PHASE-BEHAVIOR AND ARRANGEMENT OF MOLECULAR-SPECIES IN MIXTURES OF A MIXED CHAIN AND A SYMMETRICAL PHOSPHATIDYLETHANOLAMINE IN THE GEL AND FLUID PHASES
Mm. Harrison et al., PHASE-BEHAVIOR AND ARRANGEMENT OF MOLECULAR-SPECIES IN MIXTURES OF A MIXED CHAIN AND A SYMMETRICAL PHOSPHATIDYLETHANOLAMINE IN THE GEL AND FLUID PHASES, Biochimica et biophysica acta, 1149(2), 1993, pp. 292-298
1-Octadecanoyl, 2-decanoylphosphatidylethanolamine (C(18:0)C(10:0)PE)
has been reported to exhibit mixed interdigitated gel-phase packing of
the phospholipid acyl chains (Mason, J.T. and Stephenson, F.A. (1990)
Biochemistry 29, 590-598). In contrast, ditetradecanoylphosphatidylet
hanolamine (C(14:0)C(14:0)PE) packs without significant interdigitatio
n of the phospholipid acyl chains across the bilayer center. In this r
eport, the gel-fluid transition temperatures of (18:0)C(10:0)PE and C(
14:0)C(14:0)PE in multilamellar dispersions were determined by fluores
cence anisotropy of cis-parinaric acid and trans-parinaric acid with a
descending temperature scan rate of 0.67-degrees-C/min. The transitio
n mid-points detected for C(18:0)C(10:0)PE with cis-parinaric acid wer
e 19-degrees-C in water, 18-degrees-C at pH 8.1, and 14-degrees-C at p
H 10. The phase diagram for C(14:0)C(14:0)PE and C(18:0)C(10:0)PE at p
H 10 suggests complete mixing in the fluid phase and considerable immi
scibility in the gel phase. Cross-linking of equimolar mixtures of C(1
4:0)C(14:0)PE and C(18:0)C(10:0)PE with dimethylsuberimidate at pH 10
revealed a random arrangement of the two species in the fluid phase, c
onfirming the notion that C(18:0)C(10:0)PE and C(14:0)C(14:0)PE are mi
scible in the fluid phase, as determined from the phase diagram. In co
ntrast, cross-linking of the equimolar mixture of C(18:0)C(10:0)PE and
C(14:0)C(14:0)PE in the gel phase at 0-degrees-C revealed a non-rando
m arrangement, demonstrating and confirming immiscibility in the gel p
hase.