Long-Wavelength Absorbing Forms of Carotenoids

Abstract

It has been recognized that under certain conditions carotenoids with red-shifted absorption spectra for about 50 nm as compared with those in lipid solvents may occur. This shifting is believed to be due to interaction of pigment (mainly β-carotene) molecules with protein (e.g. Nishimura, Takamatsu, 1957, 1960, Ji et al., 1968, Vernon et al., 1969) or to aggregation that may take place in artificial lipid membranes (Litvin et al., 1965) as well as in aqueous organic solvents (Hager, 1970). A suspension of crystalline carotene also exhibits an absorption band within the range 520–530 nm (Shibata, 1956). It is still by no means clear, however, whether any particular pigments may occur in one or more LWAFs⁺ or whether they represent true natural forms or merely appear in vitro under appropriate conditions. We have undertaken studies in order to answer some of these questions. This communication deals with the comparison of the absorption spectrum of LWAF of β-carotene obtained by two different methods with that of the crystalline form. We have also attempted to find out whether other carotenoids may form LWAFs.