ABSTRACT
This chapter presents what is known about the spontaneous transfer of phospholipids between membranes and the knowledge about a few intracellular lipid transfer proteins. It discusses the spontaneous mechanism of transbilayer movement, followed by the knowledge of membrane proteins that facilitate and even drive phospholipid movement. Implicit in being able to measure the rate of protein-stimulated phospholipid transfer is the ability to measure the spontaneous rate in the absence of protein. Spectroscopic and other physical methods can be used to monitor continuously the transfer of phospholipids between membranes without separating donors and acceptors. Considering the transfer of phospholipids between two populations of stable membranes, bilayers, or lipid-rich particles that do not fuse, the rate of spontaneous transport is inversely dependent on the number and length of the acyl chains in the phospholipid molecule. R. Homan and H. J. Pownall used changes in pyrene eximer fluorescence to measure the intermembrane and transbilayer transfer of pyrene-labeled phospholipids.
