All-trans-retinol 13,14-reductase (RETSAT) is an ER membrane-associated protein that mediates the saturation of the 13-14 double bond of all-trans-retinol (atROL) to produce all-trans-13,14-dihydroretinol (at-13,14-dhROL). The product formed is a metabolite of unknown biological function. The human activity of RETSAT is inferred from mouse Retsat enzyme assays (Moise et al. 2004). In human and mouse, RETSAT is induced during adipogenesis and is directly regulated by the transcription factor peroxisome proliferator activated receptor gamma (PPAR-gamma). Ablation of RETSAT inhibits adipogenesis but this block was not overcome by the product of RETSAT enzymatic activity. In adipose tissue, RETSAT is expressed in adipocytes but is downregulated in obesity. RETSAT could be a novel target for therapeutic intervention in metabolic disease (Schupp et al. 2009).