Fig. 3.

Simplified version of the retinoid pathway. Retinol (combined with retinol-binding protein-RBP) passes through the cellular membrane using the stimulated by retinoic acid 6 receptor (STRA6), is carried by the cellular retinol-binding protein (CRBPs), and transformed into retinaldehyde (Ral) by alcohol dehydrogenase (ADH) or retinol dehydrogenase (RDH). β-Carotene after its entry into the cells is directly transformed into Ral, which is then transformed into retinoic acids (RAs) by retinaldehyde dehydrogenase. RAs are then bound to cellular retinoic acid-binding protein (CRABPs) and enter the nucleus