Effect of beta-carotene on structural and dynamic properties of model phosphatidylcholine membranes. I. An EPR spin label study.

The influence of beta-carotene on structural and dynamic properties of model membranes (multilamellar liposomes) prepared of dipalmitoylphosphatidylcholine was investigated. It was found that beta-carotene: (1) decreases order within crystalline state of the membrane; the effect of beta-carotene was more pronounced than in the case of the polar carotenoid, lutein, as revealed by means of spin label EPR; (2) increases penetration, stronger than lutein, of apolar molecules into the membrane as indicated by greater partition coefficient of 5-doxyldecane; (3) increases correlation times tau B tau C stronger than lutein. In all cases the effect of beta-carotene on a membrane was more pronounced at crystalline state than at fluid state. On this basis a hypothesis is proposed that beta-carotene plays a physiological function in the fluidization of chloroplast membranes in a chilling stress to the photosynthetic apparatus.