Purification and characterization of lipid transfer protein(s) from human lipoprotein-deficient plasma

Lipid transfer activities from human plasma have been characterized to determine whether triglyceride and cholesteryl ester transfer proteins are identical. After sequential purification by phenyl-Sepharose, CM-cellulose, chromatofocusing, and gel filtration, both triglyceride and cholesteryl ester transfer activities were purified approximately 15,000-fold compared to lipoprotein-deficient plasma, with a 14% recovery of both transfer activities. The gel filtration fraction showed two bands, Mr 58,300 and 66,400, as determined by electrophoresis in sodium dodecyl sulfate. Two samples, each containing predominately one of the two bands, were obtained by selectively combining the eluates from the gel filtration column. The specific activities of triglyceride and cholesteryl ester transfer promoted by the larger protein were within 10% of those for the smaller protein. The relative rates of transfer for cholesteryl ester, triglyceride, retinyl ester, and cholesteryl ether for each fraction were the same. The transfer of triglyceride by either the large or small molecular weight component was almost completely inhibited by mercurial compounds, whereas cholesteryl ester transfer was relatively unaffected. We conclude that triglyceride and cholesteryl ester are transferred by the same plasma protein(s).