PHOSPHATIDYLCHOLINE MOLECULAR-SPECIES OF CALF LUNG SURFACTANT

This paper reports the detailed composition of molecular species of th e phosphatidylcholines (PCs) in pulmonary surfactant from calves. PC i solated by thin-layer chromatography (TLC) was converted to benzoylate d diradyl glyceride derivatives, which were separated by TLC according to linkage group. Quantification of linkage groups by analysis of tot al fatty acid content demonstrated that surfactant PC contained 97.2% diacyl, 2.4% alkyl-acyl, and 0.4% alkenyl-acyl compounds. The diacyl a nd alkyl-acyl diglyceride derivatives were separated into individual m olecular species by high-performance liquid chromatography. Four major species constituted 87% of the diacyl compounds. Dipalmitoyl phosphat idylcholine (DPPC) was the most abundant constituent, contributing 41% of the total PC. A second disaturated species, palmitoyl-myristoyl ph osphatidylcholine (PMPC), also contributed an additional 12% of total PC. At least 65% of PMPC occurred as the 1-palmitoyl-2-myristoyl isome r, which has a lower melting point than the 1-myristoyl-2-palmitoyl co mpound. These results show that most of pulmonary surfactant PC is a r elatively simple mixture, that numerous minor compounds are present in small but possibly important amounts, and that in surfactant from cal ves, the widely reported estimate that DPPC constitutes 60% of surfact ant PC is too large by 50%.