Acyl Transfer Reactions Associated with Cis Golgi Apparatus

Abstract

Recent work in our laboratory involving cell-free lipid transfer from transitional endoplasmic reticulum (ER) to Golgi apparatus has shown a latent phospholipase A activity localized in the cis Golgi of rat liver (Moreau 1991). Subsequently, phosphatidylethanolamine (PE) was shown to be an important component of ER to Golgi transport vesicles. Because PE has a small hydrophilic head group and a large hydrophobic tail, it has a conical shape which is very conducive to Hexagonal II phase structure formation. The possibility that we examined was that the lysophosphatidylcholine (lysoPC), formed by the phospholipase A activity, could interact with the PE to destabilize the Hexagonal II phase and form a bilayer. However, because levels of PE decrease through the Golgi stacks, the presence of lysoPC will then destabilize the bilayer structure. To retain a stabile bilayer structure, the lysoPC must be removed. This can be accomplished in two ways: 1) degradation by a Golgi lysophospholipid phospholipase or 2) reacylation by a Golgi acyl-CoA:lysoPC acyltransferase activity. The reacylation of Golgi apparatus lysoPC via the Lands pathway (Lands 1976) was investigated.