Biology Reference
In-Depth Information
PC Lipid Vesicle
Mitochondrion
32
P-PC
unlabeled-PC
discard
INCUBATE
T = X
new PLEP
new Mitochondria
FIGURE 9.20
Use of a PLEP
(PC)
to determine the inherent rate of flip-flop for PC in a protein-free lipid bilayer
(liposome). The PCs are either
32
P-PC (black head group) or non-labeled mitochondrial PC (white head group).
ten times greater than for the homologous PC derivative. They also reported that the flip-flop
rate for PA increased 500 times when the solution pHwas decreased from 7.4 to 4.0. At pH 4.0
the net negative charge on PA is much reduced compared to pH 7.4. Finally, Middelkoop et al.
[35]
reported the effect of acyl chain composition on the flip-flop rate of various PCs (16:0,16:0
PC
16:0, 20:4 PC). They reported that for erythrocytes at 37
C
flip-flop half-lives decreased with increasing number of double bonds.
Another way of looking at lipid flip-flop is to determine the effect of the bilayer hydro-
phobic environment (acyl chain components) on the flip-flop of a single lipid species.
Armstrong et al.
[36]
measured flip-flop rates for the fluorescent phospholipid NBD-PE by
<
18:1,18:1 PC
<
16:0,18:2 PC
<
