Role of phospholipids containing docosahexaenoyl chains in modulating the activity of protein kinase C.
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It is known that the phospholipids of the brain cells of fish are altered during cold adaptation. In particular, the 1-monounsaturated 2-polyunsaturated phosphatidylethanolamines (PEs) increase 2- to 3-fold upon adaptation to cold. One of the most striking changes is in the 18:1/22:6 species of PE. We determined how this lipid affected the bilayer-to-hexagonal-phase transition temperature of 16:1/16:1 PE. We found that it was more effective in lowering this transition temperature than were other, less unsaturated, PE species. In addition, it was not simply the presence of the 18:1/22:6 acyl chains which caused this effect, since the 18:1/22:6 species of phosphatidylcholine had the opposite effect on this transition temperature. Zwitterionic substances that lower the bilayer-to-hexagonal-phase transition temperature often cause an increase in the activity of protein kinase C (PKC). Indeed, the 18:1/22:6 PE caused an increase in the rate of histone phosphorylation by PKC which was greater than that caused by other, less unsaturated, PEs. The 18:1/22:6 phosphatidylcholine had no effect on this enzyme. The stimulation of the activity of PKC by the 18:1/22:6 PE is a consequence of this lipid's increasing the partitioning of PKC to the membrane.
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