ABSTRACT
Microsomal retinoic acid synthesis is quantitatively minor (51) and doesn't appear sufficient to consume the retinal generated. Cytosol has much more active retinal dehydrogenase activity. To determine whether retinal produced from holo-CRBP by microsomes could generate retinoic acid in cytosol, rat liver cytosol was partitioned into two fractions by anion-exchange chromatography: Pl (not retained) and P2 (retained). Both Pl and P2 recognized free retinal as substrate, with NAD as cofactor (data not shown), but only Pl synthesized substantial amounts of retinoic acid from the retinal generated in situ from holo-CRBP, liver microsomes, and NADP (Figure 10). Pl (25 1-1g protein) supported relatively high rates of retinoic acid synthesis, but P2 (up to 800 1-1g protein) provided low amounts of retinoic acid ( -4 pmol).
