UDP-glucosyltransferase Activity Research Articles

Transcriptome analysis reveals the effects of hydrogen gas on NaCl stress in purslane roots

Purslane development may be affected by high salt concentrations. It has been found that H2 enhanced salt-tolerance of plant. The goal of present study was to investigate the impact of H2 on root growth of purslane under salt stress, and to analyze the molecular mechanism of H2 effect on salt tolerance of purslane by using transcriptome method. Under hydroponic conditions, H2 significantly reduced electrolyte leakage and malondialdehyde content, substantially enhance the activities of superoxide dismutase, peroxidase, catalase and ascorbate peroxidase in roots of purslane (‘Tall Green’) under NaCl stress. Transcriptome analysis showed that NaCl stress significantly affected the expression of differential genes in purslane roots. The expression of differential genes was significantly affected by the addition of H2, especially under salt stress. The qRT-PCR analysis was used to confirm the RNA-seq results. GO and KEGG analysis showed that the DEGs were mainly involved in metabolism of reactive oxygen species (ROS), plant hormone signal transduction and UDP-glucosyltransferase activity. At the transcriptional level, ROS accumulation and clearance; auxin, cytokinin, gibberellin, abscisic acid signal transduction; sucrose synthesis and catabolism, and the synthesis of plant cell wall component may play a crucial role in the influence of H2 on the salt tolerance of purslane. These findings have crucial implications for improved understanding the role of H2 in plant salt tolerance and provide specific data for in-depth identification of purslane salt tolerance genes.

Inhibition of human UDP-glucuronosyltransferase enzyme by ripretinib: Implications for drug-drug interactions

Ripretinib, a tyrosine kinase inhibitor (TKI), is the first FDA approved fourth-line therapy for adults with advanced gastrointestinal stromal tumor (GIST). Studies have shown that several TKIs for treating GIST were potent inhibitors of human UDP-glucosyltransferase (UGTs) enzymes. However, whether ripretinib affects the activity of UGTs remains unclear. The aim of this study was to investigate the effects of ripretinib on major UGT isoforms, as well as to evaluate its potential drug-drug interactions (DDIs) risk caused by the inhibition of UGTs activities. The inhibitory effects and inhibition modes of ripretinib on UGTs were systematically evaluated using high-performance liquid chromatography (HPLC) and enzyme kinetic studies, respectively. Our data showed that ripretinib exhibited potent inhibition against UGT1A1, UGT1A3, UGT1A4, UGT1A7 and UGT1A8. Enzyme kinetic studies indicated that ripretinib was not only a competitive inhibitor of UGT1A1, UGT1A4 and UGT1A7, but also a noncompetitive inhibitor of UGT1A3, as well as a mixed inhibitor of UGT1A8. The prediction results of in vitro-in vivo extrapolation (IVIVE) demonstrated that ripretinib might bring the potential risk of DDIs when combined with substrates of UGT1A1, UGT1A3, UGT1A4, UGT1A7 or UGT1A8. Therefore, special attention should be paid when ripretinib is used in conjunction with other drugs metabolized by UGTs to avoid risk of DDIs in clinic.

Natural alleles of a uridine 5'-diphospho-glucosyltransferase gene responsible for differential endosperm development between upland rice and paddy rice.

Traditional upland rice generally exhibits insufficient grains resulting from abnormal endosperm development compared to paddy rice. However, the underlying molecular mechanism of this trait is poorly understood. Here, we cloned the uridine 5'-diphospho (UDP)-glucosyltransferase gene EDR1 (Endosperm Development in Rice) responsible for differential endosperm development between upland rice and paddy rice by performing quantitative trait loci analysis and map-based cloning. EDR1 was highly expressed in developing seeds during grain filling. Natural variations in EDR1 significantly reduced the UDP-glucosyltransferase activity of EDR1YZN compared to EDR1YD1 , resulting in abnormal endosperm development in the near-isogenic line, accompanied by insufficient grains and changes in grain quality. By analyzing the distribution of the two alleles EDR1YD1 and EDR1YZN among diverse paddy rice and upland rice varieties, we discovered that EDR1 was conserved in upland rice, but segregated in paddy rice. Further analyses of grain chalkiness in the alleles of EDR1YD1 and EDR1YZN varieties indicated that rice varieties harboring EDR1YZN and EDR1YD1 preferentially showed high chalkiness, and low chalkiness, respectively. Taken together, these results suggest that the UDP-glucosyltransferase gene EDR1 is an important determinant controlling differential endosperm development between upland rice and paddy rice.

Identification of potential genes involved in triterpenoid saponins biosynthesis in Gleditsia sinensis by transcriptome and metabolome analyses

Gleditsia sinensis is widely used as a medicinal plant in Asia, especially in China. Triterpenes, alkaloids, and sterols were isolated from Gleditsia species. Among them, triterpenoid saponins are very important metabolites owing to their various pharmacological activities. However, the triterpenoid saponin biosynthesis pathway has not been well characterized. In the present study, we performed de novo transcriptome assembly for 14.3 Gbps of clean reads sequenced from nine tissues of G. sinensis. The results showed that 81,511 unique transcripts (unitranscripts) (47,855 unigenes) were constructed, of which 31,717 unigenes were annotated with Gene Ontology and EC numbers by Blast2GO against the NCBI-nr protein database. We also analyzed the metabolite contents in the same nine tissues by LS–MS/MS, and saponins including gleditsioside I were found in fruit at higher levels. Many of the genes with tissue-specific expression in fruit are involved in the flavonoid biosynthesis pathway, and many of those have UDP-glucosyltransferase (UGT) activity. We constructed a saponin biosynthesis pathway and identified two key enzyme families in the triterpenoid saponin biosynthesis pathway, cytochrome P450 and UDP-glucosyltransferase, that are encoded by 37 unigenes and 77 unigenes, respectively. CYP72A, CYP716A, and CYP88D, which are known as key enzymes for saponin biosynthesis, were also identified among the P450s. Our results provide insight into the secondary metabolite biosynthesis and serve as important resources for future research and cultivation of G. sinensis.

In vitro analysis of DIMBOA catabolism in the Asian corn borer Ostrinia furnacalis (Lepidoptera: Crambidae)

Larvae of the Asian corn borer Ostrinia furnacalis (Guenee) must cope with 2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one (DIMBOA), a major toxic allelochemical present in its host plant, maize Zea mays L. UDP-glucosyltransferase (UGT), which conjugates glucose to various lipophilic toxic compounds and thereby makes them more hydrophilic for easier excretion, has been suggested to be involved in the detoxification of DIMBOA in several insects. Our previous in vitro assays using O. furnacalis midgut homogenates demonstrated that DIMBOA was catabolized only when UDP-glucose, a glucose donor for UGT activity, was included in the reaction mixture; however, DIMBOA glucoside, the expected product of UGT activity, was only detected in trace amounts in assay products. The present study revealed that DIMBOA glucoside was produced, but was immediately degraded by unidentified enzymes in the midgut homogenate that do not require UDP-glucose for their activities, suggesting the presence of a novel route for DIMBOA catabolism in O. furnacalis.

Two UGT84 Family Glycosyltransferases Catalyze a Critical Reaction of Hydrolyzable Tannin Biosynthesis in Pomegranate (Punica granatum).

Hydrolyzable tannins (HTs) play important roles in plant herbivore deterrence and promotion of human health. A critical step in HT production is the formation of 1-O-galloyl-β-D-glucopyranoside (β-glucogallin, ester-linked gallic acid and glucose) by a UDP-glucosyltransferase (UGT) activity. We cloned and biochemically characterized four candidate UGTs from pomegranate (Punica granatum), of which only UGT84A23 and UGT84A24 exhibited β-glucogallin forming activities in enzyme assays. Although overexpression and single RNAi knockdown pomegranate hairy root lines of UGT84A23 or UGT84A24 did not lead to obvious alterations in punicalagin (the prevalent HT in pomegranate) accumulation, double knockdown lines of the two UGTs resulted in largely reduced levels of punicalagins and bis-hexahydroxydiphenyl glucose isomers. An unexpected accumulation of galloyl glucosides (ether-linked gallic acid and glucose) was also detected in the double knockdown lines, suggesting that gallic acid was utilized by an unidentified UGT activity for glucoside formation. Transient expression in Nicotiana benthamiana leaves and immunogold labeling in roots of pomegranate seedlings collectively indicated cytosolic localization of UGT84A23 and UGT84A24. Overall, functional characterization and localization of UGT84A23 and UGT84A24 open up opportunities for further understanding the regulatory control of HT metabolism in plants and its coordination with other biochemical pathways in the metabolic network.

Stimulation of Rg3 ginsenoside biosynthesis in ginseng hairy roots elicited by methyl jasmonate

It has been recognized that ginsenoside Rg3 is not naturally produced in ginseng although this ginsenoside can accumulate in red ginseng as the result of a thermal process. In order to determine whether or not Rg3 is synthesized in ginseng, hairy roots were treated with methyl jasmonate (MJ). From HPLC analysis, no peak for Rg3 was observed in the controls. However, Rg3 did accumulate in hairy roots that were MJ-treated for 7 days. Rg3 content was 0.42 mg/g (dry weight). To gain more insight into the effects of MJ on UDP-glucosyltransferase (UGT) activity, we attempted to evaluate ginsenoside Rg3 biosynthesis by UGT. A new peak for putative Rg3 was observed, which was confirmed by LC-MS/MS analysis. Our findings indicate that the proteins extracted from our hairy root lines can catalyze Rg3 from Rh2. This suggests that our ginseng hairy root lines possess Rg3 biosynthesis capacity.

Detoxification and Transcriptome Response in Arabidopsis Seedlings Exposed to the Allelochemical Benzoxazolin-2(3H)-one

Benzoxazolin-2(3H)-one (BOA) is an allelochemical most commonly associated with monocot species, formed from the O-glucoside of 2,4-dihydroxy-2H-1,4-benzoxazin-3(4H)-one by a two-step degradation process. The capacity of Arabidopsis to detoxify exogenously supplied BOA was analyzed by quantification of the major known metabolites BOA-6-OH, BOA-6-O-glucoside, and glucoside carbamate, revealing that detoxification occurs predominantly through O-glucosylation of the intermediate BOA-6-OH, most likely requiring the sequential action of as-yet-unidentified cytochrome P450 and UDP-glucosyltransferase activities. Transcriptional profiling experiments were also performed with Arabidopsis seedlings exposed to BOA concentrations, representing I(50) and I(80) levels based on root elongation inhibition assays. One of the largest functional categories observed for BOA-responsive genes corresponded to protein families known to participate in cell rescue and defense, with the majority of these genes potentially associated with chemical detoxification pathways. Further experiments using a subset of these genes revealed that many are also transcriptionally induced by a variety of structurally diverse xenobiotic compounds, suggesting they comprise components of a coordinately regulated, broad specificity xenobiotic defense response. The data significantly expand upon previous studies examining plant transcriptional responses to allelochemicals and other environmental toxins and provide novel insights into xenobiotic detoxification mechanisms in plants.

A novel glucosyltransferase involved in steroid saponin biosynthesis in Solanum aculeatissimum

Steroidal saponins are widely distributed in many plant species. Their diverse structures have resulted in a wide range of applications, including drug and medicine production. It has been suggested that the nature of the non-saccharide and oligosaccharide portions of the saponin molecule both contribute to the properties of individual saponins. Despite numerous studies on the occurrence, chemical structure, and varying pharmaceutical activities of steroidal saponins, their biosynthesis pathway is poorly understood. Glycosylation is thought to be the final step in steroidal saponin biosynthesis and it is thought to be involved in regulating the biological activities of saponins. Isolation of the glycosyltransferases that catalyze the transfer of sugar molecules to steroidal compounds will help to clarify the mechanisms that produce diverse saponins and control their activities in plants. In this study, we obtained three cDNAs encoding putative glycosyltransferases from Solanum aculeatissimum. One of the three, SaGT4A showed UDP-glucosyltransferase activity. This is the first cloned glucosyltransferase involved in steroidal saponin biosynthesis. SaGT4A catalyzes the 3-O-glucosylation of steroidal sapogenins, such as diosgenin, nuatigenin, and tigogenin. This enzyme also glucosylates steroidal alkaloids, such as solanidine, solasodine, and tomatidine. Gene expression analysis revealed that the accumulation of SaGT4A transcripts showed a unique response to wounding stress indicating the involvement of SaGT4A in plant defense system.

An entomopoxvirus and a granulovirus use different mechanisms to prevent pupation of Adoxophyes honmai

Adoxophyes honmai larvae inoculated with 10× the 95% lethal concentration of an entomopoxvirus (AdhoEPV) did not pupate, underwent a prolonged larval stage, and died during their final instar, unlike non-infected larvae which pupated after five larval instars. In previous work we showed that a granulovirus (AdhoGV) also retarded host development and prevented pupation of A. honmai larvae. In this study, endocrinological alterations in AdhoEPV-infected larvae were compared to those in AdhoGV-infected larvae. AdhoEPV-infected larvae had no peak of juvenile hormone (JH) esterase activity during the final instar, suggesting that JH titers in virus-infected larvae remained high during this period. In AdhoEPV-infected larvae the ecdysteroid titer remained low during the final instar, whereas in AdhoGV-infected larvae it peaked during the final instar and remained high towards the later stages of this instar. Ecdysteroid UDP-glucosyltransferase (EGT) activity was detected in the hemolymph of AdhoGV-infected A. honmai larvae, suggesting that the ecdysteroid would be inactivated in these insects. No EGT activity was detected in the hemolymph of either AdhoEPV-infected or non-infected A. honmai larvae. Thus, while AdhoEPV and AdhoGV both prevent pupation of A. honmai larvae, the mechanisms by which they do so appear to be different.

Sequential NO Production by Mitochondria and Endoplasmic Reticulum during Induced Apoptosis

Early stages of rat thymocyte apoptosis measured as annexin-V positive events and induced by methylprednisolone (MPS), etoposide, and thapsigargin, showed a sequential increase in nitric oxide (NO) production by mitochondrial and endoplasmic reticulum membranes. Thapsigargin induced the highest NO production, a sevenfold increase as compared with untreated thymocytes, in mitochondrial and microsomal membranes. MPS and etoposide were equally effective in increasing NO production by mitochondrial membranes by a factor of 4–5, with only a slight increase in NO production by endoplasmic reticulum membranes. Western blot analysis of both types of membrane indicated that a nitric oxide synthase (NOS) isoenzyme is present in mitochondrial membranes and reacts with antibodies to i-NOS (type II), while reactivity to antibodies to e-NOS (type III) was restricted to endoplasmic reticulum. The participation of endoplasmic reticulum during apoptosis was further determined by alterations in UDP-Glucosyltransferase (UDP-GT) and NADPH cytochrome P450 reductase. Increased UDP-GT activity was observed after thapsigargin treatment, and no changes were found after treatment with etoposide or MPS. NADPH cytochrome P450 reductase activity markedly decreased during apoptosis, being stronger after thapsigargin treatment. The latest stage of the apoptotic process was measured by caspase activities. Caspase 3 activity was markedly increased by the three apoptosis inducers; caspase 6 was only activated by MPS and etoposide, while caspase 8 was not activated by any of these inducers. It is clear that mitochondria and endoplasmic reticulum are involved in thapsigargin induced thymocyte apoptosis. Meanwhile, other thymocyte apoptotic pathways, such as those induced by MPS or etoposide, seem to centrally involve mitochondria but not endoplasmic reticulum.

Phenobarbital Induction of UDP-glucosyltransferase Activity in Drosophila melanogaster Meigen

The inducibility of UDP-glucosyltransferase activities towards the exogenous substrates 1-naphthol and 2-naphthol and the endogenous metabolite xanthurenic acid was demonstrated in Drosophila melanogaster Meigen larvae and adults using phenobarbital as an inducer. In adults, a 3.5-fold increase of glucosyltransferase activity toward xanthurenic acid and a 2.0-fold increase of the activity toward exogenous substrates (1-naphthol and 2-naphthol) was found. In larvae, maximum induction of all three UDP-glucosyltransferase activities (2.5-fold and 1.5-fold increase of the activity toward the exogenous and endogenous substrates, respectively) was achieved when insects, reared on solid medium, were exposed to phenobarbital for 24 h. However, a 24-h exposure to inducer on liquid medium yielded the same level of induction as in solid medium only for xanthurenic acid:UDP-glucosyltransferase activity. Repression of the activities toward exogenous substrates also was noticed. On this medium, comparable induction to that detected on solid medium was found when inducer exposure was reduced to 2.5 h. According to the observed variation resulting from the different conditions of phenobarbital treatment, a differential induction of UDP-glucosyltransferase isoenzymes also was demonstrated. After 2.5 h of inducer exposure, three isoenzymes (every one specific for each of the three analysed substrates) were detected; whereas, after 24 h of inducer treatment, only one isoenzyme, specific for xanthurenic acid, was detected.

Oral bioavailability and pharmacokinetics of elimination of 9-hydroxybenzo[a]pyrene and its glucoside and sulfate conjugates after administration to male and female American lobsters, Homarus americanus.

The pharmacokinetics of [(3)H]-9-hydroxybenzo[a]pyrene (9-OH-BaP), a highly lipophilic primary metabolite of benzo(a)pyrene, were examined after intrapericardial (iv) or oral doses of 50 or 200 microg/kg to intermolt American lobsters, Homarus americanus. Combining data for all lobsters, the average terminal elimination half-life of parent 9-OH-BaP was 97.3 h after iv and 56.5 h after oral administration, considerably less than found previously for benzo(a)pyrene (720 h). The oral bioavailability of parent 9-OH-BaP, calculated from the area under the hemolymph concentration curve, was 15.9%. The low bioavailability and variable elimination rates were attributed to extensive first-pass conjugation and sequestration in the hepatopancreas. BaP-9-sulfate was the major metabolite. Hemolymph concentrations of BaP-9-sulfate increased up to one day after the dose, and then decreased, with a terminal elimination half-life of 45 h. BaP 9-beta-D-glucoside was a minor metabolite in most hemolymph and tissue samples; an exception was hemolymph from the iv high-dose group. Concentrations of 9-OH-BaP and metabolites in the edible muscle tissue were similar to those in hemolymph, and 9-OH-BaP residues at 10 to 16 days after the dose were 3 to 12 ng/g muscle. Sulfotransferase and UDP-glucosyltransferase (UGT) activities with 9-OH-BaP were found in the antennal gland, intestinal mucosa, and hepatopancreas (UGT only). Sulfatase activity with BaP-9-sulfate, found in both the hepatopancreas and the antennal gland, was thought to contribute to metabolite cycling. These studies showed that 9-OH-BaP was readily conjugated to sulfate and glucose in the lobster, and that despite their high lipophilicity, 9-OH-BaP and conjugates were excreted from the lobster hemolymph and tissues much more rapidly than benzo[a]pyrene.

The oral bioavailability, pharmacokinetics and biotransformation of 9-hydroxybenzo[a]pyrene in the American lobster, Homarus americanus

The pharmacokinetics of [ 3H]-9-hydroxy-benzo[a]pyrene (9-OH-BaP) were examined after single intrapericardial (IV) or oral doses to intermolt American lobsters, Homarus americanus. A three-compartment model best described the disposition of parent 9-OH-BaP in the hemolymph after IV administration. The major metabolite found in hemolymph 8 h after administration, BaP 9-sulfate, reached its peak concentration at one day after the dose. BaP 9-sulfate was eliminated from hemolymph more rapidly than 9-OH-BaP or BaP9-β-D-glucoside, which were present in all hemolymph samples at all times. The oral bioavailability (F) for 9-OH-BaP, estimated from the area under concentration-time curve (AUC), ranged from 3.4 to 14.3%. In all treated lobsters, < 10% dose was left in tissues at 10 days. PAPS-sulfotransferase (ST) and UDP-glucosyltransferase (UDP-GT) activities were detected in the intestinal mucosa as well as in the antennal gland (ST) and the hepatopancreas (UDP-GT). These studies showed that 9-OH-BaP and its sulfate and glucoside conjugates were excreted from lobster tissues more rapidly than BaP, but were retained by the lobster for longer than the smaller, less lipophilic phenolic compounds, phenol and β-naphthol and their metabolites.

Separation by FPLC chromatofocusing of UDP-glucosyltransferases from three developmental stages of Drosophila melanogaster.

Variation of UDP-glucosyltransferase activity, during Drosophila melanogaster development, was analyzed. The endogenous metabolite xanthurenic acid and the xenobiotic compounds 1-naphthol and 2-naphthol were used as substrates. Developmentally regulated differences were observed for the three substrates, suggesting the presence of UDP-glucosyltransferase isoenzymes. This was further confirmed by FPLC chromatofocusing on a Mono P column: seven peaks of UDP-glucosyltransferase activity (pHs: > or = 6.3, 5.8, 5.5, 4.9, 4.5, 4.2, < or = 4.0) with either single or overlapping substrate specificity were detected. A single xanthurenic acid:UDP-glucosyltransferase activity (pl 5.8) was found throughout development. In contrast, a gradual increase in the number of 2-napthol:UDP-glucosyltransferase-isoenzymes (pl from 6.3 to 4.0) was observed during development, whereas no isoenzymes specific for 1-naphthol were resolved. Based on the distribution and substrate specificity of the eluted peaks in the three developmental stages analyzed, the presence of seven or possibly eight UDP-glucosyltransferase isoenzymes is proposed.

Glucose and sulfate conjugations of phenol, β-naphthol and 3-hydroxybenzo[a]pyrene by the American lobster ( Homarus americanus)

Little is known of the potential for conjugation of phenolic compounds by lobsters. Studies were designed to determine the ability of American lobster tissues to conjugate the phenolic compounds phenol, β-naphthol and 3-hydroxybenzo[a]pyrene (3-OH BaP). Aryl sulfotransferase (ST) activity was present in the cytosolic fraction of the antennal gland (AG), but not hepatopancreas (HP), whereas UDP-glucosyltransferase (UDPGT) activity was found in musomal fractions of both AG and HP. We observed differences between male and female lobsters in their ability to conjugate phenols. For example, in males the apparent K m for PAPS of AG β-naphthol ST was 9.0 ± 4.2 μM (mean ± SD, n = 5) and V max was 77 ± 7 pmol/min/mg protein, whereas in females K m was 62 ± 3 μM ( n = 3) and V max was 254 ± 92 pmol/min/mg protein ( P < 0.05). The β-naphthol UDPGT exhibited different pH optima in HP (10.5) and AG (7.5) musomes, suggesting that more than one form of β-naphthol UDPGT exists in the American lobster. With few exceptions, K m values for the phenolic substrates were in the μM range for both UDPGT and ST, whereas K m values for the cosubstrates were lower for PAPS than for UDP-glucose.

UDP-glucosyltransferase activity toward exogenous substrates in Drosophila melanogaster

To investigate the capacity of Drosophila extracts to glucosylate exogenous substrates we have developed a fast and sensitive method for the detection of UDP-glucosyltransferase activity using 4-nitrophenol, 1-naphthol, or 2-naphthol as substrates. High-performance liquid chromatography was used to separate and quantitate the reaction products, allowing detection of activities that produced as little as 1 pmol of 2-naphthol glucoside (fluorescence detection) or 16 pmol of 4-nitrophenol glucoside (absorbance detection). Optimal activity was found at 43°C and alkaline pH. The affinity of the Drosophila enzyme was 250-fold higher for 1-naphthol or 2-naphthol ( K m ≈ 4 μm) than for 4-nitrophenol and UDP-glucose ( K m ≈ 1 mm).

Biosynthesis of xanthurenic acid 8-O-beta-D-glucoside in Drosophila. Characterization of the xanthurenic acid:UDP-glucosyltransferase activity.

Xanthurenic acid 8-glucoside is a side metabolite of the tryptophan-xanthommatin pathway in Drosophila. From 3-hydroxykynurenine, two biosynthetic pathways can be envisaged, one via xanthurenic acid, and another via 3-O-glucoside of 3-hydroxykynurenine. In this report evidence is presented to show that the synthesis takes place via xanthurenic acid. (a) We have demonstrated that the Drosophila melanogaster vermilion purple mutant (unable to synthesize 3-hydroxykynurenine) synthesizes xanthurenic acid 8-glucoside when fed with xanthurenic acid; and (b) the activities required for its synthesis via xanthurenic acid have been found (3-hydroxykynurenine transaminase and xanthurenic acid:UDP-glucosyltransferase). This is the first time that a UDP-glucosyltransferase activity that utilizes xanthurenic acid has been demonstrated. The enzyme in crude extracts from Drosophila sordidula shows the following characteristics. (a) It has optimal activity at 35 degrees C at pH 7.1 (in buffer Tris-HCl), and in the presence of a divalent cation (Mg2+ or Mn2+); (b) the activity is inhibited by xanthurenic acid (above 1.5 mM), UDP, D-gluconic acid 1,5-lactone, and Triton X-100; (c) it is localized in both the microsomal and the soluble fractions; (d) the specific activity is two times higher in heads than in bodies; and (e) the activity is enhanced in flies fed with phenobarbital.

Biosynthesis of naringin in Citrus paradisi: UDP-glucosyl-transferase activity in grapefruit seedlings

A UDP-glucosyltransferase activity capable of position-specific transfer of glucose to the 7-position of naringenin has been isolated from grapefruit seedlings. Leaves are the richest source of this activity on a fresh weight basis. Characteristics include a pH optimum of 6.5–7.5, a temperature optimum of 37°, an apparent E act of 7.76 kcal mol −1, and an apparent K m for naringenin of 0.08 mM. Hesperitin and 2′,4′,6′,4-tetrahydroxychalcone are also glucosylated with apparent K m 's of 0.11 mM and 0.13 mM respectively. Thermal degradation studies indicate that the naringenin and hesperitin glucosylating activities have different stabilities. Chromatofocusing resolves the naringenin glucosylating activity into two peaks with apparent pI's of 4.4 and 3.9. The hesperitin glucosylating activity separates into three peaks with apparent pI's of 4.5, 4.4, and 4.0.

Cytochrome P-450 and Phase II activities in the gumboot chiton Cryptochiton stelleri

The digestive gland of Cryptochiton stelleri was shown to contain cytochrome P-450, benzo[ a]pyrene hydroxylase (BPH), and NAPHH-cytochrome P-450 reductase. Glutathione- S-transferase, UDP-glucuronosyltransferase, and UDP-glucosyltransferase activities also were observed. After treating chitons three weeks with a cytochrome P-450 inducer, β-naphthoflavone (BNF), a significant ( P < 0.05) increase in BPH was found in treated animals. The major metabolites extracted after incubation of BP with chiton digestive gland microsomes were quinones. However, a quantitative difference in quinone production was seen between controls (72.7%) and BNF-treated animals (42.9%). Neither ethoxycoumarin- O-deethylase (ECOD) or ethoxyresorufin- O-deethylase (EROD) was detected in controls or BNF-treated animals.