The regulation of the rat epididymal steroid metabolizing enzymes, (DELTA)('4)-5(alpha)-reductase and 3(alpha)-hydroxysteroid dehydrogenase (3(alpha)-HSD), was investigated during sexual maturation. Nuclear (DELTA)('4)-5(alpha)-reductase activity was first detected at day 21 and reached maximal values by day 77. Subsequently, enzymatic activity declined by more than 60% to reach adult plateau levels by day 105. Cytoplasmic 3(alpha)-HSD was already evident in the youngest age group tested (day 7) and reached the characteristic adult plateau levels by day 63. While 3(alpha)-HSD activity correlated closely with androgen-dependent parameters during development, nuclear (DELTA)('4)-5(alpha)-reductase activity correlated neither with the presence of spermatozoa nor with parameters of androgen levels. To investigate the subcellular distribution of (DELTA)('4)-5(alpha)-reductase and 3(alpha)-HSD during development, a discontinuous sucrose gradient method was developed. While 3(alpha)-HSD activity was found solely in cytoplasmic fractions, (DELTA)('4)-5(alpha)-reductase activity was present only in nuclear and microsomal fractions. In contrast to the bell-shaped developmental profile of nuclear (DELTA)('4)-5(alpha)-reductase activity, the activity of microsomal (DELTA)('4)-5(alpha)-reductase increased gradually with age. / To adequately compare the biochemical properties of nuclear and microsomal (DELTA)('4)-5(alpha)-reductase, enzymatic activity was solubilized. The sedimentation coefficient of solubilized (DELTA)('4)-5(alpha)-reductase was greater for the microsomal enzyme than for the nuclear enzyme (11.6S(' )vs(' )10.1S). The relative capacity of steroids to inhibit enzymatic activity and the pH optima were similar for nuclear and microsomal, membrane-bound and solubilized enzyme forms. While the Km for testosterone was similar in nuclear and microsomal fractions (range: 1.75-4.42 x 10('-7)M), the Km for NADPH was about 30-fold greater for the microsomal enzyme than for the nuclear enzyme. / Thus, (1) 3(alpha)-HSD activity is androgen-dependent and found only in the cytoplasmic fraction; (2) (DELTA)('4)-5(alpha)-reductase activity is regulated by a factor(s) not relating directly to either spermatozoa or androgens; (3) (DELTA)('4)-5(alpha)-reductase activity is regulated as a function of age and subcellular distribution; (4) (DELTA)('4)-5(alpha)-reductase activity can be solubilized in an active and stable form with no major alterations in the active site of the enzyme; (5) there apparently exists at least two distinct forms of (DELTA)('4)-5(alpha)-reductase in the epididymis.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.68668 |
| Date | January 1982 |
| Creators | Scheer, Heimo W. |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Doctor of Philosophy (Department of Pharmacology and Therapeutics) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 000157036, proquestno: AAINK60994, Theses scanned by UMI/ProQuest. |
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