Substrate specificity and subcellular localization of the aldehyde-alcohol redox-coupling reaction in carp cones.
Our previous study suggested the presence of a novel cone-specific redox reaction that generates 11-cis-retinal from 11-cis-retinol in the carp retina. This reaction is unique in that 1) both 11-cis-retinol and all-trans-retinal were required to produce 11-cis-retinal; 2) together with 11-cis-retinal, all-trans-retinol was produced at a 1:1 ratio; and 3) the addition of enzyme cofactors such as NADP(H) was not necessary. This reaction is probably part of the reactions in a cone-specific retinoid cycle required for cone visual pigment regeneration with the use of 11-cis-retinol supplied from Müller cells. In this study, using purified carp cone membrane preparations, we first confirmed that the reaction is a redox-coupling reaction between retinals and retinols. We further examined the substrate specificity, reaction mechanism, and subcellular localization of this reaction. Oxidation was specific for 11-cis-retinol and 9-cis-retinol. In contrast, reduction showed low specificity: many aldehydes, including all-trans-, 9-cis-, 11-cis-, and 13-cis-retinals and even benzaldehyde, supported the reaction. On the basis of kinetic studies of this reaction (aldehyde-alcohol redox-coupling reaction), we found that formation of a ternary complex of a retinol, an aldehyde, and a postulated enzyme seemed to be necessary, which suggested the presence of both the retinol- and aldehyde-binding sites in this enzyme. A subcellular fractionation study showed that the activity is present almost exclusively in the cone inner segment. These results suggest the presence of an effective production mechanism of 11-cis-retinal in the cone inner segment to regenerate visual pigment.
From the Department of Biological Sciences, Graduate School of Science, and.
Shinya
S
Sato
Takashi
T
Fukagawa
Shuji
S
Tachibanaki
Yumiko
Y
Yamano
Akimori
A
Wada
Satoru
S
Kawamura
D000438:Alcohols / Q000378:metabolism; D000818:Animals; D001547:Benzaldehydes / Q000378:metabolism; D001665:Binding Sites; D002347:Carps; D007425:Intracellular Membranes / Q000378:metabolism*; D010084:Oxidation-Reduction; D017949:Retinal Cone Photoreceptor Cells / Q000378:metabolism*; D055211:Retinal Photoreceptor Cell Inner Segment / Q000378:metabolism; D012172:Retinaldehyde / Q000378:metabolism*; D013379:Substrate Specificity; D014801:Vitamin A / Q000031:analogs & derivatives / Q000378:metabolism*
D000438:Alcohols; D001547:Benzaldehydes; D014801:Vitamin A; D012172:Retinaldehyde; C032175:benzaldehyde
Cones; Müller Cells; Photoreceptors; Retinal Metabolism; Retinoid; Retinoid Cycle; Vision; Vitamin A