Journal of Lipid Research, Vol 37, 2305-2309, Copyright © 1996 by Lipid Research, Inc.
Differential scanning calorimetry study of the influence of phospholipid analogs with a carbonyl-terminated sn-2 chain on the interdigitated phases formed by 1-stearoyl-2-capryl-sn-glycero-3- phosphatidylcholine (C18:C10-PC)
S Ali and R Bittman
Department of Chemistry and Biochemistry, Queens College of The City University of New York, Flushing 11367-1597, USA.
Synthetic glycerophosphocholines with highly asymmetric chain lengths form
interdigitated bilayers in the gel phase. In nature, phospholipids with one
hydrocarbon chain approximately twice as long as the other can arise from
the autooxidation of unsaturated linkages in the acyl chain, and thus the
oxidation products would contain a carbonyl group at the chain terminus. In
this study, we have investigated the thermotropic behavior of bilayers
prepared from mixtures of the well-studied, mixed- chain phospholipid,
1-stearoyl-2-capryl-sn-glycero-3-phosphocholine (C18:C10-PC, 1), with
synthetic 1-stearoyl-2-acyl-sn-glycero-3- phosphocholines in which the sn-2
chain is approximately one-half the length of the sn-1 chain and contains a
C==O group near the omega terminus. Phase diagrams of binary mixtures of 1
with a chain-terminal ketone-PC analog (2) or with a chain-terminal
ester-PC analog (3) in excess water exhibited gel-phase immiscibility over
a wide compositional range, but miscibility in the liquid-crystalline
phase. However, 1 was completely miscible with C18:C10:1 delta 10-PC
(compound 4), which bears a chain-terminal carbon-carbon double bond, in
both the gel and liquid-crystalline phases. The calorimetric data suggest
that phosphatidylcholines (PC) with carbonyl-terminated chains, which can
be produced by autooxidation of naturally abundant 1-saturated-2-
unsaturated phospholipids such as 1-stearoyl-2-oleoyl-PC, may not form the
normal triple-chain mixed interdigitated structure characteristic of
hydrocarbon-terminated PCs in gel-phase bilayers.