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Monooxygenase Activity (monooxygenase + activity)
Selected AbstractsCross-resistance study and biochemical mechanisms of thiamethoxam resistance in B-biotype Bemisia tabaci (Hemiptera: Aleyrodidae)PEST MANAGEMENT SCIENCE (FORMERLY: PESTICIDE SCIENCE), Issue 3 2010Yuntao Feng Abstract BACKGROUND: B-biotype Bemisia tabaci (Gennadius) has invaded China over the past two decades. To understand the risks and to determine possible mechanisms of resistance to thiamethoxam in B. tabaci, a resistant strain was selected in the laboratory. Cross-resistance and the biochemical mechanisms of thiamethoxam resistance were investigated in the present study. RESULTS: A 66.3-fold thiamethoxam-resistant B. tabaci strain (TH-R) was established after selection for 36 generations. Compared with the susceptible strain (TH-S), the selected TH-R strain showed obvious cross-resistance to imidacloprid (47.3-fold), acetamiprid (35.8-fold), nitenpyram (9.99-fold), abamectin (5.33-fold) and carbosulfan (4.43-fold). No cross-resistance to fipronil, chlorpyrifos or deltamethrin was seen. Piperonyl butoxide (PBO) and triphenyl phosphate (TPP) exhibited significant synergism on thiamethoxam effects in the TH-R strain (3.14- and 2.37-fold respectively). However, diethyl maleate (DEM) did not act synergistically with thiamethoxam. Biochemical assays showed that cytochrome P450 monooxygenase activities increased 1.21- and 1.68-fold respectively, and carboxylesterase activity increased 2.96-fold in the TH-R strain. However, no difference was observed for glutathione S -transferase between the two strains. CONCLUSION: B-biotype B. tabaci develops resistance to thiamethoxam. Cytochrome P450 monooxygenase and carboxylesterase appear to be responsible for the resistance. Reasonable resistance management that avoids the use of cross-resistance insecticides may delay the development of resistance to thiamethoxam in this species. Copyright © 2009 Society of Chemical Industry [source] RNA-Interference Approach to Study Functions of NADPH,:,Cytochrome P450 Oxidoreductase in Human HepatocytesCHEMISTRY & BIODIVERSITY, Issue 11 2009Diana Abstract Human NADPH,:,cytochrome P450 oxidoreductase (POR) is encoded by a single gene on chromosome 7q11.2. This flavoprotein donates electrons derived from NADPH to a variety of acceptor proteins, including squalene monooxygenase, heme oxygenase, cytochrome b5, and many microsomal cytochromes P450 (CYPs), which are involved in oxidative drug metabolism, steroidogenesis, and other functions. Numerous aspects related to cellular POR expression have not been systematically investigated. Interestingly, POR expression is lower compared to CYPs and may thus be limiting for monooxygenase activities, but conversely, POR knock-out in mice resulted in compensatory upregulation of CYPs. POR may also influence intracellular cholesterol and lipid homeostasis. To systematically investigate such effects, we developed specific POR gene silencing in cell lines and primary human hepatocytes by RNA interference using small interfering RNAs (siRNAs). In HepG2 cells, POR mRNA could be reduced by 95% over 4 days accompanied by reduced protein content and activity. In primary human hepatocytes, POR mRNA knock-down was less effective and more variable. Analysis of CYPs indicated induction of CYP3A4 but not CYP1A2 or CYP2D6. These results demonstrate that POR can be efficiently and almost completely silenced in HepG2 cells and, at least partially, in primary human hepatocytes. This will allow systematic studies of various consequences of POR variability in human cells. [source] Polycyclic aromatic hydrocarbons, aliphatic hydrocarbons, trace elements, and monooxygenase activity in birds nesting on the North Platte River, Casper, Wyoming, USAENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 3 2001Thomas W. Custer Abstract Tree swallow (Tachycineta bicolor) and house wren (Troglodytes aedon) eggs and chicks were collected near a refinery site on the North Platte River, Casper, Wyoming, USA and at a reference site 10 km upstream. Total polycyclic aromatic hydrocarbon (PAH) concentrations in swallow and wren chicks were higher at the refinery site than at the reference site. Polycyclic aromatic hydrocarbon concentrations in sediment and chick dietary samples were consistent with these findings. The general lack of methylated PAHs in sediment, diet, and bird carcasses suggested that the PAHs were derived from combustion and not from petroleum. The predominance of odd-numbered aliphatic hydrocarbons and the low ratios (,0.25) of pristane:n -C17 and phytane:n -C18 in chick and diet samples also suggested that swallow and wren chicks were not being chronically exposed to petroleum. Mean ethoxyresorufin- O -dealkylase and benzyloxyresorufin- O -dealkylase activities in tree swallow livers averaged nine times higher at the refinery site than at the reference site and were probably induced by exposure to PAHs. Trace element concentrations in eggs and livers of swallows and wrens were similar or greater at the reference site than at the refinery site. Selenium, strontium, and boron concentrations were elevated in eggs and livers of swallows and wrens at both the refinery and reference sites. [source] Fipronil resistance in the whitebacked planthopper (Sogatella furcifera): possible resistance mechanisms and cross-resistancePEST MANAGEMENT SCIENCE (FORMERLY: PESTICIDE SCIENCE), Issue 2 2010Jian Tang Abstract BACKGROUND: The whitebacked planthopper (WBPH), Sogatella furcifera (Horváth), is a major rice pest in many parts of Asia. Fipronil has been widely used to control rice pests, and resistance to fipronil has been reported in some important species. RESULTS: A field population (F) of WBPH was collected, with 50.5-fold resistance to fipronil, which increased to 137.5-fold (F-se) after continuous selection for 11 generations. The F-se population did not show significant cross-resistance to the insecticides examined by comparison with the F population. TPP (synergism ratio 1.9), DEM (1.5) and PBO (1.1) showed only slight synergism on fipronil in the F-se population. A large increase was found in esterase and P450 monooxygenase activity in the F-se population. In vitro, PBO inhibited both esterase and P450 monooxygenase activity, and TPP inhibited esterase activity in the F-se population. CONCLUSION: Synergistic study in vivo and biochemical study in vitro indicated that esterase and P450 monooxygenases might be important factors for fipronil resistance in the selected population F-se. However, these biochemical factors could not lead to such high resistance (137.5-fold) in the F-se population, and target-site insensitivity would be another or more important factor. Copyright © 2009 Society of Chemical Industry [source] Comparative Biochemistry of Eumelanogenesis and the Protective Roles of Phenoloxidase and Melanin in InsectsPIGMENT CELL & MELANOMA RESEARCH, Issue 1 2002Manickam Sugumaran The phenolic biopolymer eumelanin is an important skin pigment found throughout the animal kingdom. The enzyme, tyrosinase, initiates melanogenesis in mammals. The biogenesis is assisted by a number of mammalian protein factors including dopachrome tautomerase and 5,6-dihydroxyindole-2-carboxylate oxidase. Invertebrates, such as insects, employ phenoloxidase and dopachrome (decarboxylating) isomerase for melanin biosynthesis. Recently generated molecular biological and biochemical data indicate that tyrosinase and phenoloxidase are distinctly different enzymes in spite of possessing both monophenol monooxygenase activity as well as o -diphenoloxidase activity. Similarly, insect dopachrome isomerase also differs significantly from its mammalian counterpart in several of its properties including the nature of the enzymatic reaction. In addition, there are considerable differences in the eumelanogenic pathways of these two animal groups that include the utility of substrates, use of dihydroxyindoles and the nature of eumelanin pigment. Thus, the biochemistry and molecular biology of melanogenesis in mammals and insects are significantly different. The advantages of generating different eumelanin pigments and intermediates by the insects are discussed. [source] | |||||||||||||