ROLE OF PHOSPHOLIPIDS CONTAINING DOCOSAHEXAENOYL CHAINS IN MODULATINGTHE ACTIVITY OF PROTEIN-KINASE-C

It is known that the phospholipids of the brain cells of fish are alte red during cold adaptation, In particular, the l-monounsaturated 2-pol yunsaturated phosphatidylethanolamines (PEs) increase 2- to 3-fold upo n 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 th at it was more effective in lowering this transition temperature than were other, less unsaturated, PE species, In addition, it was not simp ly 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 e ffect on this transition temperature. Zwitterionic substances that lo, ver 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, PE s, 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 consequen ce of this lipid's increasing the partitioning of PKC to the membrane.