Studies on thermal adaptation in Tetrahymena membrane lipids. Modification of positional distribution of phospholipid acyl chains in plasma membranes, mitochondria and microsomes.

The positional distribution of fatty acyl chains in major glycerophospholipids (phosphatidylethanolamine, phosphatidylcholine and 2-aminoethylphosphonolipid) of three membrane fractions (plasma membranes, mitochondria and microsomes) of the thermotolerant Tetrahymena pyriformis NT-1 cells was analyzed at various time intervals within 10 h after a temperature shift from 39 to 15 degrees C. During this period of acclimation there were no changes in both the total phospholipid content and its proportional composition. At the 1-position, the content of palmitate in phosphatidylethanolamine (present solely in diacyl type), diacylphosphatidylcholine, and diacyl-(2-aminoethyl)phosphonolipid was decreased progressively after temperature-shift, while gamma-linolenate increased in a complementary fashion, in mitochondria and microsomes. The increase in the percentage of linoleate was compensated by the decrease in oleate at the 2-position of two 1,2-diacylphospholipids. On the other hand, as for 1-alkyl-2-acyl-phospholipids, a marked increment in gamma-linolenate occurred, with a decline of oleate and linoleate at the 2-position of 1-alkyl-2-acyl-phosphatidylcholine, but no significant alterations were seen at the 2-position of 1-alkyl-2-acyl-(2-aminoethyl)phosphonolipid. The results suggest that the newly modified phospholipid molecular species such as 1-gamma-linolenoyl-2-linoleoyl-phosphatidylethanolamine and 1-hexadecyl-2-gamma-linolenoyl-phosphatidylcholine disseminate rapidly to other cell compartments and that they would play a pivotal role in the adaptive amelioration of altered membrane physical states during the cold acclimation.