Stage-related changes in steroid-converting enzyme activities in Squalus testis: synthesis of biologically active metabolites via 3 beta-hydroxysteroid dehydrogenase/isomerase and 5 alpha-reductase.
To investigate the relationship between steroidogenesis and spermatogenesis, two key enzymes of androgen biosynthesis, 3 beta-hydroxysteroid dehydrogenase/isomerase (3 beta-HSD) and 5 alpha-reductase, were compared at premeiotic (PrM), meiotic (M), and postmeiotic (PoM) stages. Staged tissues were obtained by dissection from the testis of the spiny dogfish Squalus acanthias, in which spermatogenesis is a simple diametric progression. Microsomal 3 beta-HSD activity was measured by conversion of [3H]dehydroepiandrosterone (DHEA) to androstenedione (AE). Reaction constants were: Km = 3.2 microM and Vmax = 243 pmol/min/mg protein. 3 beta-HSD increased progressively with maturation, resulting in three- to four-fold higher levels in PoM than in PrM stages. Absolute values and stage-related differences were the same, whether microsomes were derived from whole testis or from isolated spermatocysts (germ cell/Sertoli cell units), thus supporting microscopic studies showing that Sertoli cells are the primary steroidogenic elements of dogfish testis. In vitro conversion of [3H]testosterone to [3H]dihydrotestosterone (DHT) was used to estimate 5 alpha-reductase activity. Apparent substrate affinity was similar to that of 3 beta-HSD (Km = 2.9 microM), but maximal product yields were two to three orders of magnitude lower (Vmax = 208 fmol/min/mg protein). Also, the stage-related pattern of 5 alpha-reductase activity (PrM > PoM >> M) differed from that of 3 beta-HSD (PoM >> M > PrM).(ABSTRACT TRUNCATED AT 250 WORDS)
Cuevas
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ME
Department of Biology, Boston University, MA 02215.
Collins
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Callard
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GV
D013741:3-Oxo-5-alpha-Steroid 4-Dehydrogenase / Q000378:metabolism*; D000735:Androstenedione / Q000378:metabolism; D000818:Animals; D003687:Dehydroepiandrosterone / Q000378:metabolism; D013196:Dihydrotestosterone / Q000378:metabolism; D008297:Male; D008540:Meiosis; D008861:Microsomes / Q000201:enzymology; D009097:Multienzyme Complexes / Q000378:metabolism*; D011375:Progesterone Reductase / Q000378:metabolism*; D012621:Seasons; D012754:Sharks / Q000378:metabolism*; D013091:Spermatogenesis; D013251:Steroid Isomerases / Q000378:metabolism*; D013737:Testis / Q000201:enzymology* / Q000254:growth & development; D013739:Testosterone / Q000378:metabolism
C021425:3 beta-hydroxysteroid oxidoreductase-delta(5) 3-ketosteroid isomerase; D009097:Multienzyme Complexes; D013196:Dihydrotestosterone; D013739:Testosterone; D000735:Androstenedione; D003687:Dehydroepiandrosterone; D011375:Progesterone Reductase; D013741:3-Oxo-5-alpha-Steroid 4-Dehydrogenase; D013251:Steroid Isomerases