Versatile enzyme presenting two types of activity; L-3-hydroxyacyl-CoA dehydrogenase ((3S)-3-hydroxyacyl-CoA dehydrogenase) activity and hydroxysteroid dehydrogenase (HSD) activity with a wide substrate spectrum. As a (3S)-3-hydroxyacyl-CoA dehydrogenase, it functions in the third step of the fatty acid beta-oxidation pathway, a major metabolic process in which fatty acids are oxidized to provide a significant source of energy, while also generating acyl-CoA metabolites used by many metabolic routes (PubMed:12917011) (Probable). As a HSD, it functions in the degradation pathways of glucocorticoids and sex steroids and epimerization of bile acids; catalyzes the beta-oxidation at position 17 of androgens and estrogens, has 3-alpha-hydroxysteroid dehydrogenase activity with androsterone, and carries out oxidative conversions of 7-beta-hydroxylated bile acids like ursodeoxycholate or isoursodeoxycholate (also known as 3-beta,7-beta-dihydroxy-5-beta-cholan-24-oate or 7-beta-hydroxyisolithocholate, respectively). Also exhibits 20-beta-OH and 21-OH dehydrogenase activities with C21 steroids (PubMed:12917011). Required for cell survival during embryonic development. May play a role in germline formation (PubMed:9585418, PubMed:12917011). a (3S)-3-hydroxyacyl-CoA + NAD(+) = a 3-oxoacyl-CoA + H(+) + NADH (3S)-3-hydroxybutanoyl-CoA + NAD(+) = acetoacetyl-CoA + H(+) + NADH NAD(+) + testosterone = androst-4-ene-3,17-dione + H(+) + NADH 5alpha-androstane-3alpha,17beta-diol + NAD(+) = 17beta-hydroxy-5alpha-androstan-3-one + H(+) + NADH 17beta-estradiol + NAD(+) = estrone + H(+) + NADH NAD(+) + ursodeoxycholate = 7-oxolithocholate + H(+) + NADH 3beta,7beta-dihydroxy-5beta-cholan-24-oate + NAD(+) = 3beta-hydroxy-7-oxo-5beta-cholan-24-oate + H(+) + NADH 11-dehydrocorticosterone + NAD(+) = H(+) + NADH + pregn-4-ene-3,11,20,21-tetraone cortisone + NAD(+) = 17alpha-hydroxypregn-4-en-3,11,20-trione-21-al + H(+) + NADH cortisol + NAD(+) = 11beta,17alpha-dihydroxypregn-4-ene-3,20,21-trione + H(+) + NADH 5alpha-pregnan-20beta-ol-3-one + NAD(+) = 5alpha-pregnane-3,20-dione + H(+) + NADH 17beta-hydroxy-5alpha-androstan-3-one + NAD(+) = 5alpha-androstan-3,17-dione + H(+) + NADH Optimum pH is 9.3 for the dehydrogenase reaction, and 6.4 for the reductase reaction. Multimer. Localizes to the lipid droplet fraction in early embryos (PubMed:16979555). Co-localization with mitochondrial markers for human, but not for the Drosophila form (PubMed:12917011). Found in many tissues including CNS, imaginal disks and salivary glands. Highest expression in both embryonic gonadal primordia and mature ovaries and testes. Expressed throughout embryonic development. In adults, expression is higher in females than in males. By 20-hydroxyecdysone. Embryonic and pupal lethal. Male mutants show small testes and degenerating spermatocytes with a large accumulation of small fat-containing vesicles in the cytoplasm and almost no mitochondria. Null mutant photoreceptors fail to differentiate normally, are unable to form proper rhabdomeres and present smaller mitochondria with fewer, but swollen crestae, than wild-type cells. Belongs to the short-chain dehydrogenases/reductases (SDR) family. Extended N-terminus.