Ronald C. Strickler

Human placental 3β-hydroxy-5-ene-steroid dehydrogenase and steroid 5→ 4-ene-isomerase: Purification from mitochondria and kinetic profiles, biophysical characterization of the purified mitochondrial and microsomal enzymes

In human placenta, 3 beta-hydroxy-5-ene-steroid dehydrogenase and steroid 5----4-ene-isomerase, an enzyme complex found in microsomes and mitochondria, synthesizes progesterone from pregnenolone and androstenedione from fetal dehydroepiandrosterone sulfate. The dehydrogenase and isomerase activities of the mitochondrial enzyme were copurified (733-fold) using sequential cholate solubilization, ion exchange chromatography (DEAE-Toyopearl 650S), and hydroxylapatite chromatography (Bio-Gel HT). Enzyme homogeneity was demonstrated by a single protein band in SDS-polyacrylamide gel electrophoresis (monomeric Mr = 41,000), gel filtration at constant specific enzyme activity (Mr = 77,000), and a single NH2-terminal sequence. Kinetic constants were determined for the oxidation of pregnenolone (Km = 1.6 microM, Vmax = 48.6 nmol/min/mg) and dehydroepiandrosterone (Km = 2.4 microM, Vmax = 48.5 nmol/min/mg) and for the isomerization of 5-pregnene-3,20-dione (Km = 9.3 microM, Vmax = 914.2 nmol/min/mg) and 5-androstene-3,17-dione (Km = 27.6 microM, Vmax = 888.4 nmol/min/mg. Mixed substrate studies showed that the dehydrogenase and isomerase activities utilize their respective pregnene and androstene substrates competitively. Dixon analysis demonstrated that the product steroids, progesterone and androstenedione, are competitive inhibitors of the C-21 and C-19 dehydrogenase activities. Enzyme purified from mitochondria and microsomes had similar kinetic profiles with respect to substrate utilization, product inhibition, and cofactor (NAD+) reduction (mean Km +/- SD using C-19 and C-21 dehydrogenase substrates = 26.4 +/- 0.8 microM, mean Vmax = 73.2 +/- 1.3 nmol/min/mg). Pure enzyme from both organelles exhibited identical biophysical properties in terms of molecular weight and subunit composition, pH optima (pH 9.8, dehydrogenase; pH 7.5, isomerase), temperature optimum (37 degrees C), stability in storage and solution, effects of divalent cations, and the single NH2-terminal sequence of 27 amino acids. These results suggest that the mitochondrial and microsomal enzymes are the same protein localized in different organelles.

Human placental 3β-hydroxy-5-ene-steroid dehydrogenase and steroid 5 → 4-ene-isomerase: Purification from microsomes, substrate kinetics, and inhibition by product steroids

In human pregnancy, placental 3 beta-hydroxy-5-ene-steroid dehydrogenase and steroid 5----4-ene-isomerase produce progesterone from pregnenolone and metabolize fetal dehydroepiandrosterone sulfate to androstenedione, an estrogen precursor. The enzyme complex was solubilized from human placental microsomes using the anionic detergent, sodium cholate. Purification (500-fold, 3.9% yield) was achieved by ion exchange chromatography (Fractogel-TSK DEAE 650-S) followed by hydroxylapatite chromatography (Bio-Gel HT). The purified enzyme was detected as a single protein band in sodium dodecylsulfate-polyacrylamide gel electrophoresis (monomeric Mr = 19,000). Fractionation by gel filtration chromatography at constant specific enzyme activity supported enzyme homogeneity and determined the molecular mass (Mr = 76,000). The dehydrogenase and isomerase activities copurified. Kinetic constants were determined at pH 7.4, 37 degrees C for the oxidation of pregnenolone (Km = 1.9 microM, Vmax = 32.6 nmol/min/mg) and dehydroepiandrosterone (Km = 2.8 microM, Vmax = 32.0 nmol/min/mg) and for the isomerization of 5-pregnene-3,20-dione (Km = 9.7 microM, Vmax = 618.3 nmol/min/mg) and 5-androstene-3,17-dione (Km = 23.7 microM, Vmax = 625.7 nmol/min/mg). Mixed substrate analyses showed that the dehydrogenase and isomerase reactions use the appropriate pregnene and androstene steroids as alternative, competitive substrates. Dixon analyses demonstrated competitive inhibition of the oxidation of pregnenolone and dehydroepiandrosterone by both product steroids, progesterone and androstenedione. The enzyme has a 3-fold higher affinity for androstenedione than for progesterone as an inhibitor of dehydrogenase activity. Based on these competitive patterns of substrate utilization and product inhibition, the pregnene and androstene activities of 3 beta-hydroxy-5-ene-steroid dehydrogenase and steroid 5----4-ene-isomerase may be expressed at a single catalytic site on one protein in human placenta.

Endometrial thickness is a valid monitoring parameter in cycles of ovulation induction with menotropins alone

OBJECTIVE To evaluate the ability of an ultrasound (US)-measured periovulatory endometrial thickness to predict conception in hMG-stimulated cycles. DESIGN Retrospective. SETTING A university-based tertiary practice. PATIENTS One hundred twelve patients undergoing 292 cycles of ovulation induction with hMG alone. MAIN OUTCOME MEASURES A periovulatory transvaginal US measurement of endometrial thickness was obtained during cycles of ovulation induction with hMG alone. Clinical pregnancy was defined by fetal cardiac activity. Sensitivity and false-positive rates for multiple discriminatory values of endometrial thickness were calculated and a relative operating characteristic (ROC) curve was constructed to evaluate the performance of this test as a predictor of pregnancy. RESULTS Thirty-eight of 292 cycles resulted in pregnancy. Conception and nonconception cycles showed similar demographics, diagnoses, peak E2, maximum number of follicles, midluteal P, and mean endometrial thickness. Ovulatory dysfunction was a more frequent diagnosis in the conception group. Relative operating characteristic analysis for endometrial thickness as a predictor of pregnancy yielded an area under the curve of 0.623 +/- 0.049 (mean +/- SD). CONCLUSION Endometrial thickness is a valid screening test for conception outcome in cycles stimulated with hMG. A periovulatory endometrial thickness > or = 10 mm defined 91% of conception cycles. No pregnancy occurred when the endometrium measured < 7 mm.

An NADH-induced Conformational Change That Mediates the Sequential 3β-Hydroxysteroid Dehydrogenase/Isomerase Activities Is Supported by Affinity Labeling and the Time-dependent Activation of Isomerase

3β-Hydroxysteroid dehydrogenase (3β-HSD) and steroid Δ-isomerase were copurified as a single protein from human placental microsomes. Because NADH is an essential activator of isomerase (Kact = 2.4 μM, Vmax = 0.6 μmol/min/mg), the affinity alkylating nucleotide, 8-[(4-bromo-2,3-dioxobutyl)thio]adenosine 5′-diphosphate (8-BDB-TADP), was synthesized. 8-BDB-TADP activates isomerase (Kact = 338 μM, Vmax = 2.1 μmol/min/mg) prior to inactivating the enzyme. The inactivation kinetics for isomerase fit the Kitz and Wilson model for time-dependent, irreversible inhibition by 8-BDB-TADP (KI = 314 μM, first order maximal rate constant kobs = 7.8 × 10−3 s−1). NADH (50 μM) significantly protects isomerase from inactivation by 8-BDB-TADP (100 μM). The isomerase activity is inactivated more rapidly by 8-BDB-TADP as the concentration of the affinity alkylator increases from 67 μM (t1/2 = 8.4 min) to 500 μM (t1/2 = 2.4 min). In sharp contrast, the 3β-HSD activity is inactivated more slowly as the concentration of 8-BDB-TADP increases from 67 μM (t1/2 = 4.8 min) to 500 μM (t1/2 = 60.0 min). We hypothesized that the paradoxical kinetics of 3β-HSD inactivation is a consequence of the activation of isomerase by 8-BDB-TADP via a nucleotide-induced shift in enzyme conformation. Biophysical support for an NADH-induced conformational change was obtained using stopped-flow fluorescence spectroscopy. The binding of NADH (10 μM) quenches the intrinsic fluorescence of the enzyme protein in a time-dependent manner (rate constant kapp = 8.1 × 10−3 s−1, t1/2 = 85 s). A time lag is also observed for the activation of isomerase by NADH. This combination of affinity labeling and biophysical data using nucleotide derivatives supports our model for the sequential reaction mechanism; the cofactor product of the 3β-HSD reaction, NADH, activates isomerase by inducing a conformational change in the single, bifunctional enzyme protein.

Site-directed mutagenesis identifies amino acid residues associated with the dehydrogenase and isomerase activities of human type I (placental) 3β-hydroxysteroid dehydrogenase/Isomerase

3beta-hydroxysteroid dehydrogenase/steroid delta5-->4-isomerase (3beta-HSD/isomerase) was expressed by baculovirus in Spodoptera fungiperda (Sf9) insect cells from cDNA sequences encoding human wild-type I (placental) and the human type I mutants - H261R, Y253F and Y253,254F. Western blots of SDS-polyacrylamide gels showed that the baculovirus-infected Sf9 cells expressed the immunoreactive wild-type, H261R, Y253F or Y253,254F protein that co-migrated with purified placental 3beta-HSD/isomerase (monomeric Mr=42,000 Da). The wild-type, H261R and Y253F enzymes were each purified as a single, homogeneous protein from a suspension of the Sf9 cells (5.01). In kinetic studies with purified enzyme, the H261R mutant enzyme had no 3beta-HSD activity, whereas the Km and Vmax values of the isomerase substrate were similar to the values obtained with the wild-type and native enzymes. The Vmax (88 nmol/min/mg) for the conversion of 5-androstene-3,17-dione to androstenedione by the Y253F isomerase activity was 7.0-fold less than the mean Vmax (620 nmol/min/mg) measured for the isomerase activity of the wild-type and native placental enzymes. In microsomal preparations, isomerase activity was completely abolished in the Y253,254F mutant enzyme, but Y253,254F had 45% of the 3beta-HSD activity of the wild-type enzyme. In contrast, the purified Y253F, wild-type and native enzymes had similar Vmax values for substrate oxidation by the 3beta-HSD activity. The 3beta-HSD activities of the Y253F, Y253,254F and wild-type enzymes reduced NAD+ with similar kinetic values. Although NADH activated the isomerase activities of the H261R and wild-type enzymes with similar kinetics, the activation of the isomerase activity of H261R by NAD+ was dramatically decreased. Based on these kinetic measurements, His261 appears to be a critical amino acid residue for the 3beta-HSD activity, and Tyr253 or Tyr254 participates in the isomerase activity of human type I (placental) enzyme.

Estradiol 17β-dehydrogenase and 20α-hydroxysteroid dehydrogenase from human placental cytosol: one enzyme with two activities?

Abstract The soluble enzyme estradiol 17β-dehydrogenase (17β-ED) from human term placental cytosol is reported to be a stereospecific oxidoreductase for estrogen substrates. A published purification scheme (heat treatment and affinity chromatography) yielded a homogeneous protein which had the reported characteristics of pure 17β-ED and also had 20α-hydroxysteroid dehydrogenase (20α-HSD) activity. Spectrophotometric assay when the buffer contained albumin, 8 mg/ml, masked the 20α-HSD activity observed in albumin-free conditions and may explain why this bifunctional activity has gone unrecognized. In human placenta, one enzyme may catalyze stereospecific oxidation/reduction of both estrogen and progesterone.

Postmenopausal ovarian follicle cyst: An unusual cause of estrogen excess

Six years after menopause, a 61-year-old woman complained of enlarging, tender breasts. The serum follicle-stimulating hormone level was 62 mIU/ml; the serum estradiol value was 91 pg/ml; and challenge with progesterone, 100 mg i.m., induced withdrawal bleeding. Histologic examination of a hysterectomy with bilateral salpingo-oophorectomy specimen showed proliferative endometrium and an involuting, luteinized follicle cyst of the left ovary. A follicle cyst causing symptomatic hyperestrogenism after a menopause documented by biochemical tests has not been previously reported.

Therapeutic donor insemination: a prospective randomized study of scheduling methods.

OBJECTIVE To compare basal body temperature (BBT) graphs and urinary luteinizing hormone (LH) monitoring in scheduling therapeutic donor insemination. DESIGN Participants were prospectively randomized to the BBT or LH groups. SETTING Participants were private patients of the Reproductive Endocrine Division at Washington University School of Medicine. PATIENTS Inclusion criteria were designed to assure an isolated male factor. Seventy-four of 113 patients completed the study; 18 had ongoing treatment at the end of the study. INTERVENTIONS Basal body temperature graphs were physician interpreted and appointments prospectively chosen. Luteinizing hormone patients monitored daily urine samples and scheduled an appointment the day after the detected surge. MAIN OUTCOME MEASURES Fecundity rates, cumulative pregnancy rates, and cost per pregnancy were all prospectively evaluated. RESULTS Life table analysis yielded a 6-month cumulative probability of pregnancy of 36.3% in the LH group and 65.1% in the BBT group (P less than 0.025). The total cost per pregnancy was lower in the BBT group (+6,212 versus +3,997; P less than 0.001). CONCLUSIONS This randomized prospective study demonstrates significant therapeutic and economic advantages when therapeutic donor insemination is prospectively scheduled by BBT graphs.

3β-Hydroxysteroid dehydrogenase in human placental microsomes and mitochondria: Co-solubilization of androstene and pregnene activities

3 beta-Hydroxysteroid dehydrogenase (3 beta-HSD) was solubilized from human term-placental microsomes and mitochondria using the non-ionic detergent, polyoxyethylene 20 cetyl ether (BrijR-58). Electron photomicrographs showed microsomes and mitochondria well disrupted by the detergent. The pregnene (C-21) and androstene (C-19) activities co-solubilized over a range (0.04-0.44) of BrijR-58/protein (B/P) concentration ratios (w/w). Optimal solubilization of the C-19 and C-21 activities were 63.3 +/- 2.6% (mean +/- SEM) from mitochondria (B/P ratio 0.37) and 71.8 +/- 2.1% from microsomes (B/P ratio 0.34). Detergent treatment of microsomes and mitochondria--varying time (5-90 min, pH 7.4) or varying pH (6.0-7.8, 90 min)--yielded C-19 activities identical with C-21 activities. The C-21/C-19 specific activity ratios of 3 beta-HSD in particulate, solubilized and chromatographed preparations were 2.28 +/- 0.16 (mean +/- SEM) for mitochondria and 1.97 +/- 0.07 for microsomes. 3 beta-HSD molecular weight estimates were 208,000 (microsomes) and 220,000 (mitochondria). These studies argue that a single protein is responsible for both the C-19 and C-21 activities of 3 beta-HSD and that this protein is the same in microsomes and mitochondria.

Over-expression of human type I (placental) 3β-hydroxy-5-ene-steroid dehydrogenase/isomerase in insect cells infected with recombinant baculovirus

Human type I placental 3 beta-hydroxy-5-ene-steroid dehydrogenase/steroid 5-->4-ene-isomerase (3 beta-HSD/isomerase) synthesizes androstenedione from fetal dehydroepiandrosterone and progesterone from pregnenolone. The full length cDNA that encodes type I 3 beta-HSD/isomerase was inserted into the baculovirus, Autographa californica multiple nucleocapsid polyhedrosis virus, and expressed in Spodoptera fungiperda (Sf-9) insect cells. Western blots showed that the baculovirus-infected Sf-9 cells produced an immunoreactive protein that co-migrated with purified placental 3 beta-HSD/isomerase. Ultracentrifugation localized the expressed enzyme activities in all the membrane-associated organelles of the Sf-9 cell (nuclear, mitochondrial and microsomal). Kinetic studies showed that the expressed enzyme has 3 beta-HSD and isomerase activities. The Michaelis-Menton constant is very similar for the 3 beta-HSD substrate, 5 alpha-androstan-3 beta- ol-17-one, in the Sf-9 cell homogenate (Km = 17.9 microM) and placental microsomes (Km = 16.7 microM). The 3 beta-HSD activity (Vmax = 14.5 nmol/min/mg) is 1.6-fold higher in the Sf-9 cell homogenate compared to placental microsomes (Vmax = 9.1 nmol/min/mg). The Km values are almost identical for the isomerase substrate, 5-androstene-3,17-dione, in the Sf-9 cell homogenate (Km = 14.7 microM) and placental microsomes (Km = 14.4 microM). The specific isomerase activity is 1.5-fold higher in the Sf-9 cells (Vmax = 25.7 nmol/min/mg) relative to placenta (Vmax = 17.2 nmol/min/mg). These studies show that our recombinant baculovirus system over-expresses fully active enzyme that is kinetically identical to native 3 beta-HSD/isomerase in human placenta.