ABSTRACT
This chapter reviews many mammalian 17–hydroxysteroid dehydrogenases that are components of the membrane structure of cellular organelles. The 17–hydroxysteroid dehydrogenases 17–oxidoreductases are pyridine nucleotide–dependent enzymes that catalyze the stereospecific interconversion of the hydroxyl and carbonyl groups at C–17 of the C18 and C19 steroids. Studies on the subcellular distribution of the 17–hydroxysteroid dehydrogenases of mammalian systems have shown that the enzymes are located in the particulate fractions of some tissues and are soluble enzymes in other tissues. Some tissues have both soluble and particulate activities. Such is the case in rabbit liver, where 17β–hydroxysteroid dehydrogenase activity toward androgens and estrogens is present in both the microsomal and soluble fractions. Although the 17-hydroxysteroid dehydrogenases have many properties in common, there are differences in subcellular distribution, substrate specificity, and pyridine nucleotide specificity among the enzymes of different tissues which probably reflect the specific functions of the enzymes in various tissues.
