Lipid acceptor protein

Increased synthesis of lipid acceptor proteins is part of the mechanism of fat accumulation in the hepatocyte. 

Lack of formation of lipid acceptor protein in the liver leads to hepatic steatosis. 

Studies of the effect of permeant s size on the translational diffusion in membranes suggest that a free-volume model is appropriate for the description of diffusion processes in the bilayers [93]. The dynamic motion of the chains of the membrane lipids and proteins may result in the formation of transient pockets of free volume or cavities into which a permeant molecule can enter. Diffusion occurs when a permeant jumps from a donor to an acceptor cavity. Results from recent molecular dynamics simulations suggest that the free volume transport mechanism is more likely to be operative in the core of the bilayer [84]. In the more ordered region of the bilayer, a kink shift diffusion mechanism is more likely to occur [84,94]. Kinks may be pictured as dynamic structural defects representing small, mobile free volumes in the hydrocarbon phase of the membrane, i.e., conformational kink g tg ) isomers of the hydrocarbon chains resulting from thermal motion [52] (Fig. 8). Small molecules can enter the small free volumes of the kinks and migrate across the membrane together with the kinks. 

The transfer of phospholipids between mitochondria and microsomes in vitro was first used to measure the activity of lipid transfer proteins (Wirtz and Zilversmit, 1968). In this assay, isolated mitochondria and microsomes are incubated with an appropriate amount of transfer protein. Either particle may be radiolabeled and serve as the donor particle. The exchange reaction is terminated by sedimenting the mitochondria by centrifugation. The change in the radioactivity of either the donor or acceptor particles can be used to calculate the lipid transfer activity. 

The incorporation of 3H-NeuNAc into endogenous acceptors of the two primary retina fractions is shown in Table 1. The labelling of lipids and proteins in total ROS free membranes was about six fold greater than the labelling of lipids and proteins found in total ROS membranes. Subfractionation of the ROS free membranes in a sucrose density gradient resulted in the isolation of membranes with different activities for the incorporation of NeuNAc. The highest activity was in subfraction Pla (Table 2). The incorporation of radioactivity into lipids paralleled the labelling of proteins in all the subfractions, from the more active Pla to the less active... 

Additional roles for lipid transfer proteins have been assumed regulation of the acyl-CoA pool within the cytosol and participation in the biosynthesis of llnolenic acid via the cooperative pathway involving the plastids and the endoplasmic reticulum (Dubacq et al., 1984). It has been showed that the chloroplast envelope is a efficient membrane acceptor for phosphatidylcholine molecules transported by lipid transfer proteins ( Miquel et al., 1987). Also, by transporting linoleoy 1-phosphatidylcholine towards chloroplasts by lipid transfer proteins, Ohnishi and Yamada (1982) observed a synthesis of linolenoyl- monogalactosyldiacylglycerol. A phospholipase activity... 

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