Short- and long-range Ca2+-induced lateral phase separations in ternary mixtures of phosphatidic acid, phosphatidylcholine and phosphatidylethanolamine
✍ Scribed by Kazuo Ohki; Kiyoko Takahashi; Satoru Kato; Akikazu Maesono
- Publisher
- Elsevier Science
- Year
- 1989
- Tongue
- English
- Weight
- 691 KB
- Volume
- 50
- Category
- Article
- ISSN
- 0009-3084
No coin nor oath required. For personal study only.
✦ Synopsis
Ca2*-induced lateral phase separation in an equimolar ternary mixture of dipalmitoylphosphatidic acid (DPPA), dipalmitoylphosphatidylcholine (DPPC) and dimyristoylphosphatidylethanolamine (DMPE) was investigated by high-sensitivity differential scanning calorimetry. The thermogram showed a merged phase transition of these components in the absence of calcium ions, and the addition of calcium ions induced a change in the thermogram of the ternary mixture in a biphasic fashion. Different features were observed below and above a Ca2÷/DPPA molar ratio of 1. When the ratio was below 1, the transition peak shifted to a higher temperature. Within a range above 1, a major transition peak appeared at a temperature similar to the transition temperature of a binary mixture of DPPC and DMPE. The same tendency was observed in the ternary mixture in which DMPE was replaced with dilauroylphosphatidylethanolamine (DLPE) or dipalmitoylphosphatidylethanolamine (DPPE). The features of these thermograms below and above a Ca2÷/DPPA ratio of 1 could be attributed to Ca2÷-induced lateral phase separations of DPPA molecules in short-range and long-range phase separations, respectively. In order to confirm the shortrange phase separation, the Ca ~' effect on an equlmolar ternary mixture of DPPA, DPPC and DMPE was examined using a spin-spin exchange interaction of stearate methyl ester spin probes. The results indicate that the long-range phase separation of phosphatidic acid induced by calcium ions is suppressed in ternary mixtures at low concentrations of Ca 2÷.