Phosphatidylserine delivery to endoplasmic reticulum-derived vesicles of plant cells depends on two biosynthetic pathways

Vesicles formed from endoplasmic reticulum (ER) by a cell-free system of le ek cells (Allium porrum) are enriched in phosphatidylserine (PS), especiall y species containing very long chain fatty acids (VLCFA, at least 20 carbon atoms). In plant cells, PS is formed either by PS synthase or the serine e xchange enzyme, although it is not known which pathway(s) contribute(s) to PS delivery in the ER-derived vesicles (EV), nor to what extent this occurs . Taking advantage of a cell-free system, we have shown that PS enrichment originates mainly from the serine exchange enzyme which is the only pathway that synthesizes the VLCFA-PS species. On the other hand, both enzymes syn thesize PS with long chain fatty acids (up to 18 carbon atoms), but these s pecies are given to the EV by PS synthase, (C) 2001 Federation of European Biochemical Societies, Published by Elsevier Science B.V. All rights reserv ed.