Subcellular location for the formation of the retinol/retinol-binding protein complex in rat liver

Retinol complexes with retinol-binding protein (RBP) within the hepatocyte, however the subcellular location where complex formation occurs has not previously been identified. A model similar to that of lipoproteins formation has been hypothesized. The authors have identified the initial site of retinol/RBP complex formation. Furthermore, the authors have elucidated the progression of the complex through the subcellular organelles. Intravenous injections of 3H-retinol suspended in Tween 40 were administered to vitamin A depleted rats. After intervals of 2, 3, 4, 5, 10, 15, 20, and 30 minutes the rat livers were removed and fractions enriched in rough and smooth microsomes and Golgi apparatus were prepared. Extracts of these subcellular fractions were chromatographed on Sephadex G-100. Simultaneous elution of 3H-retinol and immunoreactive RBP indicated the presence of the complex. The retinol/RBP complex was observed in rough microsomes 2 minute after the injection of 3H-retinal. The complex appeared subsequently in smooth microsomes and Golgi apparatus. The complex was first detected serum around 10 minutes after injection. Based on the data, they believe that the retinol/RBP complex formation occurs in rough microsomes