title: C19 steroidal precursors of estrogens.
abstract: The pathways of biosynthesis of the estrogens from C19 steroids has been examined by in vitro kinetic experiments using human placental microsomes and two precursors, each labeled with a different radioisotope. The results indicate that under the conditions employed, androstenedione is an obligatory intermediate in the conversion of 3 beta-hydroxy-5-androsten-17-one (dehydroisoandrosterone) or its sulfate, dehydroisoandrosterone sulfate, into estrone and estradiol. The same result was obtained when the microsomal fraction was replaced by either a 1000 x g supernatant preparation from human placenta or a homogenate of placental mitochondria. If alternative pathways involving C19-hydroxylated derivatives of dehydroisoandrosterone or its sulfate exist, they appear to be of minor quantitative significance.
mesh_terms: D000735:Androstenedione / Q000378:metabolism; D002250:Carbon Radioisotopes; D003687:Dehydroepiandrosterone / Q000378:metabolism*; D004967:Estrogens / Q000096:biosynthesis*; D005260:Female; D006801:Humans; D007553:Isotope Labeling; D007700:Kinetics; D008861:Microsomes / Q000378:metabolism*; D010920:Placenta / Q000378:metabolism*; D011247:Pregnancy; D014316:Tritium
chemical_list: D002250:Carbon Radioisotopes; D004967:Estrogens; D014316:Tritium; D000735:Androstenedione; D003687:Dehydroepiandrosterone