Acyl chain specificity of phosphatidylcholine transfer protein from bovine liver.

The specificity of bovine liver phosphatidylcholine transfer protein for various phosphatidylcholine (PC) molecular species was examined at 37 degrees C. The amount of transfer between donor and acceptor vesicles of defined phospholipid composition was determined. Protein-mediated transfer between vesicles of long chain, fluid phase PCs (di-16:1 PC, di-17:1 PC, di-18:1 PC, di-18:2 PC, or egg PC) was markedly higher than transfer between vesicles of solid phase or short chain, fluid phase PCs (di-18:0 PC, di-16:0 PC, or di-14:0 PC). When di-14:0 PC and di-18:1 PC were present in the same vesicle, protein-mediated transfer of di-18:1 PC was still higher, indicating that the protein's specificity toward long chain, fluid phase PCs is based on true acyl chain structure preference rather than a bulk phase physical property of the longer chain PCs. The effect of adding a third type of vesicle to a system which consisted of transfer protein, donor vesicles, and acceptor vesicles was investigated. Addition of solid phase PC vesicles does not affect transfer of the well transferred species, while addition of the poorly transferred short chain, fluid phase PCs does inhibit transfer. These results suggest that the transfer protein has the ability to bind to any fluid phase PC vesicle, although it preferentially extracts and transfers long chain, fluid phase PCs.