INFLUENCE OF CHOLESTEROL AND BETA-SITOSTEROL ON THE DYNAMIC BEHAVIOR OF DPPC AS DETECTED BY TMA-DPH AND PYRPC FLUORESCENCE - A FLUORESCENCELIFETIME DISTRIBUTION AND TIME-RESOLVED ANISOTROPY STUDY
C. Bernsdorff et al., INFLUENCE OF CHOLESTEROL AND BETA-SITOSTEROL ON THE DYNAMIC BEHAVIOR OF DPPC AS DETECTED BY TMA-DPH AND PYRPC FLUORESCENCE - A FLUORESCENCELIFETIME DISTRIBUTION AND TIME-RESOLVED ANISOTROPY STUDY, Berichte der Bunsengesellschaft fur Physikalische Chemie, 99(12), 1995, pp. 1479-1488
Citations number
64
Categorie Soggetti
Chemistry Physical
Journal title
Berichte der Bunsengesellschaft fur Physikalische Chemie
Fluorescence lifetime and time-resolved anisotropy measurements on rim
ethylammonium-phenyl)-6-phenyl-1,3,5-hexatriene (TMA-DPH) and oyl-2-[1
0-(1-pyrenyl)decanoyl]-phosphatidylcholine (PyrPC) in lipid vesicles o
f 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine (DPPC) with and wit
hout cholesterol and beta-sitosterol, using multifrequency cross-corre
lation phase fluorometry, are presented. We used TMA-DPH and PyrPC as
fluorescence probe for detecting rotational dynamics. Contrary to TMA-
DPH, which is tethered to the bilayer interface and therefore detects
wobbling rotational dynamics in the interfacial and headgroup region,
PyrPC senses the deeper acyl chain dynamics of the lipid bilayer. We h
ave investigated the influence of sterol structure on the lipid dynami
cs. The experiments were carried out at two temperatures, one below an
d one above the main phase transition temperature of DPPC. Data were a
nalyzed in terms of Lorentzian distribution functions for the fluoresc
ence lifetime results and in terms of hindered rotation for the time-r
esolved anisotropy results. We noticed, that addition of cholesterol a
nd beta-sitosterol results in a distinct increase in average fluoresce
nce lifetime of TMA-DPH in both lipid phases. The rotational rates of
TMA-DPH depolarizing motions are only modestly increased in going from
the gel to the liquid-crystalline phase of DPPC. However, a marked in
crease in the contribution of fast rotational motions of TMA-DPH is fo
und as the temperature is increased through the main transition. No si
gnificant differences in rotational rates of TMA-DPH exist between sam
ples with embedded cholesterol or beta-sitosterol at T=55 degrees C. T
he rotational rate of TMA-DPH in the gel state of the lipid bilayer at
T=35 degrees C is slightly larger in the case of beta-sitosterol, how
ever. Cholesterol and beta-sitosterol, then, have a similar effect on
the contribution of fast rotational dynamics in the interfacial region
of the bilayer. It decreases about 40% upon addition of 50 mol-% ster
ol. The incorporation of either sterol into DPPC vesicles leads to an
increase in fluorescence lifetime of PyrPC in both lipid phases. The r
otational rates of PyrPC in the bilayer are an order of magnitude smal
ler than those of TMA-DPH. Also the contributions of fast rotational m
otions significantly differ for the two fluorophores. The motional fre
edom in the deeper acyl chain region of DPPC in its fluid-like state a
t T=55 degrees C is scarcely affected by addition of either sterol. Ho
wever, differences in the rotational rates of the two sterols are obse
rved for high sterol concentrations.