The metabolic pathway of visual pigment chromophore formation in Drosophila melanogaster--all-trans (3S)-3-hydroxyretinal is formed from all-trans retinal via (3R)-3-hydroxyretinal in the dark.
Carotenoid-depleted fruit flies, Drosophila melanogaster, were reared on yeast/glucose medium containing lipid-depleted white corn grits and cholesterol. After rearing for more than a year, the yield of flies remained constant and the content of 3-hydroxyretinal in a head was three logarithmic units less than that of normal flies reared on medium containing yellow corn grits. When all-trans retinal was supplied as the sole source of retinoids, the flies formed and accumulated all-trans 3-hydroxyretinal in the dark. To examine the metabolic pathway to produce (3S)-3-hydroxyretinal in Drosophila, all-trans retinal was supplemented for two hours to carotenoid-depleted flies in the dark, and the subsequent changes in the composition of 3-hydroxyretinal enantiomers were analyzed using a chiral column on HPLC. The results indicated initial formation of (3R)-3-hydroxyretinal followed by isomerization into the 3S enantiomer. In another set of experiments, the membrane fraction was obtained from the head homogenate of retinoid-depleted flies and an in vitro assay of 3-hydroxyretinal formation from retinal was performed. The 3-hydroxyretinal produced was the 3R enantiomer, supporting the result obtained from the in vivo experiment whereby (3S)-3-hydroxyretinal is produced from retinal via (3R)-3-hydroxyretinal. Addition of NADPH enhanced 3-hydroxyretinal formation and the presence of carbon monoxide inhibited it, suggesting that hydroxylation at the C3 position of retinal occurred via the monooxygenase activity of cytochrome P-450.
Seki
T
T
Division of Health Science, Osaka Kyoiku University, Kashiwara, Japan. seki@cc.osaka-kyoiku.ac.jp
Isono
K
K
Ozaki
K
K
Tsukahara
Y
Y
Shibata-Katsuta
Y
Y
Ito
M
M
Irie
T
T
Katagiri
M
M
D000818:Animals; D003624:Darkness; D004331:Drosophila melanogaster / Q000378:metabolism*; D012168:Retinal Pigments / Q000096:biosynthesis*; D012172:Retinaldehyde / Q000008:administration & dosage / Q000031:analogs & derivatives / Q000096:biosynthesis* / Q000378:metabolism
D012168:Retinal Pigments; D012172:Retinaldehyde