SYNTHESIS AND INTRACELLULAR-TRANSPORT OF AMINOGLYCEROPHOSPHOLIPIDS INPERMEABILIZED CELLS OF THE YEAST, SACCHAROMYCES-CEREVISIAE

The sequence of biosynthetic steps from phosphatidylserine to phosphat idylethanolamine (via decarboxylation) and then phosphatidylcholine (v ia methylation) is linked to the intracellular transport of these amin o-glycerophospholipids. Using a [H-3]serine precursor and permeabilize d yeast cells, it is possible to follow the synthesis of each of the a minoglycerophospholipids and examine the requirements for their intero rganelle transport. This experimental approach reveals that in permeab ilized cells newly synthesized phosphatidylserine is readily transloca ted to the locus of phosphatidylserine decarboxylase 1 in the mitochon dria but not to the locus of phosphatidylserine decarboxylase 2 in the Gels and vacuoles. Phosphatidylserine transport to the mitochondria i s ATP independent and exhibits no requirements for cytosolic factors. The phosphatidylethanolamine formed in the mitochondria is exported to the locus of the methyltransferases (principally the endoplasmic reti culum) and converted to phosphatidylcholine , The export of phosphatid ylethanolamine requires ATP but not any other cytosolic factors and is not obligately coupled to methyltransferase activity. The above descr ibed lipid transport reactions also occur in permeabilized cells that have been disrupted by homogenization, indicating that the processes a re extremely efficient and may be dependent upon stable structural ele ments between organelles.