PubMed · 8417769
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T H Smith. 1993-01-09. Hidden sugars.. https://doi.org/10.1038/sj.bdj.4808059
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During apoptosis, DNA fragmentation and intracellular acidification occur concurrently. Previous results have shown that intracellular acidification is not required for DNA fragmentation, while the alternative, that acidification is a consequence of DNA fragmentation was analyzed here. To obviate the requirement of any nuclear function in acidification, apoptosis was induced by staurosporine in cytoplasts made from the breast tumor cell line MDA-MB-468. Both cells and cytoplasts demonstrated externalization of phosphatidylserine that was prevented by the pan-caspase inhibitor zVAD-fluoromethylketone or by expression of Bcl-2. Intracellular acidification was observed in both cells and cytoplasts and this was also inhibited by both zVAD-fluoromethylketone and Bcl-2. These results show that intracellular acidification and DNA fragmentation are independent consequences of caspase action during apoptosis.
Jovin and co-workers have demonstrated that DNA strands containing guanine-adenine repeats generate a parallel-stranded homoduplex. Here we propose that the homoduplex is a dimer of the ordered single strand discovered by Fresco and co-workers at acid pH. The Fresco single strand is shown here to be stabilized in aqueous ethanol where adenine is not protonated. Furthermore, we demonstrate that the strands dimerize at higher salt concentrations without significantly changing their conformation, so that the dimerization is non-cooperative. Hence, the Jovin homoduplex can form through a non-cooperative dimerization of two cooperatively melting single strands. The available data indicate that the guanines stabilize the Fresco single strand whereas the adenines cause dimerization owing to their known intercalation or clustering tendency. The guanine-adenine repeat dimer seems to be a DNA analog of the leucine zipper causing dimerization of proteins.
The aim of this study was to test the hypothesis that xylitol, alone and in combination with fluoride, affects the salivary flow rate and micro-biota, dental plaque accumulation, gingivitis development, and the acidogenic potential of plaque. Three groups, each of 10 subjects, rinsed for 1 min 3 times daily over two 4-week periods, first with 10 ml water (control), and thereafter with either 0.05% NaF, 40% xylitol, or with 0.025% NaF plus 20% xylitol according to a double-blind controlled design. They performed habitual mechanical tooth cleaning during the first 2 weeks of each period but abstained from interdental cleaning during the final 2 weeks. While mouth rinsing was continued, all mechanical oral hygiene was discontinued the last 2 days of each period to permit plaque accumulation. The last mouth rinse was administered in the clinic before the final examination. The following parameters were assessed: (1) unstimulated and paraffin-stimulated salivary secretion rates; (2) salivary micro-biota; (3) plaque index; (4) papillar bleeding; (5) plaque pH response to sucrose, and (6) lactate formation by dental plaque. No statistically significant differences in any of the parameters were found. In conclusion, three daily mouth rinses with fluoride and xylitol, separately or in combination, did not affect the salivary flow rate or micro-biota, dental plaque accumulation, gingivitis development, or the acidogenic potential of plaque.