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Biomedical subjects

M Kresak

Publications and source records attributed to M Kresak.

7 recordsLinked to original sources
PubMed1989

Possible roles of partial sequences at N- and C-termini of amelogenin in protein-enamel mineral interaction.

The purpose of this study was to assess the functional significance of homologous sequences of mammalian amelogenins at their N- and C-termini. A porcine 5-kDa fragment corresponding to the N-terminal 45 residues of amelogenins was purified from the secretory enamel. The decapeptide TDKTKREEVD corresponding to the C-terminal 10 residues of amelogenins was synthesized according to conventional solid-phase procedures. The inhibitory activity of both moieties on apatite crystal growth was determined in a supersaturated solution having an ionic composition similar to that of the fluid phase separated from porcine secretory enamel. The 5-kDa amelogenin fragment was sparingly soluble in neutral solutions and (in condensed forms because of aggregation) showed no significant inhibition of crystal growth, whereas the fragment molecules pre-adsorbed onto the seed crystals yielded modest inhibition of hydroxyapatite precipitation. However, their inhibitory activity was significantly lower than that of parent porcine amelogenin (25-kDa molecular mass). The high solubility of synthesized decapeptide allowed us to determine the adsorption isotherm onto hydroxyapatite at 37 degrees C, at an ionic strength similar to that of the enamel fluid. The obtained adsorption isotherm was described by a Langmuir model; the adsorption affinity and the maximum adsorption sites were 6.2 mL/mumol and 0.53 mumol/m2, respectively. As expected from the low adsorption affinity, the peptide showed a much weaker inhibition of apatite crystal growth than the parent amelogenin.(ABSTRACT TRUNCATED AT 250 WORDS)

Adsorption↗
PubMed1984

Adsorption of molecules of biological interest onto hydroxyapatite.

Equilibrium and kinetic experiments were conducted to investigate the factors determining the adsorption of salivary macromolecules onto hydroxyapatite. Using amino acids and other small adsorbates, it was determined that the carboxyl attached to the alpha carbon does not appear to adsorb onto HA and the affinities of side-chain carboxyls are much smaller than that of the phosphate group (phosphoserine). Hydroxyl (serine) displays an extremely high affinity, but its adsorption site on HA is different and the number of such sites is much smaller than found for the rest of the functional groups investigated. It is shown that the information obtained from small molecules cannot be readily applied to prediction of the adsorption behavior of salivary macromolecules and polypeptides. The kinetics of adsorption of the salivary phosphopeptide statherin, a polyaspartate, and the salivary prolinerich phosphoprotein PRP3 are consistent with the reversibility of the adsorption process; no conclusion was possible in the case of the protein PRP1. Apparent irreversibility cannot be explained on the basis of multipoint binding or the properties of the carboxyl versus phosphate group; it appears that secondary structure determines to a significant extent the adsorption properties of the macromolecules. Calculation of the thermodynamic molar quantities of adsorption of PRP1, PRP3, and L-ASP onto HA showed that the process is entropically driven. The functional relationship between partial molar entropy and adsorption coverage is similar for the two proteins, but quite different from that for aspartate. Explanations for these results are advanced on the bases of changes in structure configurations and displacement of water from the adsorbate and the adsorbent surface, the second factor being the dominant one in the adsorption of a small molecule such as L-ASP.

Absorption↗
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

In vitro evaluation of editempa on hydroxyapatite formation and its effects on dental enamel.

N,N,N',N' ethylene diamine tetra (methylene phosphonic acid)-Editempa inhibited the formation of hydroxyapatite (HA) in vitro at 4 ppm. In the seeded crystal growth of HA at 37 degrees C, it completely inhibited the crystal growth at 0.5 ppm. C14-Editempa adsorbed to HA crystal at 37 degrees C. The maximum adsorption was 1.29 mumol/m2 of HA and the adsorption was monolayer. Compared to the natural inhibitors of HA in saliva (Statherin and Proline-rich proteins), Editempa was more effective in vitro on weight basis. At 0.3 ppm, it inhibited growth rate of the crystals by 80% while 4 to 5 ppm of the natural inhibitors were needed to get the same effect. The inhibition of rates with Editempa was not directly proportional to the area covered by it on the HA seeds (occupied less than 10% of the surface). The natural inhibitors, on the other hand, seemed to cover all the available surface. These data indicate that the inhibition with Editempa was due to binding to specific sites on the surface of the seeds. The solutions up to 5% of Editempa did not damage or etch the surface of human dental enamel in vitro at pHs 5.0 and 7.5, as evaluated by scanning electron microscopy and calcium released in the exposed solutions.

Adsorption↗