Hiho,
The Professor told us that there is an asymmetrical distribution of (among others) phosphatidylcholine, -serine, -inositol, -ethanolamine, sphingomyeline between the cytosolic leaflet and the exoplasmatic leaflet.
Indeed, -choline is almost exclusively found in the outer leaflet; -serine is, in a steady state cell, exclusive to the inner leaflet; -inositol and -ethanolamine are exclusive to the cytosolic leaflet. Choline is found in the inner leaflet only as an intermediate, that is, it is on its way to being flipped over to the outer leaflet.
Next, the Professor tells us that while the plasmamembrane has an asymmetrical distribution, the endoplasmatic reticulum membrane has a symmetrical distribution of the phospholipids.
This is in contrast with the textbook: it says that the endomembrane has a translocator for -choline, but not for anything else: therefore, the inner leaflet of the endomembrane exists without the presence of -serine, -inositol, -ethanolamine
Can anybody tell me more about the inner- and outer leaflet of the endomembrane?
Rik