Arg. Dibble et al., PARTITIONING OF GRAMICIDIN A' BETWEEN COEXISTING FLUID AND GEL PHOSPHOLIPID PHASES, Biochimica et biophysica acta, 1153(2), 1993, pp. 155-162
The partitioning behavior of gramicidin A' was investigated in four bi
nary phospholipid mixtures with coexisting fluid and gel phases. The r
atio of the equilibrium peptide concentration in the fluid phase to th
at in the gel phase (i.e., the partition coefficient, K-p) was determi
ned by analysis of the quenching of gramicidin A' tryptophanyl fluores
cence by a spin-labeled phosphatidylcholine. The partition coefficient
was used as a measure of the relative solubility of gramicidin A' in
the four types of gel phases analyzed. The composition of the gel phas
e was entirely Ca(dioleoylphosphatidylserine), (Ca(di18:1-PS)(2)), or
was rich in either distearoylphosphatidylcholine (di18:0-PC), dipalmit
oylphosphatidylcholine (di16:0-PC), or dimyristoylphosphatidylcholine
(di14:0-PC). Except in the last case, the gel phase was depleted of gr
amicidin A': K-p similar to 30 when the gel phase was Ca(di18:1-PS)(2)
or di18:0-PC-rich, K-p similar to 10 when the gel phase was di16:0-PC
-rich, and K-p similar to 1 when the gel phase was di14:0-PC-rich. The
hydrophobic mismatch between the length of gramicidin A' and the leng
th of the phospholipid acyl chains in the bulk gel phase is greatest w
ith di18:1-PS and di18:0-PC, intermediate with di16:0-PC, and least wi
th di14:0-PC. The K-p measurements presented here are consistent with
increasing solubility of gramicidin A' in the gel phase with decreasin
g hydrophobic mismatch.