Figure 20.

Structure and catalytic mechanism of RDHs. (a) Cartoon representation of a representative SDR family member (type 1 17-β-hydroxysteroid dehydrogenase, PDB accession code 1A27). (b) Hypothetical structure of an RDH with bound nucleotide (NAD(H) or NADP(H)) and retinoid (all-trans-retinol or all-trans-retinal) substrate. The structures in panels a and b are depicted in the same orientation. (c) Reversible transfer of hydride from the S4-face of the nucleotide to all-trans-retinal to produce pro-R-all-trans-retinol.