Identification of the phospholipid bound to EPCR. (A) Lane 1 indicates that a mixture of PE and PCh was loaded as standard; lane 2, lipid fraction extracted from yeast-produced sEPCR; lane 3, lipid fraction extracted from yeast-produced murine sEPCR; and lane 4, lipid fraction from sEPCR produced in a mammalian expression system. (B) MS/MS fragmentation analysis of the lipid fraction from yeast-produced sEPCR. The peak at m/z 786 matches up with commercial PCh. The spectrum generated by fragmentation of the molecule at m/z 786 fits properly with commercial PCh. The different PCh polar group fragmentation products and their respective m/z are started.