Substrate Specificity and Subcellular Localization of the Aldehyde-Alcohol Redox-coupling Reaction in Carp Cones

作者：Sato Shinya; Fukagawa Takashi; Tachibanaki Shuji; Yamano Yumiko; Wada Akimori; Kawamura Satoru^*

来源：Journal of Biological Chemistry, 2013, 288(51): 36589-36597.

DOI：10.1074/jbc.M113.521153

• Photoreceptors
• Retinal Metabolism
• Retinoid
• Vision
• Vitamin A
• Cones
• Muller Cells
• Retinoid Cycle

Background: In carp cones, 11-cis-retinal and all-trans-retinol are formed with 11-cis-retinol and all-trans-retinal present. Results: The substrate specificity, reaction mechanism, and subcellular localization of this reaction were determined. Conclusion: Substrate specificity is high for retinol but low for retinal, and the activity is present in the cone inner segment. Significance: The possible contribution to efficient pigment regeneration in cones is suggested.
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 Muller 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.

• 出版日期2013-12-20