# PLACENTAL 3B-HYDROXYSTEROID DEHYDROGENASE ISOMERASE

> **NIH NIH R01** · WASHINGTON UNIVERSITY · 1993 · $157,810

## Abstract

3beta-Hydroxy-delta 4-5-steroid dehydrogenase (3-HSD) and steroid
delta 4-5-isomerase (isomerase) complex is a rate limiting (due to
3-HSD) regulator of steroid biosynthesis in all mammalian tissues.
In human placenta, it metabolizes fetal androgens to estrogen
precursors and maternal pregnenolone to progesterone.  Since
estrogens stimulate myometrial contractions via prostaglandins and
progesterone relaxes the myometrium, 3-HSD/isomerase may regulate
the initiation of human labor.  3-HSD and isomerase activities for
C-21 (pregnene) and C-19 (androstene) substrates have been
copurified from the microsomes and mitochondria of human term
placenta as a tetramer with monomeric Mr=19,000.  Pregnenolone and
dehydroepiandrosterone competitively inhibit the oxidation of each
other to suggest that the C-21, C-19 3-HSD activities reside at
the same active site.  A pilot affinity alkylation study using the
C-21 product analog 16 alpha-bromoacetoxy-progesterone and
microsomal enzyme suggest that the C19 and C-21 substrates are
modified identically at 2 catalytic sites, one for 3-HSD and one
for isomerase.  This proposal will characterize the microsomal and
the mitochondrial enzymes:  are they the same enzyme localized in
different cell organelles?  Since the enzyme is membrane associated
in vivo, is enzyme in solution identical to enzyme bound to
artificial phospholipid vesicles?  What is the primary structure
determine by a human placental cDNA lambda gt11 library, and
validated by comparison with amino acid sequences analyzed by Edman
degradation?  To understand how the C-19 and C-21 activities of
both 3-HSD and isomerase coexist on one protein, the active site(s)
will be probed with affinity alkylating steroids and cofactors.
Bromoacetoxy analogs of androgen and progestin substrates and
products along with analogs of estrogen inhibitors will be
synthesized to compared inactivation of the 4 enzyme activities,
radioalkylate active site amino acids, and identify peptide regions
which proximate the catalytic center(s).  These studies will
demonstrate the number of catalytic sites responsible for the
activities and how "sister C-19 and C-21 analogs" align within the
active sites(s).  Complementary studies using enzyme generated
alkylators of isomerase (estryne) and 3-HSD (2-methylene-5alpha-
androstan-3 beta-01) affinity alkylators cofactor analogs will
confirm whether the isomerase and dehydrogenase activities reside
at one or separate sites, and the mechanism(s) of this
multiactivity will be explored.  All results will be insights on
the physiological control of the initiation of labor.

## Key facts

- **NIH application ID:** 2197951
- **Project number:** 5R01HD020055-08
- **Recipient organization:** WASHINGTON UNIVERSITY
- **SAM.gov UEI:** L6NFUM28LQM5
- **Principal Investigator:** RONALD C STRICKLER
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 1993
- **Award amount:** $157,810
- **Award type:** 5
- **Project period:** 1985-08-01 → 1994-11-30

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/2197951

## Citation

> US National Institutes of Health, RePORTER application 2197951, PLACENTAL 3B-HYDROXYSTEROID DEHYDROGENASE ISOMERASE (5R01HD020055-08). Retrieved via MORVS 2026-10-25 from https://api.morvs.ai/grant/nih/2197951. Licensed CC0.

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