Figure 5.

Vitamin A (retinol) as the starting compound for biosynthesis of retinoic acid (RA) in the cells.

In the cytoplasm, retinol remains bound to cellular retinol-binding proteins (CRBPs) for its movement and role in metabolism, but RA remains bound to cellular RA-binding proteins (CRABPs) for its movement for regulating many signaling pathways. Also, RA with the help of CRABPs can move to the nuclear receptors (RARs and RXRs) for expression of specific genes. RARs: Retinoic acid receptors; RXRs: retinoid X receptors.