MODULATION OF PHOSPHOLIPID BASE EXCHANGE ENZYMES IN ACANTHAMOEBA PALESTINENSIS

Abstract

Quantitative changes in amounts of the enzymes governing exchange between free- and phospholipid alcoholic amines in membranes of the soil amoeba Acantharnoeba palestinensis have been produced by manipulation of intracellular pool levels of soluble alcoholic amines. Following growth of cells in media containing 10mM choline, 10mM ethanolamine or 20mM L-serine for 24hr, intracellular pools of these bases were elevated 8-fold, 20-fold and 13-fold greater than normal, respectively. Total cell particulate activities and specific activities of all three exchange enzymes were greatly increased in the presence of elevated choline and greatly decreased in the presence of elevated serine. High ethanolamine pool levels led to increased choline and ethanolamine exchange enzyme amounts with no significant changes detectable in the amount of the serine exchange enzyme. No significant change in total cell lipid phosphorus was observed, indicating a lack of increased phospholipid synthesis. Upon analysis of the rough endoplasmic reticulum, which is one site known to contain the exchange enzymes, a somewhat different pattern than that observed in the total cell particulates emerged. This might have indicated that different changes in the exchange enzymes occurred in yet other cellular membranes where they were localized. In the rough endoplasmic reticulum the specific activities of all three exchange enzymes were greatly enhanced following choline and ethanolamine pool elevations and slightly enhanced following serine pool elevation. In addition, the lipid phosphorus to protein ratio was elevated to varying degrees in the endoplasmic reticulum isolated from the treated cells. The increases in specific activities of the exchange enzymes were positively correlated with the changes in total phospholipid content of the rough endoplasmic reticulum. In choline treated cells, but not the cells with elevated ethanolamine or serine levels, the phosphatidyl choline content was increased about 9% above control levels with corresponding decreases in phosphatidyl ethanolamine and phosphatidyl serine content The data indicate a regulatory interrelationship between soluble intracellular alcoholic amines, exchange enzymes and membrane phospholipids.