Lecithin:Retinol Acyltransferase Is Responsible for Amidation of Retinylamine, a Potent Inhibitor of the Retinoid Cycle

Marcin Golczak,Yoshikazu Imanishi,Vladimir Kuksa,Tadao Maeda,Ryo Kubota,Krzysztof Palczewski

doi:10.1074/jbc.m509351200

Marcin Golczak, Yoshikazu Imanishi + Show 4 more

Open Access

https://doi.org/10.1074/jbc.m509351200

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Abstract

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.

Highlights

The key step in the transformation of all-trans-retinal to 11-cis-retinal is the isomerization reaction
We have suggested that the regeneration of the chromophore might occur through a retinyl carbocation intermediate [12] and demonstrated that isomerization is inhibited by positively charged retinoids [13]
In Stargardt disease, a disease associated with mutations in the photoreceptor-specific ATP-binding cassette transporter (ABCR) [14] or elongation of the very long chain fatty acidlike 4 protein (ELOVL 4) [15, 16], the accumulation of all-trans-retinal is thought to be responsible for the formation of a component of a lipofuscin pigment called A2E

Summary

Introduction

The key step in the transformation of all-trans-retinal to 11-cis-retinal is the isomerization reaction. In the case of the liver extract, 10 and 100 ␮l of retinoid solution were injected on an HPLC column for the detection of N-retinylamides and Ret-NH2, respectively. To determine the radioactivity distribution among retinoids found in the liver of animals gavaged with 11,12-[3H]alltrans-Ret-NH2 or 11,12-[3H]N-all-trans-retinylamide, products corresponding to the retinyl esters, retinol, retinylamides, and RetNH2 were collected during an HPLC run.

Results

Conclusion