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C D King

Publications and source records attributed to C D King.

At least 19 recordsLinked to original sources
PubMed2006

HPLC-NMR with severe column overloading: fast-track metabolite identification in urine and bile samples from rat and dog treated with [14C]-ZD6126.

The subject of this study was the determination of the major urinary and biliary metabolites of [(14)C]-ZD6126 following i.v. administration to female and male bile duct cannulated rats at 10 mg/kg and 20 mg/kg, respectively, and male bile duct cannulated dogs at 6 mg/kg by HPLC-NMR spectroscopy. ZD6126 is a phosphorylated pro-drug, which is rapidly hydrolysed to the active metabolite, ZD6126 phenol. The results presented here demonstrate that [(14)C]-ZD6126 phenol is subsequently metabolised extensively by male dogs and both, male and female rats. Recovery of the dose in bile and urine was determined utilising the radiolabel, revealing biliary excretion as the major route of excretion (93%) in dog, with the majority of the radioactivity recovered in both biofluids in the first 6 h. In the rat, greater than 92% recovery was obtained within the first 24 h. The major route of excretion was via the bile 51-93% within the first 12 h. The administered phosphorylated pro-drug was not observed in any of the excreta samples. Metabolite profiles of bile and urine samples were determined by high performance liquid chromatography with radiochemical detection (HPLC-RAD), which revealed a number of radiolabelled components in each of the biofluids. The individual metabolites were subsequently identified by HPLC-NMR spectroscopy and HPLC-MS. In the male dog, the major component in urine and bile was the [(14)C]-ZD6126 phenol glucuronide, which accounted for 3% and 77% of the dose, respectively. [(14)C]-ZD6126 phenol was observed in urine at 1% of dose, but was not observed in bile. A sulphate conjugate of demethylated [(14)C]-ZD6126 phenol was identified in bile by HPLC-NMR and confirmed by HPLC-MS. In the rat, the bile contained two major radiolabelled components. One was identified as the [(14)C]-ZD6126 phenol glucuronide, the other as a glucuronide conjugate of demethylated [(14)C]-ZD6126 phenol. However, a marked difference in the proportions of these two components was observed between male and female rats, either due to a sex difference in metabolism or a difference in dose level. The glucuronide conjugate of the demethylated [(14)C]-ZD6126 phenol was present at higher concentration in the bile of male rats (4-34%), while the phenol glucuronide was present at higher concentration in the bile of female rats (8-70%) over a 0-6 h collection period. A third component was only observed in the bile samples (0-6 h and 6-12 h) of male rats. This was identified as being the same sulphate conjugate of demethylated [(14)C]-ZD6126 phenol as the one observed in dog bile. The rat urines contained two main metabolites in greatly varying concentrations, namely the demethylated [(14)C]-ZD6126 phenol glucuronide and the glucuronide of [(14)C]-ZD6126 phenol. Again, the differences in relative amounts between male and female rats were observed, the major metabolite in the urines from male rats being the demethylated [(14)C]-ZD6126 phenol (0-17% in 0-24 h), whilst the phenol glucuronide, accounting for 0.5-50% of the dose over 0-24 h, was the major metabolite in females. Methanolic extracts of the pooled biofluid samples were submitted for HPLC-NMR for the quick identification of the major metabolites. Following a single injection of the equivalent of 6-28 ml of the biofluids directly onto the HPLC-column with minimal sample preparation, the metabolites could be largely successfully isolated. Despite severe column overloading, the major metabolites of [(14)C]-ZD6126 could be positively identified, and the results are presented in this paper.

Animals↗
PubMed2003

Differential effects of stress on escape and reflex responses to nociceptive thermal stimuli in the rat.

Acute stress has been shown to increase latencies of nociceptive reflexes, and this effect is considered evidence for stress-induced analgesia. However, tests for nociception that rely on motivated operant escape assess cerebral processing of pain and could be modulated independent of reflex responses. We therefore compared the effects of an acute stressor (restraint) on escape responses and lick/guard reflexes to stimulation of the paws by a thermally regulated floor. Testing sessions included a pre-test exposure to 36 degrees C, followed by a test trial in which either escape from 44 or 36 degrees C or reflex responses to 44 degrees C were observed. Behavioral responses to stress were assessed during a three day period, with baseline testing on day 1, post-stress or control testing on day 2, and evaluation of long-term stress effects on day 3. On day 2, half the animals received 15 min of restraint stress, followed by 15-min pre-test and test trials. Licking and guarding responses to thermal stimulation during 44 degrees C test trials were significantly reduced by restraint stress, confirming previously reported stress effects on nociceptive reflexes. In contrast, learned escape responses to the same thermal stimulus were significantly enhanced after stress. The increase in operant sensitivity suggests that acute restraint, a form of psychological stress, produces hyperalgesia for a level of thermal stimulation that preferentially activates C nociceptors. These results are discussed in relation to studies involving physical or psychological forms of stress, different nociceptive stimuli, and assessment strategies used to evaluate thermal pain sensitivity.

Animals↗
PubMed2000

Consequences of neural asynchrony: a case of auditory neuropathy.

The neural representation of sensory events depends upon neural synchrony. Auditory neuropathy, a disorder of stimulus-timing-related neural synchrony, provides a model for studying the role of synchrony in auditory perception. This article presents electrophysiological and behavioral data from a rare case of auditory neuropathy in a woman with normal hearing thresholds, making it possible to separate audibility from neuropathy. The experimental results, which encompass a wide range of auditory perceptual abilities and neurophysiologic responses to sound, provide new information linking neural synchrony with auditory perception. Findings illustrate that optimal eighth nerve and auditory brainstem synchrony do not appear to be essential for understanding speech in quiet listening situations. However, synchrony is critical for understanding speech in the presence of noise.

Auditory Cortex↗
PubMed2000

UDP-glucuronosyltransferases.

Glucuronidation represents a major pathway which enhances the elimination of many lipophilic xenobiotics and endobiotics to more water-soluble compounds. The UDP-glucuronosyltransferase (UGT) family catalyzes the glucuronidation of the glycosyl group of a nucleotide sugar to an acceptor compound (aglycone) at a nucleophilic functional group of oxygen (eg, hydroxyl or carboxylic acid groups), nitrogen (eg, amines), sulfur (eg, thiols), and carbon, with the formation of a beta-D-glucuronide product. At this time, over 35 different UGT gene products have been described from several different species. UGTs have been divided into two distinct subfamilies based on sequence identities, UGT1 and UGT2. The UGT1 gene subfamily consists of a number of UGTs that result from alternate splicing of multiple first exons and share common exons 2-5. The substrate specificities of the various isoforms have been examined in cultured cell experiments, and include bilirubin, amines, and planar and bulky phenol. The UGT2 gene family is different in that the UGT2 mRNAs are transcribed from individual genes. The UGT2 subfamily consists of numerous enzymes which catalyze the glucuronidation of a diverse chemical base including steroids, bile acids, and opioids. Until recently, the liver has been the major focus for studying the metabolism of xenobiotics and endobiotics. Several groups have identified extrahepatic tissues that express UGT isoforms including the kidney, gastrointestinal tract and brain. This review discusses the two UGT gene families, substrate specificities, and the recent discoveries of UGTs in extrahepatic tissues.

Animals↗
PubMed1999

Expression of UDP-glucuronosyltransferases (UGTs) 2B7 and 1A6 in the human brain and identification of 5-hydroxytryptamine as a substrate.

The extrahepatic expression of UDP-glucuronosyltransferases (UGTs) is important in the detoxification of a number of endogenous and exogenous compounds, including 5-hydroxytryptamine and morphine. Studies were designed to investigate the extrahepatic expression of human UGTs using RT-PCR techniques and to determine the UGTs involved in the glucuronidation of 5-hydroxytryptamine. Human UGT2B7 expression was found in the human liver, kidney, pancreas, and brain, while UGT1A6 expression is found in the liver, kidney, and brain. This is the first observation of UGTs present in the human central nervous system. Using glucuronidation assays, a significant amount of 5-hydroxytryptamine glucuronide was found to be catalyzed by UGT1A6. These studies suggest that UGT2B7 may play an important role in the overall contribution of morphine analgesia by serving to generate the potent morphine-6-O-glucuronide in situ. UGT1A6 could play an important role in the glucuronidation of 5-hydroxytryptamine in vivo, therefore terminating the actions of the neurotransmitter.

Adult↗
PubMed1998

UDP-glucuronosyltransferases in human intestinal mucosa.

While UDP-glucuronosyltransferases (UGTs) are known to be expressed at high levels in human liver, relatively little is known about extrahepatic expression. In the present study, UGT2B family isoforms involved in the glucuronidation of steroid hormones and bile acids have been characterized in microsomes prepared from jejunum, ileum and colon from six human subjects. Glucuronidation of androsterone and testosterone was highly significant and increased from proximal to distal intestine. In contrast, hyodeoxycholic acid was glucuronidated at a low level in jejunum and ileum and activity was barely detectable in colon. No significant glucuronidation of lithocholic acid was found. Small phenols were glucuronidated with much lower activity than found in liver. High levels of UGT protein were detected with polyclonal anti-rat androsterone- and testosterone-UGT antibodies, whereas UGT2B4, a major hepatic hyodeoxycholic acid-specific UGT, was undetectable using a highly specific anti-human UGT2B4 antibody. Screening for RNA expression by RT-PCR confirmed the absence of UGT2B4 and UGT1A6 and showed expression of UGT2B7, a hepatic isoform shown to glucuronidate androsterone, in all intestinal segments. To our knowledge, the presence of functional androsterone and testosterone directed isoforms in human intestine is a novel finding which supports the idea that the intestinal tract functions as a steroid-metabolizing organ and plays a significant role in steroid hormone biotransformation.

Adult↗
PubMed1998

Genetic predisposition to the metabolism of irinotecan (CPT-11). Role of uridine diphosphate glucuronosyltransferase isoform 1A1 in the glucuronidation of its active metabolite (SN-38) in human liver microsomes.

Irinotecan (CPT-11) is a promising antitumor agent, recently approved for use in patients with metastatic colorectal cancer. Its active metabolite, SN-38, is glucuronidated by hepatic uridine diphosphate glucuronosyltransferases (UGTs). The major dose-limiting toxicity of irinotecan therapy is diarrhea, which is believed to be secondary to the biliary excretion of SN-38, the extent of which is determined by SN-38 glucuronidation. The purpose of this study was to identify the specific isoform of UGT involved in SN-38 glucuronidation. In vitro glucuronidation of SN-38 was screened in hepatic microsomes from normal rats (n = 4), normal humans (n = 25), Gunn rats (n = 3), and patients (n = 4) with Crigler-Najjar type I (CN-I) syndrome. A wide intersubject variability in in vitro SN-38 glucuronide formation rates was found in humans. Gunn rats and CN-I patients lacked SN-38 glucuronidating activity, indicating the role of UGT1 isoform in SN-38 glucuronidation. A significant correlation was observed between SN-38 and bilirubin glucuronidation (r = 0.89; P = 0.001), whereas there was a poor relationship between para-nitrophenol and SN-38 glucuronidation (r = 0.08; P = 0.703). Intact SN-38 glucuronidation was observed only in HK293 cells transfected with the UGT1A1 isozyme. These results demonstrate that UGT1A1 is the isoform responsible for SN-38 glucuronidation. These findings indicate a genetic predisposition to the metabolism of irinotecan, suggesting that patients with low UGT1A1 activity, such as those with Gilbert's syndrome, may be at an increased risk for irinotecan toxicity.

Animals↗
PubMed1998

Glucuronidation of catechol estrogens by expressed human UDP-glucuronosyltransferases (UGTs) 1A1, 1A3, and 2B7.

Catechol estrogens are major estrogen metabolites in mammals and are the most potent naturally occurring inhibitors of catecholamine metabolism. These estrogen compounds have been implicated in carcinogenic activity and the 4/2-hydroxyestradiol concentration has been shown to be elevated in neoplastic human mammary tissue compared to normal human breast tissue. Three human liver UDP-glucuronosyltransferases, UGT2B7, UGT1A1, and UGT1A3, have been shown to catalyze the glucuronidation of catechol estrogens and lead to their enhanced elimination via urine or bile. The present study was designed to study the kinetic interaction of expressed human UGT2B7(Y) or (H), UGT1A1, and UGT1A3 toward 2- and 4-hydroxycatechol estrogens. cDNAs encoding UGT2B7(Y) or (H), UGT1A1, and UGT1A3 were expressed in HK293 cells, and cell homogenates or membrane preparations were used to determine their glucuronidation ability. UGT2B7(Y) reacted with higher efficiency toward 4-hydroxyestrogenic catechols, whereas UGT1A1 and UGT1A3 showed higher activities toward 2-hydroxyestrogens. UGT2B7(H) catalyzed estrogen catechol glucuronidation with efficiencies similar to UGT2B7(Y). Flunitrazepam (FNZ), a competitive inhibitor of morphine glucuronidation in hepatic microsomes, competitively inhibited catechol estrogen glucuronidation catalyzed by UGT2B7(Y), UGT1A1, and UGT1A3. Buprenorphine, an opioid substrate that reacts at high efficiency with each of these UGTs, was also studied. FNZ competitively inhibited buprenorphine glucuronidation with UGT1A1 and UGT2B7 but had no inhibitory activity toward UGT1A3. This suggests that buprenorphine and 2-hydroxycatechol estrogens react with separate active sites of UGT1A3. A catecholamine, norepinephrine, did not inhibit UGT2B7(Y)-, UGT1A1-, and UGT1A3-catalyzed glucuronidation of catechol estrogens. These results also suggest that drug-endobiotic interactions are possible in humans and may have implication in carcinogenesis.

Estradiol↗
PubMed1998

The glucuronidation of opioids, other xenobiotics, and androgens by human UGT2B7Y(268) and UGT2B7H(268).

UGT2B7 has been cloned and expressed previously in COS cells and HK293 cells. Two forms have been identified: one with a tyrosine and one with a histidine at position 268. UGT2B7 has been shown to catalyze NSAIDs, catechol estrogens, and morphine-3- and -6-glucuronidation. cDNAs for UGT2B7Y268 and H268 were cloned and stably expressed in HK 293 cells. Studies were designed to test each form for reactivity toward a number of opioid compounds, xenobiotics such as menthol, oxazepam, and propranolol, and androgens such as androsterone and testosterone using membrane preparations derived from HK 293 cells. Both UGT2B7Y and UGT2B7H are highly reactive with many opioids, menthol, androsterone, and (R)- and (S)-propranolol, and similar kinetic values were observed. UGT2B7Y and UGT2B7H react poorly with oxazepam and no difference in (R)- or (S)-glucuronidation rate ratios was found. Thus, UGT2B7Y and H cannot account for the variability in the plasma or urine concentrations of these glucuronides in human populations. Our data suggest that UGT2B7 is a major isoform responsible for the glucuronidation of androsterone. Neither UGT2B7Y nor H catalyzes the glucuronidation of testosterone although each catalyzes the glucuronidation of epitestosterone. UGT2B7 seems to be a major human isoform responsible for the glucuronidation of opioids of the morphinan and oripavine class and is capable of catalyzing the glucuronidation of both the 3- and 6-hydroxyl moieties on these molecules. Thus, UGT2B7 plays a major role in the conversion of morphine to morphine-6-glucuronide, the potent analgesic metabolite of morphine.

Androgens↗
PubMed1998

Glucuronidation of amines and other xenobiotics catalyzed by expressed human UDP-glucuronosyltransferase 1A3.

Glucuronide conjugation of xenobiotics containing a tertiary amine moiety represents a unique and important metabolic pathway for these compounds in humans. Previously, human UDP-glucuronosyltransferase (UGT) 1A4 was shown to be an important enzyme for the formation of quaternary ammonium-linked glucuronides. UGT1A3 is 93% identical to UGT1A4 in primary amino acid sequence. We show that human UGT1A3, transiently expressed in human embryonic kidney 293 cells, also catalyzes the N-glucuronidation of primary, secondary, and tertiary amine substrates, such as 4-aminobiphenyl, diphenylamine, and cyproheptadine. In contrast to expressed human UGT1A4, which catalyzes the glucuronidation of amines with high efficiency, glucuronidation of amines catalyzed by UGT1A3 exhibited low efficiency, suggesting that UGT1A3 makes only a limited contribution to the metabolic elimination of these compounds. The reactivity of expressed human UGT1A3 toward hydroxylated and carboxylic acid-containing compounds was also examined. In addition to amines, expressed human UGT1A3 catalyzed the glucuronidation of opioids (e.g. morphine and buprenorphine), coumarins, flavonoids (e.g. naringenin and quercetin), anthraquinones, and small phenolic compounds (e.g. 4-nitrophenol). Drugs containing a carboxylic acid moiety, such as nonsteroidal anti-inflammatory agents (e.g. naproxen and ibuprofen) and fibrates (e.g. ciprofibrate), were substrates for human UGT1A3. In contrast, compounds containing an aliphatic hydroxyl group, such as sapogenins, monoterpenoid alcohols (e.g. menthol and borneol), and androgens, were not conjugated by expressed human UGT1A3. Of the compounds tested, scopoletin, naringenin, and norbuprenorphine appeared to be the best xenobiotic substrates for human UGT1A3.

Amines↗
PubMed1998

Immunohistochemical localization of UDP-glucuronosyltransferases in rat brain during early development.

Extrahepatic glucuronidation, such as that in the central nervous system (CNS), may play a very important role in xenobiotic disposition and may serve to protect the CNS from potentially toxic xenobiotics. UDP-glucuronosyltransferase (UGT) 1A6 is an important catalyst for phenol and polycyclic aromatic hydrocarbon glucuronidation. Studies were designed to determine the immunohistochemical localization of UGT1A6 and the steroid-reactive UGTs 2B2 and 2B3 in brain regions throughout the rat development. Neuronal cells, such as pyramidal cells, in sections from cerebral cortex and hippocampus displayed intensive UGT1A6-specific staining. UGT1A6-specific staining was also found in neuronal cells throughout the cerebral cortex, as well as in the cerebellar white matter. Glial cells revealed no apparent staining. In addition, staining for UGT1A6 was seen in choroid plexus at a later developmental stage. Although UGT1A6 staining was evident, brain sections analyzed for UGT2B2 and UGT2B3 immunoreactivity showed no significant staining. These results provide the first definitive evidence for the presence and cellular localization of UGT1A6, in neurons of developing rat brain, whereas UGT2B2 and UGT2B3 were not detected.

Animals↗
PubMed1997

Human UGT2B7 catalyzes morphine glucuronidation.

A human UDP-glucuronosyltransferase (UGT) catalyzing the glucuronidation of morphine has been identified. A full length cDNA was isolated from a human liver cDNA library and found to be identical to the UGT2B7 form having a tyrosine at position 288. This cDNA was transfected into HK 293 cells, and stable expression was achieved. Cell homogenates and membrane preparations from HK 293 cells expressing UGT2B7 catalyzed the glucuronidation of morphine and other clinically significant opioid agonists, antagonists, and partial agonists. UGT2B7 catalyzed morphine glucuronidation at the 3- and 6-hydroxy positions and also mediated the formation of codeine-6-glucuronide from codeine. This represents the first demonstration of a UGT capable of catalyzing the glucuronidation of both the 3- and 6-positions of opioids. Since humans excrete morphine-3-glucuronide and morphine-6-glucuronide after morphine administration, it is likely that UGT2B7 is a major isoform in humans responsible for the metabolism of this important drug and its surrogates.

Cell Line↗
PubMed1997

Comparison of stably expressed rat UGT1.1 and UGT2B1 in the glucuronidation of opioid compounds.

Opioids are important drugs used as analgesics, antitussives, antidiarrheals, and in the therapy of myocardial infarctions, and as antagonists of opioid intoxication. The glucuronidation of these compounds, catalyzed by UDP-glucuronosyltransferases (UGTs), is well known to be a primary step in their metabolism to hydrophilic products and in their ultimate excretion. The present study was designed to compare the reactivity and relative glucuronidation efficiencies of opioid agonists, antagonists, and partial agonists with two rat UGT isoforms; UGT1.1, which is generally considered the "bilirubin UGT," and UGT2B1, which has previously been shown to catalyze the glucuronidation of testosterone, chloramphenicol, and (-)-morphine. Rat UGT2B1, stably expressed in HK293 cells, exhibited high glucuronidation rates and catalytic efficiencies for many opioids, although values for (-)-morphine and nalorphine were the highest. In contrast, these compounds were very poor substrates for expressed rat UGT1.1. Comparably high glucuronidation rates and efficiencies were found for buprenorphine and diprenorphine with both UGT isoforms. These results suggest that opioids with morphinan-based chemical structures similar to (-)-morphine interact with UGTs differently than those with oripavine-based chemical structures similar to buprenorphine. To investigate the contribution of rat UGT1.1 and UGT2B1 in the overall rate of glucuronidation of buprenorphine in the rat liver, hepatic microsomes from Gunn rats (where UGT1.1 activity is absent) and Wistar rats (where UGT1.1 activity is present) were studied. Buprenorphine glucuronidation activity in Gunn rat liver microsomes exhibit approximately 25% of rates observed in Wistar rat liver microsomes, whereas (-)-morphine, naloxone, and naltrexone glucuronidation rates were not significantly different in microsomal preparations from Gunn and Wistar rats. These data suggest that UGT2B1 is the major hepatic enzyme involved in the glucuronidation of (-)-morphine and naloxone in livers from untreated rats, whereas buprenorphine glucuronidation is preferentially catalyzed by rat UGT1.1.

Analgesics, Opioid↗
PubMed1997

Glucuronidation of retinoids by rat recombinant UDP: glucuronosyltransferase 1.1 (bilirubin UGT).

Rat liver recombinant BR1UGT1.1 was found to have significant activity toward retinoid substrates. UGT1.1 glucuronidation activity was 91 +/- 18 pmol/mg x min for atRA and 113 +/- 19 pmol/mg x min for 5,6-epoxy-atRA. The apparent K(M) and V(max) of atRA acid glucuronidation by UGT1.1 were 59.1 +/- 5.4 microM and 158 +/- 43 pmol/mg x min, respectively. SDS-PAGE and Western blot analysis of UGT1.1-transfected HK293 membrane proteins photolabeled with [11,12-3H]atRA revealed a protein of approximately 56 kDa that was labeled by [3H]atRA, detected by anti-pNP UGT antibody and not present in membranes from nontransfected HK293 cells. Liver microsomes from Gunn rats, which lack UGT1.1, had significant activity toward atRA (111 +/- 28 pmol/mg x min).

Affinity Labels↗
PubMed1996

The glucuronidation of exogenous and endogenous compounds by stably expressed rat and human UDP-glucuronosyltransferase 1.1.

Rat and human UDP-glucuronosyltransferase (UGT) 1.1 share > 70% identity in their deduced primary amino acid sequences. We have previously shown that rat UGT1.1, stably expressed in human embryonic kidney 293 cells, catalyzes the glucuronidation of bilirubin and the mixed opioid agonist/antagonist buprenorphine with high efficiency. The present study was designed to characterize the reactivity of expressed human UGT1.1 with opioid compounds and compare its substrate specificity for opioids to that of the expressed rat enzyme. The results show that both rat and human UGT1.1 catalyze the glucuronidation of opioids with a relative reactivity of buprenorphine > > nalorphine approximately naltrexone. Comparison of glucuronidation activities in livers from Crigler-Najjar type 1 patients and normal patients indicates that UGT1.1 catalyzes at least 75% of buprenorphine conjugation in normal human liver. In separate studies, the reactivity of expressed rat UGT1.1 was characterized toward various xeno-and endobiotics of various compound classes. It was found that both rat and human UGT1.1 exhibited comparable substrate specificities and efficiencies (Vmax/Km) of glucuronide formation for anthraquinones, coumarins, estrogens, flavonoids, and phenolic compounds. Neither rat nor human UGT1.1 catalyzed the glucuronidation of amines, monoterpenoid alcohols, androgens, or progestins. In general, these data indicate that rat and human UGT1.1 are functionally identical and can be considered orthologous enzymes.

Animals↗
PubMed1995

Cloning and stable expression of a cDNA encoding a rat liver UDP-glucuronosyltransferase (UDP-glucuronosyltransferase 1.1) that catalyzes the glucuronidation of opioids and bilirubin.

A chicken anti-rat polyclonal antibody to a purified rat liver UDP-glucuronosyltransferase (UGT) with catalytic activity toward opioid substrates was used to screen a liver cDNA library prepared from phenobarbital-treated Wistar rats. A number of positive clones were obtained, and one of these clones, pM1, was further characterized. Clone pM1 was found to be a full length cDNA coding for a member of the rat UGT1 gene family. Specifically, pM1 represents the full length homologue of the Gunn rat liver pseudo-gene product UGT1.1P and, therefore, has been designated UGT1.1r. The cDNA insert has an open reading frame of 1605 base pairs, which codes for a protein of 535 amino acids and is flanked by 2 and 632 base pairs of 5' and 3' noncoding sequence, respectively. The deduced amino acid sequence of pM1 contains amino acid sequences identical to the amino-terminal and internal peptides of the purified rat liver opioid UGT and to sequences reported for a rat liver bilirubin UGT [FEBS Lett. 299:183-186 (1992)]. Stable expression of UGT1.1r in human embryonic kidney 293 cells showed that a protein with a subunit molecular mass (56 kDa) identical to that of the purified protein was produced. Expressed UGT1.1r protein catalyzed the glucuronidation of buprenorphine and bilirubin at high rates. Other opioids, such as nalorphine and morphine, were also substrates for the expressed UGT1.1r protein. These results show that bilirubin and opioids can be conjugated by the same rat liver UGT.

Amino Acid Sequence↗
PubMed1994

Allele specific inactivation of insulin 1 and 2, in the mouse yolk sac, indicates imprinting.

Genomic imprinting, gene inactivation during gametogenesis, causes maternal and paternal alleles of some genes to function unequally. We examined the possibility of imprinting in insulin genes because the human insulin gene (ins) and its mouse homologue (ins2) are adjacent to the known imprinted genes, igf2 and H19, and because imprinting has been implicated in the transmission of an ins linked risk for Type I diabetes. We show, by single strand conformational polymorphism (SSCP) analysis of cDNAs from parents and progeny of interspecies mouse crosses, that insulin genes are imprinted. While both alleles of the two mouse insulin genes were active in embryonic pancreas, only paternal alleles for both genes were active in the yolk sac.

Alleles↗