Iodothyronine–phospholipid interactions in the lipid gel phase probed by Raman spectral markers

•We studied the structural effects of T3 and T4 on a DPPC membrane in the gel phase.•Spectral changes demonstrate that both hormones penetrate the ordered bilayer.•Interdigitation and increase in the gauche content occur upon hormone incorporation.

A better understanding of the structural effects induced by thyroid hormones in model membranes is attained by Raman spectroscopy. The interactions of T3 and T4 with multilamellar vesicles of dipalmytoylphosphatidylcholine (DPPC) in the gel phase are characterized by analyzing the spectral behavior of the C–H and C–C stretching vibrations of the acyl chains. The spectra evidence an increase in the relative number of gauche   conformation, which indicates the hormones are able to penetrate into the hydrophobic region of the bilayer and partially alter the lipid structure. In addition, the density packing of the acyl chains appears increased and the rotational mobility of the terminal methylene groups is slightly reduced in the iodothyronine/DPPC mixtures. These effects are interpreted in terms of the transition to an interdigitated phase due to the hormone incorporation to the membrane. The polar heads of the lipids also interact with the hormone, as evidenced by the PO2- symmetric stretching band.

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