Properties of a non-specific phospholipid-transfer protein purified from rat lung

The present report describes the purification and characterization of a non-specific phospholipid-transfer protein from rat lung. The protein is the major phospholipid-transfer protein in lung which transfers phosphatidylcholine. The transfer protein was purified 1200-fold, with a final yield of 3%. The activity of the protein was monitored by measuring the transfer of [14C]phosphatidylcholine from radioactively labeled liposomes to mitochondria. The purified proteins transfers phosphatidylcholine, phosphatidylinositol, phosphatidylserine and phosphatidylethanolamine from radioactively labeled microsomes to either mitochondria or liposomes. The transfer of each phospholipid is proportional to its content in the donor membrane. The protein was purified from a pH 5.1 supernatant preparation by fractionation on DEAE-cellulose, Sephadex G-75 and hydroxyapatite. The molecular weight of the purified protein was estimated as 35 000 by SDS-polyacrylamide gel electrophoresis. The amino acid analysis revealed a high content of glutamic acid (including glutamine) and glycine. The specificity of the purified protein for transfer of phospholipids suggests that it may be the phospholipid-transfer activity which is highly enriched in isolated type II alveolar cells of rat lung.