ESTERIFICATION OF RETINOL

LRAT: Lecithin:retinol-acyltransferase esterifies retinol at physiological concentrations of retinol. LRAT uses retinol bound to CRBPII and a fatty acid from phosphatidylcholine.

ARAT: Acyl-CoA-retinol acyltransferase esterifies retinol at high concentrations of retinol. Esterifies unbound/free retinol.

mRNA-levels of LRAT in vitamin A deficient and normal rodents

Reza Zolfaghari and A. Catharine Ross: Lecithin:retinol acyltransferase from mouse and rat liver: cDNA cloning and liver-specific regulation by dietary vitamin A and retinoic acid. Journal of Lipid Research Volume 41, 2000

This article shows how RA upregulates LRAT expression. The lower figure shows an ethidium bromide-coloured agarose gel of LRAT mRNA amplified by RT-PCR. We see that in rats with sufficient vitamin A in the diet LRAT is expressed. In vitamin A poor rats LRAT level is much lower. In rats who have had a dose or two of retinoic acid, LRAT is upregulated. The top picture shows quantification of the bands on the gel. These results support the hypothesis (below) that retinoic acid stimulates esterification of retinol for storage by inducing expression of LRAT.

Figure (A)RT-PCR analysis of total RNA, in the liver of vitamin A-deficient, retinoic acid (RA)-treated and vitamin A-sufficient rats. (B) Ethidium bromide-stained agarose gel of the LRAT RT-PCR products amplified from rat liver total RNA, as quantified in (A).

Retinoic acid stimulates esterification of retinol for storage by inducing expression of LRAT

Reza Zolfaghari and A. Catharine Ross: Lecithin:retinol acyltransferase from mouse and rat liver: cDNA cloning and liver-specific regulation by dietary vitamin A and retinoic acid. Journal of Lipid Research Volume 41, 2000

Figure Retinoic acid switches on LRAT-expression, thereby stimulating retinol esterification and storage.
A negative feedback mechanism.