For example PS synthase, PI synthase, and diacylglycerol cholinephosphotransferase are enriched in regions of the ER that are closely apposed to mitochondria or the plasma membrane.
Lipids produced at MCSs may be present at high concentrations at these sites, increasing the likelihood that the lipid will be transferred by an LTP to the apposing membrane(Figure 1).
Indeed, it has been shown that newly synthesized PS is preferentially transferred from the ER to mitochondria where it is converted to phosphatidylethanolamine (PE).
It may also be possible that lipidsynthesizing enzymes at MCSs hand lipids directly to LTPs, facilitating lipid transfer.
Thus, there could be some form of substrate channeling from lipid synthesizing enzymes to LTPs at contact sites.
Substrate channeling is the process by which the product of one enzyme is passed directly to a second enzyme.