Purification of a basic phospholipid transfer protein from maize seedlings

A phospholipid transfer protein has been purified 125-fold from maize seedlings. The successive steps of purification comprised gel filtration on Sephadex G-75, DEAE- and CM-chromatography and chromatofocusing. The homogeneity of the protein was determined by polyacrylamide gel electrophoresis with and without SDS and by isoelectric focusing. The protein has an apparent molecular weight of 20000, as estimated from SDS electrophoresis, and an isoelectric point of 8.8 ± 0.2. The amino acid composition of the protein is characterized by a high content of alanine, glycine, cysteine and serine and a small amount of lysine. A molecular weight of 14058 was calculated from this amino acid composition. The protein only loses 25% of its activity after 5 min heating at 95°C. The purified protein is able to transfer phosphatidylcholine, phosphatidylinositol and phosphatidylethanolamine between liposomes and mitochondria at the rates of, respectively, 100, 56 and 1.6. After incubation of the purified protein with [³H]phosphatidylcholine, a labelled phosphatidylcholine-protein complex was obtained after chromatofocusing. This suggests that the protein acts by carrying phosphatidylcholine from a membrane toward another one.