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Originally published In Press as doi:10.1074/jbc.M210135200 on October 22, 2002
J. Biol. Chem., Vol. 278, Issue 3, 2030-2035, January 17, 2003
Comparative Enzymology of 11 -Hydroxysteroid Dehydrogenase Type
1 from Glucocorticoid Resistant (Guinea Pig) Versus
Sensitive (Human) Species*
Naeem
Shafqat ,
Björn
Elleby§,
Stefan
Svensson§,
Jawed
Shafqat ,
Hans
Jörnvall ,
Lars
Abrahmsen§, and
Udo
Oppermann ¶
From the Department of Medical Biochemistry and
Biophysics, Karolinska Institutet, SE-171 77 Stockholm, Sweden and
§ Biovitrum AB, Department of Assay Development and
Screening and Department of Structural Chemistry, SE-112 76 Stockholm, Sweden
Type 1 11 -hydroxysteroid dehydrogenase
constitutes a prereceptor control mechanism through its ability to
reduce dehydroglucocorticoids to the receptor ligands cortisol and
corticosterone in vivo. We compared kinetic characteristics
of the human and guinea pig 11 -hydroxysteroid dehydrogenase isozymes
derived from species differing in glucocorticoid sensitivity. Both
orthologs were successfully expressed as full-length enzymes in yeast
and COS7 cells and as soluble transmembrane-deleted constructs in
Escherichia coli. Both isozymes display Michaelis-Menten kinetics in intact cells and homogenates and show low apparent micromolar Km values in homogenates, which are
lowered by approximately one order of magnitude in intact cells,
allowing corticosteroid activation at physiological glucocorticoid
levels. Recombinant soluble proteins were expressed and purified with high specific dehydrogenase and reductase activities, revealing several
hundred-fold higher specificity constants than those reported earlier
for the purified native enzyme. Importantly, these purified soluble
enzymes also display a hyperbolic dependence of reaction velocity
versus substrate concentration in 11-oxoreduction
with Km values of 0.8 µM (human) and
0.6 µM (guinea pig), close to the values obtained from
intact cells. Active site titration was carried out with the human
enzyme using a novel inhibitor compound and reveals a fraction of
40-50% active sites/mol total enzyme. The kinetic data obtained argue
against the involvement of 11 -hydroxysteroid dehydrogenase as a
modulating factor for the glucocorticoid resistance observed in guinea
pigs. Instead, the expression of 11 -hydroxysteroid dehydrogenase
type 1 in the Zona glomerulosa of the guinea pig adrenal gland suggests
a role of this enzyme in mineralocorticoid synthesis in this
hypercortisolic species.
*
This work was supported by grants from the NovoNordisk
Foundation, the Swedish Science Council, Biovitrum AB, and Karolinska Institutet.The costs of publication of this
article were defrayed in part by the
payment of page charges. The article
must therefore be hereby marked
"advertisement" in
accordance with 18 U.S.C. Section
1734 solely to indicate this fact.
¶
To whom correspondence should be addressed. Tel.:
46-8-7287680; Fax: 46-8-337462; E-mail: udo.oppermann@mbb.ki.se.
Copyright © 2003 by The American Society for Biochemistry and Molecular Biology, Inc.

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Copyright © 2003 by the American Society for Biochemistry and Molecular Biology.
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