Abstract
Changes in phospholipid composition and phospholipase D activity were observed during a differentiation from haploid myxoamoebae to diploid plasmodia of a true slime mold, Physarum polycephalum. In the amoeboid stage, the main components of phospholipid fraction were phosphatidylethanolamine (PE, 43.3%), phosphatidylcholine (PC, 28.8%) and phosphatidylinositol (PI, 8.0%), but in the plasmodial stage, PC was dominant (40.7%) and other main components were PE (31.5%) and phosphatidic acid (PA, 11.0%). The specific activity of phospholipase D in the plasmodia was 5.7-times higher than that in the myxoamoebae when measured in the presence of Ca 2+ at the alkaline pH. In the amoeboid stage, phospholipase A activity (A 1 or A 2) was detected at the alkaline pH with Ca 2+. Phospholipase D activity in the plasmodia was characterized: pH optimum was 6.0; Ca 2+ was required for the reaction and Ba 2+ could substitute partly for Ca 2+; PE was the best substrate for the hydrolytic activity and PC and PI were not appreciably hydrolyzed; and all detergents tested inhibited the enzyme activity.
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