Cellular retinol binding protein action

Preformed vitamin A, most often in the form of retinyi ester, or carotenoids are subject to emulsification and mised micelle formation by the action of bile salts before being transported into the intestinal cell. Here the retinyi esters are moved across the mucosal membrane and hydrolyzed to retinol within the cell to then be reesterified by cellular retinol-binding protein II and packaged into chylomicra, which then enter the mesenteric lymphatic system and pass mto the systemic circulation. A small amount of the ingested retinoid is also converted into retinoic acid in the intestinal cell. The efficiency of absorption of preformed vitamin A is high at between 70% and 90%. ... 

From the effects of its deficiency it appears that vitamin A is required for the controlled division and differentiation of cells. Retinol is delivered to specific sites on the cell surface that recognize the RBP and cause it to release the retinol. Once inside the cell the retinol combines with the cellular retinol-binding protein and retinoic acid with cellular retinoic acid-binding protein and each is delivered to nuclear binding sites which may be important in gene expression. Thus their mode of action resembles that of the steroid hormones (page 349). 

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