Document Detail


Human placental 17 beta-estradiol dehydrogenase and 20 alpha-hydroxysteroid dehydrogenase. Studies with 6 beta-bromoacetoxyprogesterone.
MedLine Citation:
PMID:  6571837     Owner:  NLM     Status:  MEDLINE    
Abstract/OtherAbstract:
Two soluble enzyme activities, 17 beta-estradiol dehydrogenase and 20 alpha-hydroxysteroid dehydrogenase, copurified from the cytosol fraction of human term placenta, were identically inactivated by 6 beta-bromoacetoxyprogesterone. This affinity alkylating steroid binds at the enzyme-active site (Km = 866 microM; Vmax = 0.073 mumol/min/mg). Enzyme inactivation by four concentrations of 6 beta-bromoacetoxyprogesterone (molar ratio of steroid to enzyme, 71/1 to 287/1) causes irreversible and time-dependent loss of both the 17 beta- and 20 alpha-activities according to first order kinetics and affirms that the alkylating steroid is an active site-directed inhibitor (KI = 2.7 X 10(-3) M; k3 = 1.6 X 10(-3) s-1). Affinity radioalkylation studies using 6 beta-[2'-14C]bromoacetoxyprogesterone indicate that 2 mol of steroid are bound to each mole of inactivated enzyme dimer (Mr = 68,000). Amino acid analyses of the acid hydrolysate of radioalkylated enzyme show that 6 beta-bromoacetoxyprogesterone carboxymethylates cysteine (56%), histidine (22%), and lysine (8%) residues in the active site. These results are identical with those reported for 2-bromo[2'-14C]acetamidoestrone methyl ether radioalkylation of purified "17 beta-estradiol dehydrogenase." The parallel inactivation of 17 beta-estradiol dehydrogenase and 20 alpha-hydroxysteroid dehydrogenase by 6 beta-bromoacetoxyprogesterone further shows that both activities reside at a single enzyme-active site. The radioalkylation profile supports our proposed model of one enzyme-active site wherein the bound progestin and estrogen substrates are inverted, one relative to the other.
Authors:
J L Thomas; R C Strickler
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Publication Detail:
Type:  Journal Article; Research Support, U.S. Gov't, P.H.S.    
Journal Detail:
Title:  The Journal of biological chemistry     Volume:  258     ISSN:  0021-9258     ISO Abbreviation:  J. Biol. Chem.     Publication Date:  1983 Feb 
Date Detail:
Created Date:  1983-03-17     Completed Date:  1983-03-17     Revised Date:  2007-11-14    
Medline Journal Info:
Nlm Unique ID:  2985121R     Medline TA:  J Biol Chem     Country:  UNITED STATES    
Other Details:
Languages:  eng     Pagination:  1587-90     Citation Subset:  IM    
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MeSH Terms
Descriptor/Qualifier:
17-Hydroxysteroid Dehydrogenases / metabolism*
20-Hydroxysteroid Dehydrogenases / metabolism*
20-alpha-Hydroxysteroid Dehydrogenase
Affinity Labels / pharmacology*
Binding Sites
Estradiol Dehydrogenases / metabolism*
Female
Humans
Hydroxyprogesterones / pharmacology*
Kinetics
Placenta / enzymology*
Pregnancy
Protein Binding
Grant Support
ID/Acronym/Agency:
HD-15903/HD/NICHD NIH HHS
Chemical
Reg. No./Substance:
0/6-bromoacetoxyprogesterone; 0/Affinity Labels; 0/Hydroxyprogesterones; EC 1.1.-/17-Hydroxysteroid Dehydrogenases; EC 1.1.1.-/20-Hydroxysteroid Dehydrogenases; EC 1.1.1.149/20-alpha-Hydroxysteroid Dehydrogenase; EC 1.1.1.62/Estradiol Dehydrogenases

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine


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