Modification of membrane lipids. Phenethyl alcohol-induced alteration of lipid composition in Tetrahymena membranes.

Tetrahymena pyriformis NT-I cells in the early-logarithmic phase were incubated with phenethyl alcohol (2-phenylethanol) and effects on the lipid composition were examined in various membranes. 1. There was a marked modification in phospholipid head, as well as fatty acyl group composition in pellicles, mitochondria and microsomes of the phenethyl alcohol-treated cells. Compared with membranes of the control cells, the membranes from phenethyl alcohol-treated cells were found to contain a higher level of phosphatidylcholine content with the compensating decrease in phosphatidylethanolamine, while 2-aminoethylphosphonolipid showed only a slight decrease in these membranes. The acyl group profile of membrane phospholipids in the presence of phenethyl alcohol was also modified so that a profound elevation of the content of polyunsaturated fatty acids, linoleic and gamma-linolenic acids. The major monounsaturate, palmitoleate decreased. Such lipid alteration is a reversible process, and therefore upon removal of phenethyl alcohol the modified lipid composition returned to normal. 2. By freeze-fracture electron microscopy in combination with temperature quenching, the outer alveolar membrane of the phenethyl alcohol-treated cell was observed to reveal less aggregation of intercalated-membrane particles, as compared with the control membrane. The quantitative analysis of the thermotropic lateral movement of membrane particles provided evidence that the membrane in the phenethyl alcohol-treated cell became more fluid. Such fluidizing effects may result from an increase in the acyl group unsaturation and also in the phosphatidylcholine content. 3. With regard to the mechanism responsible for the marked decrease in palmitoleate in membrane phospholipids, there was found a depressed conversion of the palmitate to palmitoleate in the phenethyl alcohol-treated cells. It was further suggested that the drug may have an inhibitory effect on the synthesis of palmitoyl-CoA desaturase involving the (16 : 0 leads to 16 : 1) conversion. Also, it was demonstrated that the increase in a precursor-product fashion of phosphatidylcholine with the corresponding decrease in phosphatidylethanolamine was not due to transformation of phosphatidylethanolamine to phosphatidylcholine through stepwise methylation.