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Pulmonary surfactant is a lipid-protein complex synthesized and secreted by the alveolar epithelium of lungs,including lipids(90%)and proteins(10%).More specificially contains mainly phospholipids,neutral lipids and surfactant-associated proteins A(SP-A),B(SP-B),C(SP-C),and D(SP-D)1.The truncations and/or modifications of bovine extremely hydrophobic surfactant protein C have been systematically analyzed by LC-MS/MS based on the database retrieval.The detected molecular masses of SP-C indicated diversity compared to the calculated molecular masses using the published amino acid sequences2.The amino acid sequence of SP-B was analyzed by LC-MS/MS in its tryptic peptide forms3.The amino acid sequence of SP-C was analyzed by LC-MS/MS in its tryptic peptide and intact forms.Bovine SP-B exists as dimers which are consistent with the observed mass transformation detected by LC-Q-TOF-MS based on natural and reduction of the SP-B dimer using 50 mM dithiothreitol.Analysis of the pulmonary surfactant-associated proteins B and C demonstrates several characteristics.(1)The modifications of SP-C observed contain one to three palmitoyl moieties4,which contains two thioester-linked palmitoyl groups and/or palmitoyl chain amide-bound to lysine.SP-C also exists with N-terminal acetylation,methionine oxidation and C-terminal methylated simultaneously or asynchronously.(2)The molecular weight of monomer and dimeric SP-B is determined by LC-Q-TOF-MS with dithiothreitol treatment or not.(3)Reduction treatment has no effect on the conformations of SP-C,which indicates that none of polymer existed in it.(4)Several dozens of polypeptide with different molecular weight were retrieved by software of PD 1.4 edition,which are coded by the same gene.In conclusion,this proposal offers a sensitive means of identifying modifications and truncations of SP-B or SP-C.It might also useful and accurate for analysis of other modified polypeptides,like lipopeptide or glycopeptide.