The Primary Structure of the Phosphatidylcholine‐Exchange Protein from Bovine Liver

The phosphatidylcholine exchange protein from bovine liver consists of a single polypeptide chain and has a blocked N terminus. The protein contains an estimated 244 amino acid residues in accordance with a determined molecular weight of 28000. The protease from mouse submaxillaris gland cleaved the citraconylated and S-carboxymethylated derivative of the exchange protein at one specific site (Arg14-Glu15) close to the N terminus. Analysis of the two resulting peptides showed that N-acetyl-methionine was the N-terminal residue and gave the sequence of the first 41 residues. The modified protein was also fragmented with the protease from Staphylococcus aureus. The peptides isolated represented 88% of the protein; their sequences were determined by manual and automated Edman degradation. Alignment of a number of these peptides gave the complex sequence of the N-terminal half up to position 122.