Lipids in Membranes - Membrane Biophysics, Biological and Medical Physics, Biomedical Engineering - page 44

800

12

600

8

400

4

200

0 0

20 30 40 50 60 70 40 50 60 70

T / 0 C T / 0 C

Fig. 3.8 DSC heating thermograms of DEPE dispersions without or with Alm ( top to bottom 0,
0.15, 0.2, 0.22, 0.25, 0.3, 0.5, 0.55, 0.6, 0.75, 1.0, respectively mole% Alm in DEPE) [ 1 ]. The left
panel covers the whole temperature range (20-75 ◦ C) while the right panel covers only the range
showing a L α / H II phase transition

to Alm. With a further increase of the AMP level (Alm-lipid ratio between 0.2
and 0.3%) with GS-lipid ratio between 0.136 and 0.34%, T H modestly increases.
It slightly decreases again with increasing the Alm level (Alm-lipid ratio between
0.3 and 0.5%) but slightly increases with an increasing GS level (GS-lipid ratio over
0.34). At a still higher Alm level (AMP-lipid ratio over 0.5%), T H first decreases
sharply (between 0.5 and 0.6%) and then continues to decrease modestly; whereas
at still higher GS levels, T H continues to increase modestly. An inverse relation
between Alm/GS-induced changes of T H and co-operativity of the L

/ H II transition

α

is also noticed. ) 12 , at a ratio of under 0.5% with respect to lipid concentration,

negligibly decreases T H , although at ultra-low concentrations,

( LA

) 12 causes T H
to also decrease further; however, the drop is clearly less, and much less than that
for Alm and GS. Interestingly, at a low level, we observe a trend showing a higher
drop in T H due to the effects of an even lower level of AMP, with its being more
non-transmembrane. A modest reduction in T m ,

( LA

H , co-operativity etc., is detected

at the investigated range of the ) 12 concentration.

In a binary mixture of Alm (fixed 0.5%) and different GS/(LA) 12 concentrations
in DEPE dispersions, the changes in T m ,

( LA

H and co-operativity almost follow (albeit
with slightly higher effects) that of independent GS/(LA) 12 effects on the L β / L α tran-
sition. In the L α / H II transition, 0.5%Alm alone reduces T H and H , but changes the

co-operativity only modestly. With an increasing GS/(LA) 12 ratio, the L α / H II tran-
sition initially broadens, with a decreasing co-operativity at low GS or (LA) 12 /lipid
ratios. However, with increasing ratios, the L α / H II transition gradually regains
co-operativity, and at a very high GS/(LA) 12 level, the transition becomes weaker