- The properties of phosphatidyl-L-serine (L-PS) and phosphatidyl-D-serine (D-PS) were compared. The two forms of PS have similar but nonidentical L to L phase transition temperatures. Mixtures of phosphatidylserine with phosphatidylethanolamine and cholesterol (molar ratio 1:1:2) show polymorphic behavior at higher temperatures and in the presence of Ca2+. Mixtures with L-PS undergo conversion to nonlamellar phases at lower temperatures than do similar mixtures with D-PS. The aggregation of vesicles upon addition of histones is greater for L-PS than for D-PS. With fluorescence digital imaging microscopy we could show differences in the extent of formation of histone-induced domains enriched in PS or in diacylglycerol. The most enriched domains were induced with histone in membranes containing L-PS. The MARCKS peptide showed no differences in domain formation between L-PS and D-PS. The maximal activity of protein kinase C was greater in the presence of L-PS when histone, which could form more enriched domains, was the substrate. However, with a MARCKS peptide substrate, which formed domains of equal enrichment with L-PS and D-PS, the maximal activity of protein kinase C was the same with D-PS and with L-PS. These observations demonstrate that L-PS and D-PS have different physical properties. These differences likely contribute to the greater ability of L-PS to activate protein kinase C.