Journal of Lipid Research, Vol 37, 2125-2135, Copyright © 1996 by Lipid Research, Inc.
Effect of phospholipids on the structure of Triatoma infestans lipophorin studied by fluorescence methods
OJ Rimoldi, HA Garda and RR Brenner
Instituto de Investigaciones Biocuimicas de la Plata (INIBIOLP), CONICET-UNLP, Facultad de, Ciencias Medicas, Argentina.
To study the role of phospholipids in the lipophorin structure, they were
removed by phospholipase A2 treatment. Fluorescence lifetimes and
accessibility to acrylamide quenching of different diphenylhexatrienyl
derivatives, which were used as analogues of the different lipid
components, indicate a surface localization of phospholipids and a
distribution of diacylglycerols between the core and the surface, the
surface fraction being increased by the phospholipase A2 treatment. The
rotational behavior of these probes, studied by differential polarized
phase fluorescence, indicates a high lipid order not only in the surface
layer where phospholipids are located, but also in the core occupied by
diacylglycerols and hydrocarbons. Phospholipid depletion increases the
order only in the external region of the surface layer. Energy transfer
from apolipoprotein tryptophan residues to several fluorescent acceptors
indicates that phospholipid depletion produces a re-accommodation of the
apoproteins. A decreased mobility of the water in the interfacial region is
also produced by the phospholipase A2 treatment as it is reported by the
fluorescence of 6-lauroyl-2- dimethylaminonaphthalene. This work shows that
phospholipase A2 treatment of T. infestans lipophorin results in stable
particles with an increased diacylglycerol to phospholipid ratio in the
surface lipid layer. The modified particles are possibly stabilized by a
conformational change in the apolipoproteins.
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