Among the pigments found in nature, carotenoids are the most widespread and important ones, found mainly in algae, photosynthetic bacteria and plants. The pattern of alternating single and double bonds in the polyene backbone of carotenoids allows them to absorb energy excess from other molecules. This structure is also responsible for the characteristic yellow, orange or red colors. Carotenoids can modulate the thylakoid membrane fluidity that should be considered as an adaptive mechanism to unstable temperatures of the environment. This experiment was planned to elucidate the relationship between the structure of carotenes and their effect on the molecular dynamics of membranes. We have investigated the influence of the carotenes b-carotene (CAR) and lycopene (LYC) on phase transition temperature (Tm) behavior of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) large unilamellar vesicles (LUV) by means of light scattering (detection at 250 nm) in function of the heating or cooling process (from 15^o to 30^oC). The beginning and ending transition temperatures were determined as well as their corresponding transition region. LUV were obtained by CH₂Cl₂ injection into aqueous solution (20mM TRIS-HCl, pH 7,2). The suspension was passed through two polycarbonate filters in a mini-extruder. The results showed that CAR and LYC decrease the transition cooperation related to the phase transition region increasing, but in relationship to Tm data were not significantly different (p<0.05). The hydrodynamic radius of the vesicles was determined by quasi-elastic light scattering (QELS). It showed a reduction of approximately 36% due to the incorporation of both carotenes. This effect on the molecular dynamic of mimetic membrane should probably be a new property of carotenes in compacting lipid systems and, consequently, changing in permeation of reactive oxygen species (ERO). In addition, several experiments should be performed to determine diffusion coefficient of ERO that confirm this new property.
Supported by: FAPESP