Astaxanthin, one of the dominant carotenoids in marine animals, showed both a strong quenching effect against singlet oxygen, and a strong scavenging effect against free radicals. These effects are considered to be defence mechanisms in the animals for attacking these active oxygen species. The activities of astaxanthin are approximately 10 times stronger than those of other carotenoids that were tested, namely zeaxanth in, lutein, tunaxanthin, canthaxanth in and , B carotene, and 100 times greater than those of a tocopherol. Astaxanthin also showed strong activity as an inhibitor of lipid peroxidation mediated by these active forms of oxygen. From these results, astaxanthin has the properties of a "SUPER VITAMIN E".

A carotenoid biosynthesis gene cluster for the production of astaxanthin was isolated from the marine bacterium Agrobacterium aurantiacum. This cluster contained five carotenogenic genes with the same orientation, which were designated crtW, crtZ, crtY, crtI, and crtB. The stop codons of individual crt genes except for crtB overlapped the start codons of the following crt genes. Escherichia coli transformants carrying the Erwinia uredovora carotenoid biosynthesis genes provide suitable substrates for carotenoid biosynthesis. The functions of the five crt genes of A. aurantiacum were determined through chromatographic and spectroscopic analyses of the pigments accumulated in some E. coli transformants carrying various combinations of the E. uredovora and A. aurantiacum carotenogenic genes. As a result, the astaxanthin biosynthetic pathway is proposed for the first time at the level of the biosynthesis genes. The crtW and crtZ gene products, which mediated the oxygenation reactions from ␤-carotene to astaxanthin, were found to have low substrate specificity. This allowed the production of many presumed intermediates of astaxanthin, i.e., adonixanthin, phoenicoxanthin (adonirubin), canthaxanthin, 3-hydroxyechinenone, and 3-hydroxyechinenone.During the last 6 years, significant advances have been made in our understanding of the genes coding for the enzymes involved in carotenoid biosynthesis. Many carotenoid biosynthesis genes have been cloned from various organisms, and their functions have been determined (3, 54, 62). Phytoene synthase genes, which mediate the formation of the first colorless carotenoid phytoene from geranylgeranyl PP i (GGPP) (11,46,55), have been isolated from the photosynthetic bacteria Rhodobacter species (5, 31), the nonphotosynthetic bacteria Erwinia species (4,45,60) and Thermus thermophilus (20), the cyanobacterium Synechococcus sp. strain PCC7942 (11), the fungus Neurospora crassa (57), and higher plants (7,50,51,58). Many genes involved in the desaturation (dehydrogenation) steps to convert phytoene to -carotene, neurosporene, or lycopene have also been obtained from the photosynthetic bacteria Rhodobacter species (5, 6, 31), the nonphotosynthetic bacteria Erwinia species (4, 45, 60) and Myxococcus xanthus (16), the cyanobacterium Synechococcus sp. strain PCC7942 (12), the fungi N. crassa (56) and Cercospora nicotianae (15), and higher plants (8,21,48). A second desaturase gene, which mediates the desaturation reaction from -carotene to lycopene, has been obtained from the cyanobacterium Anabaena sp. strain PCC7120 (33). The genes coding for lycopene cyclase, which catalyzes the formation of a cyclic carotenoid ␤-carotene from lycopene, have been isolated from the nonphotosynthetic bacteria Erwinia species (25, 45) and the cyanobacterium Synechococcus sp. strain PCC7942 (14).Among these organisms, the carotenoid biosynthesis genes of the yellow-pigmented nonphotosynthetic soil bacteria Erwinia uredovora (45) and Erwinia herbicola (4, 22, 60) have been used most frequently in the study o...

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Sesamin, a major lignan in sesame oil, is known to have many biological activities, especially protective effects against oxidative damage in the liver. As sesamin itself has no antioxidative properties in vitro, to elucidate the mechanism of its antioxidative effects, the reaction products of sesamin in rat liver homogenate were analyzed. The methylenedioxyphenyl moiety in the structure of sesamin was shown to be changed into a dihydrophenyl (catechol) moiety. The enzymatic reaction products in vitro were identified as (1R,2S,5R,6S)-6-(3,4-dihydroxyphenyl)-2-(3,4-methylenedioxyphenyl)-3,7-dioxabicyclo[3,3,0]octane and (1R,2S,5R,6S)-2,6-bis(3,4-dihydroxyphenyl)-3,7-dioxabicyclo[3,3,0]octane, which showed strong radical scavenging activities; the latter was a novel compound. The same metabolites were found as glucuronic acid and/or sulfic acid conjugates in substantial amounts in rat bile after oral administration of sesamin. It is suggested that sesamin is a prodrug and the metabolites containing the catechol moieties in their structures are responsible for the protective effects of sesamin against oxidative damage in the liver.