PubMed · 6951636
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S Mante, W W Yotis. 1982. Fluoride accumulation by Streptococcus mutans from a low ionic medium.. https://doi.org/10.1159/000260590
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The ability of gellan to form gels in the presence of calcium ions enabled us to prepare capsules by gelation of this polysaccharide around a core containing starch, calcium chloride and a model drug. Release from the dried capsules was studied in vitro by means of the rotating basket technique (USP) in different environmental conditions (distilled water, pH = 2.0, pH = 6.8) and the effects of the presence of increasing amounts of drug in the formulation were also investigated. The behaviour of the gellan capsules was compared with that of beads prepared with the same polysaccharide but containing different additives. Results obtained indicate that gellan is suitable for the formulation of sustained release capsules and that solvent uptake by the dried capsules is most likely the main factor capable of affecting the rate of delivery from the tested preparations.
PURPOSE: To study the thermal stability of recombinant human deoxyribonuclease I (rhDNase) in aqueous solutions. METHODS: Differential scanning calorimetry (DSC) was used to measure the denaturation or melting temperature (T(m)) and enthalpy (H(m)) of rhDNase. The effects of denaturants (guanidine HCl and urea) and additives (mainly divalent cations and disaccharides) were investigated at pH 6-7. RESULTS: The T(m) and H(m) of rhDNase in pure water were measured as 67.4 degrees C and 18.0 J/g respectively, values typical of globular proteins. The melting peak disappeared on re-running the sample after cooling to room temperature, indicating that the thermal denaturation was irreversible. The latter was due to the occurrence of aggregation accompanying the unfolding process of rhDNase. Size exclusion chromatography indicated that during heat denaturation, rhDNase formed soluble high molecular weight aggregates with a molecular size >300kD estimated by the void volume. Of particular interest are the divalent cations: Ca(2+) stabilizes rhDNase against thermal denaturation and elevates T(m) and H(m) while Mg(2+), Mn(2+) and Zn(2+) destabilize it. Sugars also stabilize rhDNase. As expected, denaturants destabilize the protein and lower the T(m) and H(m). All destabilization of rhDNase can be prevented by adding Ca(2+) to the solutions. CONCLUSIONS: CaCl(2) and sugars were found to stabilize rhDNase against thermal denaturation while divalent cations, urea and guanidine HCl destabilize the protein. The effects could be explained by a mixture of mechanisms. For Ca(2+) the protective effect is believed to be due to an ordering of the rhDNase structure in its native state, and by prevention of breaking of a disulfide bridge, thus making it less susceptible to unfold under thermal stress.
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