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PDBsum entry 1dda
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Oxidoreductase
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PDB id
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1dda
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References listed in PDB file
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Key reference
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Title
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Human liver class i alcohol dehydrogenase gammagamma isozyme: the sole cytosolic 3beta-Hydroxysteroid dehydrogenase of iso bile acids.
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Authors
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H.U.Marschall,
U.C.Oppermann,
S.Svensson,
E.Nordling,
B.Persson,
J.O.Höög,
H.Jörnvall.
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Ref.
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Hepatology, 2000,
31,
990-996.
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PubMed id
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Abstract
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3beta-Hydroxy (iso) bile acids are formed during enterohepatic circulation from
3alpha-hydroxy bile acids and constitute normal compounds in plasma but are
virtually absent in bile. Isoursodeoxycholic acid (isoUDCA) is a major
metabolite of UDCA. In a recent study it was found that after administration of
isoUDCA, UDCA became the major acid in bile. Thus, epimerization of the
3beta-hydroxy to a 3alpha-hydroxy group, catalyzed by 3beta-hydroxysteroid
dehydrogenases (HSD) and 3-oxo-reductases must occur. The present study aims to
characterize the human liver bile acid 3beta-HSD. Human liver cytosol and
recombinant alcohol dehydrogenase (ADH) betabeta and gammagamma isozymes were
subjected to native polyacrylamide gel electrophoresis (PAGE) and isoelectric
focusing. Activity staining with oxidized nicotinamide adenine dinucleotide
(NAD(+)) or oxidized nicotinamide adenine dinucleotide phosphate (NADP(+)) as
cofactors and various iso bile acids as substrates was used to screen for
3beta-HSD activity. Reaction products were identified and quantified by gas
chromotography/mass spectrometry (GC/MS). Computer-assisted substrate docking of
isoUDCA to the active site of a 3-dimensional model of human class I gammagamma
ADH was performed. ADH gammagamma isozyme was identified as the iso bile acid
3beta-HSD present in human liver cytosol, with NAD(+) as a cofactor. Values for
k(cat)/K(m) were in the rank order isodeoxycholic acid (isoDCA),
isochenodeoxycholic acid (isoCDCA), isoUDCA, and isolithocholic acid (isoLCA)
(0.10, 0.09, 0.08, and 0. 05 min(-1) x micromol/L(-1), respectively). IsoUDCA
fits as substrate to the 3-dimensional model of the active-site of ADH
gammagamma. ADH gammagamma isozyme was defined as the only bile acid 3beta-HSD
in human liver cytosol. Hydroxysteroid dehydrogenases are candidates for the
binding and transport of 3alpha-hydroxy bile acids. We assume that ADH
gammagamma isozyme is involved in cytosolic bile acid binding and transport
processes as well.
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