The effect of zeaxanthin on the thickness of dimyristoylphosphatidylcholine bilayer: X-ray diffraction study

Multilayers of dimyristoylphosphatidylcholine (DMPC) modified with a carotenoid pigment zeaxanthin were analyzed by means of small-angle X-ray diffractometry. The results are discussed in terms of the superlattice theory developed recently for metallic multilayers. Inclusion of zeaxanthin to a DMPC bilayer increases thickness of the hydrophobic core by about 3 Å in the whole lipid-pigment miscibility range. The thickness increases very sharply as pigment concentration approaches the threshold of miscibility. Zeaxanthin aggregation within a layer causes further changes in the thickness of the membrane: a local decrease followed by a gradual rise.