Raman spectroscopy demonstrated that (1) in pure lipid membranes (dihexadecylphosphatidic acid or phosphatidylcholines), the lipid chains are mainly in an all-trans conformation in the ordered membrane phase, and in the fluid phase, lipid chains contain all-trans segments of 11 or 8 C atoms, resp.; (2) in charged membranes (dimyristoylmethylphosphatidic acid at pH 9), in addn. to a phase transition shift from 46 to 32 Deg, the lipid chain conformation is disordered, and the disordering effect is concd. at the chain ends; and (3) the presence of proteins (melittin) in dimyrisytoylphosphatidylcholine membranes decreases the conformational order below the phase transition temp., with a slight increase in the conformational order being obsd. in the fluid phase. [on SciFinder (R)]