2.7.8.8 cardiolipin activates. The enzyme is completely desensitized by treatment for 5 min at 40°C against the effect of cadiolipin without loss of activity 643784 2.7.8.8 diphosphatidylglycerol membrane association and activity of PtdSer synthase is increased, studied with mixed micelles containing phosphatidylglycerol (one charge) or diphosphatidylglycerol (two charges), the two main anionic membrane lipids in Escherichia coli 661745 2.7.8.8 additional information activity of phosphatidylserine synthase depends significantly on the nature and level of the lipids in the matrix, at which the enzyme is operating 661745 2.7.8.8 additional information optimal activity is dependent on ionic strength, 0.3 or higher 643778 2.7.8.8 additional information the enzyme reconstituted with lipid vesicles of various compositions exhibits practically no activity in the absence of a detergent and with the substrate CDP-diacylglycerol present only in the lipid vesicles. Inclusion of octylglucoside in the assay mixture increases the activity 20- to 1000fold, the degree of activation depends on the lipid composition of the vesicles. Inclusion of additional CDP-diacylglycerol in the assay mixture increases the activity 5- to 25-fold. When the fraction of phosphatidylglycerol is increased from 15 to 100 mol% in the vesicles the activity increases 10fold using the assay mixture containing octylglucoside. The highest activities are exhibited with the anionic lipids diphosphatidylglycerol and phosphatidic acid while phosphatidylinositol gives lower activity 643796 2.7.8.8 phosphatidylethanolamine slightly activates. The enzyme is completely desensitized by treatment for 5 min at 40°C against the effect of phosphatidylethanolamine without loss of activity 643784 2.7.8.8 phosphatidylglycerol membrane association and activity of PtdSer synthase is increased, studied with mixed micelles containing phosphatidylglycerol (one charge) or diphosphatidylglycerol (two charges), the two main anionic membrane lipids in Escherichia coli 661745 2.7.8.8 Triton X-100 dependent on nonionic detergent, at 0.1 mM CDP-diacylglycerol optimal activity occurs at a Triton to substrate molar ratio of 8:1 643779 2.7.8.8 Triton X-100 enzyme is dependent on a nonionic detergent such as Triton X-100 643778 2.7.8.8 Triton X-100 increasing levels of Triton X-100 at low molecular ratios of Triton X-100 to CDP-diacylglycerol stimulate 643782