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KMID : 0617319980070010133
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Journal of Pharmacetical Sceiences Ewha Womans University
1998 Volume.7 No. 1 p.133 ~ p.137
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Comparison of Glucuronidating Activity of Two Human cDNAs, UDPGTh1 and UDPGTh2
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Kim, Soon Sun
Owens, Ida S./Sheen, Yhun Yhong
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Abstract
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Two human liver UDP-glucuronosyltransferase cDNA clones, HLUG25 and YDPGTh2 were previously shown to encode isozymes active in the glucuronidation of hyodeoxycholic acid(HDCA) and certain estrogen derivatives (e.g., estriol and 3,4-catechol estrogens), respectively. In this study we have found that the UDPGTh2 encoded isoform (UDPGTh2) and HLUG25-encoded isoform (UDPGTh1) have parallel aglycone specificities. When expressed in COS 1 cells, each isoform metabolized three types of dihydroxy- or trihydroxy-substituted ring structures, including the 3,4-catechol estrogen (4-hydroxyestrone), estriol, 17-epiestriol, and HDCA but the UDPGTh2 isozyme was 100-fold more efficient than UDPGTh1, UDPGTh1 and UDPGTh2 were 86% identical overall (76 differences out of 528 amino acids), including 55 differences in the first 300 amino acids of the amino terminus, a domain which conferred the substrate specificity. The date indicated that a high level of conservation in the amino terminus was not required for the preservation of substrate selectivity. Analysis of glucuronidation activity encoded by UDPGTh1/UDPGTh2 chimeric cDNA constructed at their common restriction sites, Sac 1 (codon 297), Nco 1 (codon 385), and Hha 1 (codon 469), showed that nine amino acids between residues 385 and 469 were important for catalytic efficiency, suggesting that this region represented a domain which was critical for the catalysis but distinct from that responsible for aglycone selection. These date indicate that UDPGTh2 is a primary isoform responsible for the detoxification of the bile salt intermediate as well as the active estrogen intermediates.
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