PDF(Pubmed)
Abstract：
NADPH, the primary source of reducing equivalents in the cytosol, is used in vertebrate rod photoreceptor outer segments to reduce the all-trans retinal released from photoactivated visual pigment to all-trans retinol. Light activation of the visual pigment isomerizes the 11-cis retinal chromophore to all-trans, thereby destroying it and necessitating its regeneration. Release and reduction of all-trans retinal are the first steps in the series of reactions that regenerate the visual pigment. Glucose and glutamine can both support the reduction of all-trans retinal to retinol, indicating that the NADPH used in rod photoreceptor outer segments can be generated by the pentose phosphate pathway as well as by mitochondria-linked pathways. We have used the conversion of all-trans retinal to all-trans retinol to examine whether amino acids other than glutamine can also support the generation of NADPH in rod photoreceptors. We have measured this conversion in single isolated mouse rod photoreceptors by imaging the fluorescence of the all-trans retinal and retinol generated after exposure of the cells to light. In agreement with previous work, we find that 5 mM glucose or 0.5 mM glutamine support the conversion of ∼70-80% of all-trans retinal to retinol, corresponding to a reduced NADP fraction of ∼10%. All other amino acids at 0.5 mM concentration support the conversion to a much lesser extent, indicating reduced NADP fractions of 1-2% at most. Taurine was also ineffective at supporting NADPH generation, while formic acid, the toxic metabolite of methanol, suppressed the generation of NADPH by either glucose or glutamine.
摘要：
NADPH,胞质溶胶中还原当量的主要来源，用于脊椎动物杆状感光体外段，以减少从光激活的视觉色素释放的全反式视网膜到全反式视黄醇。视觉色素的光活化将11-顺式视网膜发色团异构化为全反式，从而摧毁它并需要它的再生。全反式视黄醛的释放和减少是再生视觉色素的一系列反应中的第一步。葡萄糖和谷氨酰胺都可以支持全反式视黄醛减少到视黄醇，表明杆状光感受器外节段中使用的NADPH可以通过戊糖磷酸途径以及线粒体连接的途径产生。我们已经使用全反式视黄醛到全反式视黄醇的转化来检查除谷氨酰胺以外的氨基酸是否也可以支持杆状光感受器中NADPH的产生。我们已经通过对细胞暴露于光后产生的全反式视黄醛和视黄醇的荧光进行成像，在单个分离的小鼠杆状光感受器中测量了这种转化。与以前的工作一致，我们发现5mM葡萄糖或0.5mM谷氨酰胺支持70-80%的全反式视黄醛向视黄醇的转化，对应于10%的NADP分数降低。0.5mM浓度的所有其他氨基酸支持转化的程度要小得多，表明NADP分数最多减少1-2%。牛磺酸在支持NADPH生成方面也无效，而甲酸，甲醇的有毒代谢产物,通过葡萄糖或谷氨酰胺抑制NADPH的产生。
