Golczak Marcin, Imanishi Yoshikazu, Kuksa Vladimir, Maeda Tadao, Kubota Ryo, Palczewski Krzysztof
Department of Ophthalmology, University of Washington and Acucela Inc., Seattle, Washington 98195, USA.
J Biol Chem. 2005 Dec 23;280(51):42263-73. doi: 10.1074/jbc.M509351200. Epub 2005 Oct 10.
Lecithin:retinol acyltransferase (LRAT) catalyzes the transfer of an acyl group from the sn-1 position of phosphatidylcholine to all-trans-retinol (vitamin A) and plays an essential role in the regeneration of visual chromophore as well as in the metabolism of vitamin A. Here we demonstrate that retinylamine (Ret-NH2), a potent and selective inhibitor of 11-cis-retinal biosynthesis (Golczak, M., Kuksa, V., Maeda, T., Moise, A. R., and Palczewski, K. (2005) Proc. Natl. Acad. Sci. U. S. A. 102, 8162-8167), is a substrate for LRAT. LRAT catalyzes the transfer of the acyl group onto Ret-NH2 leading to the formation of N-retinylpalmitamide, N-retinylstearamide, and N-retinylmyristamide with a ratio of 15:6:2, respectively. The presence of N-retinylamides was detected in vivo in mice supplemented with Ret-NH2. N-Retinylamides are thus the main metabolites of Ret-NH2 in the liver and the eye and can be mobilized by hydrolysis/deamidation back to Ret-NH2. Using two-photon microscopy and the intrinsic fluorescence of N-retinylamides, we showed that newly formed amides colocalize with the retinyl ester storage particles (retinosomes) in the retinal pigment epithelium. These observations provide new information concerning the substrate specificity of LRAT and explain the prolonged effect of Ret-NH2 on the rate of 11-cis-retinal recovery in vivo.
视黄醇酰基转移酶（LRAT）催化酰基从磷脂酰胆碱的sn-1位转移至全反式视黄醇（维生素A），在视觉发色团的再生以及维生素A的代谢中发挥着重要作用。在此我们证明，视黄胺（Ret-NH2），一种11-顺式视黄醛生物合成的强效选择性抑制剂（戈尔恰克，M.，库克萨，V.，前田，T.，莫伊斯，A. R.，以及帕尔采夫斯基，K.（2005年）《美国国家科学院院刊》102卷，8162 - 8167页），是LRAT的一种底物。LRAT催化将酰基转移到Ret-NH2上，分别以15:6:2的比例生成N-视黄基棕榈酰胺、N-视黄基硬脂酰胺和N-视黄基肉豆蔻酰胺。在补充了Ret-NH2的小鼠体内检测到了N-视黄基酰胺的存在。因此，N-视黄基酰胺是Ret-NH2在肝脏和眼睛中的主要代谢产物，并且可以通过水解/脱酰胺作用被动员回Ret-NH2。利用双光子显微镜和N-视黄基酰胺的固有荧光，我们表明新形成的酰胺与视网膜色素上皮中的视黄酯储存颗粒（视网膜小体）共定位。这些观察结果提供了关于LRAT底物特异性的新信息，并解释了Ret-NH2对体内11-顺式视黄醛恢复速率的延长作用。
