to 5,960 x 10(6) cells per ml. The numbers of adsorbed bacteria increased over the entire range tested, but a suggestion of a break in an otherwise smooth adsorption isotherm was evident. Values for the number of binding sites and the affinity varied considerably depending upon the range of available bacterial concentrations used to estimate them; high correlation coefficients were obtained in all cases. The use of low bacterial cell concentrations yielded lower values for the number of sites and much higher values for the affinity constant than did the use of high bacterial cell concentrations. When data covering the entire range of bacterial concentrations were employed, values for the number of sites and the affinity were similar to those obtained by using only high bacterial cell concentrations. The simplest explanation for these results is that there are multiple binding sites for S. sanguis on saliva-treated hydroxyapatite surfaces. When present in low concentration, the streptococci evidently attach to more specific high-affinity sites which become saturated when higher bacterial concentrations are employed. The possibility of multiple binding sites was substantiated by comparing estimates of the adsorption parameters from a computer-simulated isotherm with those derived from the experimentally generated isotherm. A mathematical model describing bacterial adsorption to binary binding sites was further evidence for the existence of at least two classes of binding sites for S. sanguis. Far fewer streptococci adsorbed to experimental pellicles prepared from saliva depleted of bacterial aggregating activity when low numbers of streptococci were used, but the magnitude of this difference was considerably less when high streptococcal concentrations were employed. This suggests an association between salivary components which possess bacterial-aggregating activity and bacterial adsorption to high-affinity specific binding sites on saliva-treated hydroxyapatite surfaces.

Adsorption↗
PubMed1983

Association of neuraminidase-sensitive receptors and putative hydrophobic interactions with high-affinity binding sites for Streptococcus sanguis C5 in salivary pellicles.

The relationship of neuraminidase-sensitive receptors and putative hydrophobic interactions to high- and low-affinity binding sites in experimental salivary pellicles for Streptococcus sanguis C5 was investigated. NaSCN, an inhibitor of hydrophobic interactions, reduced the number of cells which adsorbed to pellicles to a greater extent than NaCl or KCl when both low and high streptococcal concentrations were used in assays. However, NaSCN was not more effective than NaCl or KCl in desorbing 3H-labeled salivary pellicle components from hydroxyapatite, and NaSCN pretreatment of either strain C5 cells or the salivary pellicles did not destroy or remove either the streptococcal adhesions or the pellicle receptors. Neuraminidase treatment of pellicles or the presence of sialic acid-containing gangliosides only inhibited S. sanguis adsorption when low streptococcal concentrations were used. At these concentrations, S. sanguis adsorbs primarily to high-affinity pellicle binding sites. Adsorption isotherms indicated that neuraminidase-sensitive interactions were mainly responsible for the high affinity of these binding sites, whereas putative hydrophobic interactions inhibitable by NaSCN were mainly associated with the numbers of binding sites available. Sugar inhibition studies suggested that the two classes of binding sites previously demonstrated in untreated salivary pellicles for S. sanguis C5 are not the result of a partial conversion of high-affinity sites to low-affinity sites due to removal of sialic acid residues.

Adsorption↗
PubMed1982

Adsorption thermodynamics of acidic proline-rich human salivary proteins onto calcium apatites.

The thermodynamics of adsorption of four acidic proline-rich salivary proteins from their aqueous solutions onto hydroxyapatite (HA) and fluorapatite (FA) have been analyzed. Enthalpies and entropies of adsorption were derived from isotherms at 37 degrees C and 4 degrees C and led to the unexpected conclusion that adsorption of the macromolecules studied is an endothermic process. Consequently, adsorption is driven by an increase in entropy. Most of this increase originates in the adsorbate molecules, probably through disruption of internal ion pairs, hydrogen bonds, and displacement of water molecules. Integral free energies of adsorption (delta G) and the partial contributions of adsorbent and adsorbate were both calculated as a function of the adsorption coverages. For equal coverages (of each adsorbate), delta G is lower with FA than with HA. Most of the contribution to delta G originates from the adsorbate, although the adsorbent contribution becomes significant as adsorption saturation is approached. The differences in the various thermodynamic quantities are qualitatively related to the known structural features of the four proteins. The results are important in understanding the role played by the proline-rich proteins in the oral environment.

Adsorption↗
PubMed1982

Equilibrium dialysis and ultrafiltration studies of calcium and phosphate binding by human salivary proteins. Implications for salivary supersaturation with respect to calcium phosphate salts.

Previous ultrafiltration studies indicated that up to one-half of the calcium and two-thirds of the phosphate in human salivary secretions may be bound by salivary proteins. Since this binding is an important variable in determining the extent of salivary supersaturation with respect to calcium phosphate salts, and since the amount of binding reported is surprisingly large, calcium and phosphate ion-binding by salivary macromolecules has been reexamined. From experiments using equilibrium dialysis, it was found that (1) the fraction of salivary calcium involved in macromolecular complexes ranges from a few percent for unstimulated secretions, to no more than about 10% for stimulated glandular salivas, and (2) salivary proteins do not bind phosphate ions to any significant extent. These findings, and experiments using an improved ultrafiltration membrane, indicate that the earlier results were artifacts of the ultrafiltration technique. Fractionation of salivary proteins, followed by equilibrium dialysis measurements, showed that the anionic proline-rich proteins and a basic proline-rich glycoprotein are responsible for most of the calcium binding now observed. The finding that macromolecular complexes of salivary calcium and phosphate have been overestimated in the past, leads to the conclusion that salivary calcium and phosphate ion activities in stimulated salivary secretions may be up to 50 to 100% higher than previously thought. Revised values were therefore used to recalculate the degree of salivary supersaturation with respect to calcium phosphate salts. The results indicate that stimulated salivary secretions are supersaturated with respect to dicalcium phosphate dihydrate; this is a substantially greater degree of supersaturation than previously reported.

Calcium Phosphates↗
PubMed1982

Effect of fluoride on crystal growth of calcium apatites in the presence of a salivary inhibitor.

The effect of fluoride on the kinetics of crystal growth of calcium apatites was studied using seed crystals of hydroxyapatite coated with PRP-3, a proline-rich phosphoprotein salivary inhibitor of crystal growth. Initial precipitation rates in the presence of PRP-3, under conditions of partial inhibition, were enhanced by fluoride, effectively counteracting the inhibitory activity of the macromolecule. This rate enhancement is related to an increase in the precipitation driving force, i.e., the degree of supersaturation with respect to the precipitating phase; in this case a fluoridated hydroxyapatite. The growth of this phase takes place at the uncovered crystal growth sites which have been previously shown to be the same sites as the adsorption sites for the protein inhibitors. Explanations based on fluoride activation of secondary crystal growth sites and on the displacement of adsorbed inhibitor by fluoride are not substantiated by the present results. It has been demonstrated that under conditions of maximum coverage of available crystal growth sites by PRP-3, resulting in no apparent crystal growth, measurable crystal growth is observed upon the addition of fluoride (1 ppm). This phenomenon is best explained by the fact that at maximum PRP-3 coverage, a small number (16%) of crystal growth sites remain uncovered, which support an unmeasurable rate of crystal growth. Upon the addition of fluoride, this rate is significantly enhanced. It is suggested that the fraction of uncovered growth sites is related to steric interactions of the PRP-3 molecule in the adsorbed state. Overall, the results presented suggest that fluoride can accelerate crystal growth in an environment such as the enamel surface where the acquired pellicle is formed.

Crystallization↗
PubMed1981

Crystal growth of calcium apatites in dilute solutions containing fluoride.

The kinetics of seeded crystal growth of calcium apatites were studied in dilute supersaturated solutions at various levels of fluoride concentrations. Initial precipitation rates were enhanced by fluoride concentrations higher than 0.05 ppm. The analytical results are consistent with the precipitation of fluoridated hydroxyapatites, Ca5Fx-(OH)1-x(PO4)3, FHA. The degree of fluoridation, X, appears to be determined by the activity of HF in solution, which varies for the various initial fluoride levels but remains fairly constant during precipitation. Thus the composition of the precipitating phase was the same for a given solution whether 25 or 10 mg of hydroxyapatite was added as seeds. All the experimental results are consistent with the BCF theory, which relates the mean linear rate of growth, RL, to the supersaturation, DS, by the expression RL = C1T(DS-1)1n(DS)tanh(C2/T 1n DS), in which DS is the supersaturation defined by mean molar activities with respect to the precipitating FHA, T the absolute temperature, and C1 and C2 are constants calculated from the experimental results. Consequently, the crystal growth appears to take place in surface kinks and to be controlled by surface diffusion. Since crystal growth in most biological systems takes place at fluoride concentrations within the experimental range used, it seems probable that it occurs along the model advanced in the present investigation.

Apatites↗
PubMed1979

Effect of human salivary proteins on the precipitation kinetics of calcium phosphate.

Inhibition of calcium phosphate precipitation in saliva, and prevention of the formation of mineral accretions on tooth surfaces, has been ascribed to the existence of inhibiting salivary macromolecules. Marked reductions in the crystal growth rate of hydroxyapatite (HA) seeds were measured in supersaturated solutions containing either of two proline-rich proteins, PRP1 or PRP3, or statherin; the three macromolecules were isolated from human parotid saliva. The reductions were also observed when the HA seeds were pretreated with solutions of the macromolecules before adding them to the supersaturated calcium phosphate solution. This effect was very similar in the case of the two PRPs and it was directly related to the extent of adsorption site coverage of these proteins on the HA seeds. The effect of statherin was larger than anticipated from its adsorption behavior. However, comparison on the basis of number of moles adsorbed per unit area of HA shows that the PRP are more effective inhibitors than statherin. The macromolecule concentrations used were considerably lower than those in the salivary secretions, therefore these macromolecules could readily prevent mineral accretion on tooth surfaces through their adsorption onto the enamel surface.

Adsorption↗
PubMed1979

Demineralization and remineralization of dental enamel.

Experimentation in vitro using organic acid buffers as demineralizing media shows that caries-like lesions can be obtained which are very similar in morphology and developmental stages to early lesions formed naturally under oral conditions. The use of these chemical systems and of mechanistic models advanced to explain the unique histological features of incipient caries have yielded a good understanding of the processes involved in caries formation. The study of natural and induced factors influencing the demineralization process has been greatly facilitated by the use of bacteriological systems in which demineralization is produced by direct colonization of cariogenic microorganisms on the surfaces of extracted teeth. Comparison of results obtained with these latter systems and with chemical systems has allowed us, for example, to elucidate the mechanism by which acquired salivary pellicles and fluoride topical solutions decrease the rate of enamel demineralization. The pellicle retards transport of matter across the enamel surface, whereas the fluoride topical solutions decrease the cariogenicity of the colonizing bacteria.

Acids↗
PubMed1979

Differential adsorption and chemical affinities of proteins for apatitic surfaces.

Studies are reviewed which identify the interacting groups involved in protein adsorption onto hydroxyapatite. Thus, carboxyl and phosphoester groups bind to calcium sites in the adsorbent, and basic groups bind to phosphate sites. Detailed adsorption studies have been performed to quantitate some of these interactions. An adsorption model, based on the Langmuir adsorption isotherm, adequately fitted the data from experiments using selected amino acids, bovine albumin and two human salivary proteins. Adsorption parameters (affinities and maximum number of sites) were obtained for several apatitic adsorbents, with affinities increasing considerably in the series hydroxy- (HA), fluorhydroxy- (FHA) and fluorapatite (FA). A modest increase in the number of sites was also noted. The change in adsorption behavior, with increasing fluoride content, was attributed to a reduction in the surface free energy of the adsorbent, with a concomitant decrease in the interaction of the adsorbent with water, and a consequent enhancement of the adsorption bond. It is suggested that this effect may play a role in the cariostatic effect of fluoride. Unusual structural aspects of the salivary proteins are discussed in relation to their adsorption behavior, and the molecular segments responsible for binding to the adsorbent tentatively identified.

Adsorption↗