title: Inhibitory effects of adenine nucleotides and related substances on UDP-glucuronosyltransferase: structure-effect relationships and evidence for an allosteric mechanism.
abstract: The inhibitory effects of nucleotides and related substances on rat hepatic UDP-glucuronosyltransferase (UGT) were studied. ATP and NADP+ markedly reduced 4-methylumbelliferone (4-MU) UGT activity only when detergent-treated rat liver microsomes were used as the enzyme source. The IC50 values of adenine, ATP, NAD+ and NADP+ were estimated to be below 20 microM, whereas AMP had no inhibitory effect. From the kinetic behavior observed, these adenine-related compounds were assumed to inhibit UGT activity non-competitively without competing with either 4-MU or UDP-glucuronic acid. Among guanine, cytosine and their related nucleotides, only triphosphate nucleotides (CTP and GTP) exhibited potent UGT inhibition, although the effect of GTP was weak. Estradiol 3- and 17-glucuronidation were also inhibited by the inhibitors of 4-MU UGT. The only exception was that estradiol 17-glucuronidation activity was inhibited by AMP (IC50=31 microM). In addition, AMP antagonized the inhibitory effects of adenine, ATP, and NADP+ on 4-MU and estradiol 3- glucuronidation activities. These results suggest that (1) a number of cellular nucleotides present within the endoplasmic reticulum regulate UGT function; and (2) these substances bind to a common allosteric site on UGT to reduce catalytic function.
authors.affiliation: Graduate School of Pharmaceutical Sciences, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582, Japan.
authors.forename: Yoshio
authors.initials: Y
authors.lastname: Nishimura
authors.forename: Shingo
authors.initials: S
authors.lastname: Maeda
authors.forename: Shin-ichi
authors.initials: S
authors.lastname: Ikushiro
authors.forename: Peter I
authors.initials: PI
authors.lastname: Mackenzie
authors.forename: Yuji
authors.initials: Y
authors.lastname: Ishii
authors.forename: Hideyuki
authors.initials: H
authors.lastname: Yamada
mesh_terms: D000227:Adenine Nucleotides / Q000737:chemistry / Q000502:physiology*; D000494:Allosteric Regulation / Q000502:physiology; D000818:Animals; D002460:Cell Line; D014453:Glucuronosyltransferase / Q000037:antagonists & inhibitors* / Q000096:biosynthesis / Q000235:genetics; D006801:Humans; D008297:Male; D008862:Microsomes, Liver / Q000201:enzymology; D051381:Rats; D017208:Rats, Wistar; D013329:Structure-Activity Relationship; D014530:Uridine Diphosphate / Q000737:chemistry / Q000502:physiology
chemical_list: D000227:Adenine Nucleotides; D014530:Uridine Diphosphate; D014453:Glucuronosyltransferase