The properties of an enzyme system degrading endogenous phospholipids of Tetrahymena pyriformis

Triacylglycerol turnover in Tetrahymena pyriformis. Relation to phospholipid synthesis

The metabolic function of triaclyglycerol in Tetrahymena pyriformis was investigated by prelabeling endogenous lipid with a 14C-labeled short chain fatty acid, and then following the disappearance of radioactivity from triacylglycerol and its appearance in other products. In 90 min, up to 85% of the label in triacylglycerol turns over, and although some radioactivity appears in CO2 and glycogen, most of the label appears in phospholipid. Starvation of the cells, as well as resuspension in enriched medium or provision of acetate all block triacylglycerol breakdown, while supplementation of the medium with pyruvate does not. Prelabeling lipid with [3H] glycerol shows that some of the transfer of material from triacylglycerol to phospholipid involves transfer of the glycerol backbone, although transfer of triacylglycerol fatty acids directly to phospholipid probably also occurs. In addition, the catabolism of triacylglycerol occurs by a "last-in-first-out" mechanism, indicating some form of compartmentation of triacylglycerol in this cell. The results demonstrate an important metabolic interrelationship between triacylglycerol catabolism and phospholipid synthesis and raise the question, in this cell at least, of the validity of considering triacylglycerol only as a fuel storage form.

Studies of membrane formation in Tetrahymena pyriformis. II. Isolation and lipid analysis of cell fractions

A method has been devised to fractionate cells of Tetrahymena pyriformis, yielding pure or highly enriched preparations of cilia, cilia-associated soluble material, pellicles, mitochondria, microsomes, and postmicrosomal supernatant. The method prevents the destructive action of lipolytic enzymes commonly associated with this organism. Analysis of the membrane lipids of these fractions reveals significant differences in lipid composition. Most noteworthy are the high concentrations of phosphonolipid and tetrahymanol in the surface membranes.