1: Biochemistry  1981 Jul 21;20(15):4257-62 

Effect of double bonds on the dynamic properties of the hydrocarbon region of
lecithin bilayers.

Stubbs CD, Kouyama T, Kinosita K Jr, Ikegami A.

The motional properties of the hydrophobic fluorescent probe
1,6-diphenyl-1,3,5-hexatriene have been assessed in liposomes of various
lecithins: dipalmitoyl-phosphatidylcholine (DPPC), dioleoylphosphatidylcholine,
1-palmitoyl-2-oleoylphosphatidylcholine (POPC), 1-
palmitoyl-2-linoleoylphosphatidylcholine (PLPC), and
1-palmitoyl-2-arachidonoylphosphatidylcholine (PAPC). The temperature dependence
of the steady-state fluorescence anisotropy was determined within the range of
10-50 degrees C. Nanosecond measurements were also made and the results analyzed
by a model of wobbling diffusion confined within a cone. In this treatment the
cone angle (theta c) obtained relates to the degree of order of the fatty acyl
chains, and the wobbling diffusion constant (Dw) relates to the rate of motion
of the hydrocarbon chains. Theta c was increased (order decreased) and Dw
increased (rate increased) for the first double bond (POPC) as compared to the
fully saturated DPPC. In all four unsaturated lecithins the temperature
dependences of theta c and Dw were similar: theta c increased by about 4-5
degrees, and Dw increased by a factor of 1.5 per 10 degrees C. DPPC in the
liquid-crystalline phase also showed a similar trend. The absolute values, on
the other hand, showed some differences: for theta c, DOPC (78 degrees at 37
degrees C) greater than PAPC (75 degrees) greater than POPC (70 degrees)
congruent to PLPC (69 degrees) greater than DPPC (20 degrees), and for Dw, PAPC
(0.28 ns-1) greater than DOPC (0.22 ns-1) congruent to PLPC (0.24 ns-1) greater
than POPC (0.21 ns-1) greater than DPPC (0.05 ns-1). The differences among the
unsaturated lecithins are relatively small suggesting that the first double bond
introduced into a lecithin plays the most important role at physiological
temperatures. In 1:1 mixtures of the disaturated lecithin, DPPC, with the
unsaturated lecithins, the temperature of the phase transition of the former was
lowered and broadened, by approximately the same amount, irrespective of the
differences in unsaturation.

PMID: 7284325 [PubMed - indexed for MEDLINE]