Masaaki Katsuyama

Reductive metabolic pathways of carotenoids in fish (3S, 3'S)-astaxanthin to tunaxanthin A, B, and C

Abstract 1. 1. A stereochemical approach based on the isolated and composed carotenoids in marine fish-eggs being different from those in mature fish led to the elucidation of the following reductive metabolic pathways of (3S,3′S)-astaxanthin. These pathways can be divided into two groups: (i) those that metabolize (3S,3′S)-astaxanthin into (3R,3′R)-zeaxanthin via (3S,4RS,3′R)-β,β-carotene-3,4,3′-triol (i.e. mackerel and yellowtail); (ii) those that metabolize (3S,3′S)-astaxanthin into tunaxanthin A, B and C [(3S,6S,3′S,6′S)-, (3R,6S,3′S,6′S)- and (3R,6S,3′R,6′S)-ϵ,ϵ-carotene-3,3′-diol, respectively] via (3R,3′R)-zeaxanthin, (3R,6′S)-3-hydroxy-β,ϵ-caroten-3′-one and (6S,6′S)-ϵ,ϵ-carotene-3,3′-dione (i.e. dolphin and flying fish). 2. 2. These carotenoids, (3R,6′S)-3-hydroxy-β,ϵ-caroten-3′-one and (6S,6′S)-ϵ,ϵ-carotene-3,3′-dione are the first examples as precursors of tunaxanthin A, B and C in fish. 3. 3. Both (3R,3′S,6′S)-β,ϵ-carotene-3,3′-diol and (3R,3′R,6′S)-β,ϵ-carotene-3,3′-diol, which are stereoisomers of lutein, were isolated from the eggs of dolphin and flying fish. The former is the first report in naturally occurring carotenoid and the latter is new. 4. 4. The carotenoid compositions were varied according to the degree of maturation in four kinds of marine fish-eggs. Namely, the occurrence of (3R,3′R)-zeaxanthin and tunaxanthin A, B and C increased, while (3S,3′S)-astaxanthin decreased proportionally with increasing maturation stage.

METABOLISM OF CAROTENOIDS IN THE APPLE SNAIL, POMACEA CANALICULATA

Abstract Feeding experiments with β , β -carotene, canthaxanthin, (3 R ,3′ R )-zeaxanthin, (3 R ,3′ R ,6′ R )-lutein and racemic astaxanthin on the apple snail Pomacea canaliculata were investigated. Based on the experimental results, β , β -carotene was oxidatively metabolized, and the resulting principal metabolic product (3 S ,3′ S )-astaxanthin along with other keto carotenoids such as (3 S )-3-hydroxy- β -echinenone, canthaxanthin, (3 S ,3′ R )-4-ketozeaxanthin and (3 S )-phoenicoxanthin was accumulated in the gonad. Similarly, (3 R ,3′ R ,6′ R )-lutein was converted into fritschiellaxanthin [(3 S ,3′ R ,6′ R )-3,3′-dihydroxy- β , ϵ-caroten-4-one]. It was concluded that P. canaliculata had the ability to oxidize the C-3, 4 positions on the β -end group.