2Chapter 4 Transport of Carotenoids by a Carotenoid-Binding Protein in the Silkworm
The concentrations and types of carotenoids in animals differ substantially among tissues. They occasionally undergo signi cant chemical transformations, and they can be a critical factor for survival. For example, the green larvae of the swallowtail butter y, Papilio xuthus, become green pupae when the larvae pupate on green twigs of plants. The green pupal cuticles contain b-carotene and lutein (Ohnishi 1959). However, if pupation takes place on dead branches, brown pupae are usually produced, likely in response to odorant stimuli (Hidaka 1961). Neither b-carotene nor lutein have been detected in the brown pupal cuticle, but papilioerythrin and an astaxanthin-like carotenoid, presumably canthaxanthin, were found (Ohnishi 1959, Harashima et al. 1972). The concentrations and types of carotenoids in the pupae of P. xuthus vary signi cantly among hemolymph, fat bodies, and cuticles (Harashima et al. 1972). A protective role of the color of the cuticle has been proposed based on an experiment with fowl as the predator (Hidaka et al. 1959), which suggested that the carotenoid composition is a critical factor for survival. Carotenoid composition is also signi cant in human medicine. For example, high macular levels of lutein and zeaxanthin are associated with a decreased risk of age-related macular degeneration (Loane et al. 2008), the main cause of blindness in the developed world.