Decarboxylation of phosphatidylserine by rat liver mitochondria

1. The decarboxylation of phosphatidylserine was studied using particles obtained by sonication of rat liver mitochondria as the source of the enzyme, and liposomes prepared from total microsomal phospholipids labelled in phosphatidylserine. The reaction was followed by measuring formation of either CO2 or phosphatidylethanolamine. 2. The reaction was inhibited when isotonic sucrose was substituted by equiosmotic solutions of electrolytes (acetate or phosphate). 3. Optimum pH for the reaction was 5.0 - 5.2. 4. At pH 7.4 the reaction was stimulated by the cytoplasmic fraction from rat liver, most likely due to the action of phospholipid transfer protein(s). 5. The reaction was stimulated by Mg2+ and Mn2+. Maximum stimulation occurred at 2 - 3 mM-concentration of the divalent cation.