The AKR1C family of aldo-keto reductase (AKR) includes AKR1C1 (20-alpha-hydroxysteroid dehydrogenase, also known as 20alpha-HSD), AKR1C2 (3alpha-HSD type 3), AKR1C3 (17beta-HSD type 5), and AKR1C4 (3alpha-HSD type 1) from Homo sapiens; AKR1C5 (20alpha-HSD, also known as prostaglandin-E(2) 9-reductase) from Rattus norvegicus (ovary); AKR1C6 (estradiol 17beta-HSD type 5) from Mus musculus; AKR1C7 (prostaglandin F synthase 1 or PGF1) from Bos taurus (lung); AKR1C8 (20alpha-HSD) from Rattus norvegicus (ovary); AKR1C9 (3alpha-HSD) from Rattus norvegicus (liver); AKR1C10a (Rho crystallin) from Rana temporaria and AKR1C10b (Rho crystallin) from Rana catesbeina; AKR1C11 (prostaglandin F synthase 2 or PGF2) from Bos taurus (liver); AKR1C12 (aldo-keto reductase or AKR), AKR1C13 (interleukin-3-regulated AKR), and AKR1C14 (3alpha-HSD) from Mus musculus; AKR1C15 (NADPH-dependent reductase), AKR1C16 (NAD+-preferring 3alpha/17beta/20alpha-HSD), and AKR1C17 (NAD+-dependent 3alpha-HSD) from Rattus norvegicus; AKR1C18 (20alpha-HSD), AKR1C19 (3-hydroxybutyrate dehydrogenase or 3HB dehydrogenase), AKR1C20 (3alpha(17beta)-HSD), AKR1C21 (3(17)alpha-HSD), AKR1C22 (dihydrodiol dehydrogenase or DD) from Mus musculus; AKR1C23 (20alpha-HSD) from Equus caballus; AKR1C24 (NAD+-dependent 17beta-HSD) from Rattus norvegicus; AKR1C25 (3(20)alpha-HSD) from Macaca fuscata; AKR1C26 (identical to morphine 6-dehydrogenase or M6DH, acts as NAD(+)-dependent 3alpha/17beta-HSD), AKR1C27/AKR1C28 (NAD(+)-dependent 3alpha/17beta-HSDs), AKR1C29 (identical to 3-hydroxyhexobarbital dehydrogenase or 3HBD, acts as NADPH-preferring reductase with 3alpha/3beta/17beta/20alpha-HSD activity), AKR1C30 (identical to naloxone reductase type 1 and acts as 17beta-HSD), AKR1C31 (3alpha/17beta/20alpha-HSD), AKR1C32 (identical to loxoprofen reductase and acts as 3alpha/20alpha-HSD), and AKR1C33 (identical to naloxone reductase type 2 and mainly acts as 3alpha-HSD) from Oryctolagus cuniculus; AKR1C34 (NAD+-dependent morphine 6-dehydrogenase or M6DH with 3beta/17beta/20alpha-HSD activity) and AKR1C35 (NAD+-dependent dehydrogenase with 3(17)beta-HSD activity) from Mesocricetus auratus.