Polysubstrate Monooxygenase Activities Research Articles

Laboratory colonization has not reduced constitutive or induced polysubstrate monooxygenase activity in velvetbean caterpillars

We evaluated whether velvetbean caterpillars (Anticarsia gemmatalis) from a laboratory colony had reduced constitutive (basal) and/or induced activities of their polysubstrate monooxygenase (PSMO) detoxification enzyme system as a result of long-term rearing (> 100 generations) on artificial diet without introduction of field-collected individuals. Larvae from the laboratory colony and those from a recently collected field strain were fed either a standard artificial diet (control), one containing the inducing allelochemical, flavone, or foliage ofIndigofera hirsuta (a host plant of this species), and their midgut PSMO activity was assessed by measuring the in vitro rate of aldrin epoxidation. Compared with the field-strain larvae, caterpillars from the laboratory colony had 1.9-fold greater constitutive activity (standard artificial diet) and 2.3-fold greater induced activity (flavone-treated diet). In addition, the magnitude of induction was somewhat greater for the laboratory-colony larvae (induced activity was 2.0-fold greater than constitutive activity) compared with those from the field-strain (1.6-fold). In contrast, no difference in strain activity was found when larvae were fedI. hirsuta foliage. The lower PSMO activity of the field-strain larvae when fed artificial diet may have been caused by their reduced feeding and growth performance compared with laboratory-colony larvae, and it may explain their greater sensitivity to allelochemicals incorporated in the artificial diet, as we found previously. The results of this study indicate that long-term rearing of theA. gemmatalis laboratory colony on artificial diet, without the introduction of field individuals, apparently has not selected for low constitutive activity or decreased inducibility of PSMO, and thus these larvae provide a suitable model for studying xenobiotic detoxication. In addition, they suggest that using an artificial diet to evaluate resistance to pesticides or other xenobiotics in fieldcollected insects, as is frequently done, may underestimate the level of resistance if the diet, through various causes, reduces the activity of detoxification enzymes contributing to the resistance.

Biotransformation activities of feral fish in waters receiving bleached pulp mill effluents

AbstractPerch (Perca fluviatilis L.), roach (Rutilus rutilus L.) and bream (Abramis brama L.) were collected from an area in the southern part of Lake Saimaa (Finland), which is polluted by effluents from the pulp and paper industry, and compared to fish caught at several upstream locations in the same lake system. Livers were sampled in the field, and polysubstrate monooxygenase (PSMO) activities and other parameters of the microsomal cytochrome P‐450 system, as well as conjugation enzymes, were later analyzed in the laboratory. The enzymes assayed included 7‐ethoxyresorufin O‐deethylase, pentoxyresorufin O‐dealkylase, benzo[a]pyrene hydroxylase, UDP‐glucuronosyltrans‐ferase and glutathione S‐transferase. The influence of effluents discharged from the mill, which produces chlorine‐bleached kraft pulp, was seen in each fish species as elevations of liver PSMO activities. The content of total glutathione was increased in fish collected from the most polluted areas, but the changes in conjugation enzymes were not as clearly related to the pollution gradient. These results were compared to analyses from several control areas located at various distances upstream from the industry investigated. To assess the possible influence of another pulp mill, Baikalsk Cellulose Combine, hepatic PSMO activities of Cottus kessleri and Paracottus kneri, two sculpins endemic to Lake Baikal (USSR), were also measured. In this case no effects were observed. In conclusion PSMO enzymes analyzed from stationary feral fish can serve as a tool for assessing and monitoring chemical contamination caused by pulp and paper mill effluents.

Effects of protein and juglone on gypsy moths: Growth performance and detoxification enzyme activity

The individual and interactive effects of dietary protein and juglone on larval performance and midgut detoxification enxymes were investigated for the gypsy moth,Lymantria dispar. The experimental design was a 2 × 3 factorial, with two levels of protein and three levels of juglone. We monitored survival/development rates from egg hatch to pupation and conducted fourth-instar feeding trials for determination of nutritional indices. Enzyme solutions were prepared from midguts of fifth instars and assayed for polysubstrate monooxygenase, esterase, quinone reductase, and glutathione transferase activities. Results showed that low protein levels prolonged development times, increased consumption rates, and reduced pupal weights. Juglone markedly reduced survival, growth, and consumption rates, increased development times, and reduced pupal weights. The interaction between protein and juglone influenced larval digestion efficiencies and female pupal weights. Polysubstrate monooxygenase activities were unaffected by diet, whereas esterase activities increased in response to both low dietary protein and presence of juglone. Low protein levels increased soluble quinone reductase activities but decreased glutathione transferase activities. Glutathione transferase activities were lowest in larvae fed low-protein, high-juglone diets and may have contributed to the especially poor performance of larvae on those diets. Quinone reductase and glutathione transferase are the systems of importance in detoxification of juglone, and moderate to low activities of these enzymes may explain why gypsy moths perform poorly on members of the Juglandaceae.

Effects of immunosuppressive chemicals on lymphoid development in foetal thymus organ cultures.

A murine foetal thymus organ culture system was employed to screen a number of immunotoxic chemicals for direct thymus toxicity. The toxic effects caused by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and its congeners on the system used had previously been shown to be similar to those caused in vivo on lymphoid development. The most potent compound tested was the corticosteroid fluocinolone acetonide, which caused a 50% inhibition of lymphoid development (EC50) at a concentration of 5 x 10(-11) M. The EC50 of TCDD was around 5 x 10(-10) M while that of 4 beta-phorbol 12-myristate 13-acetate (TPA) was ca 10(-7) M. TCDD and its congeners are believed to act via binding to the Ah receptor. Other known or presumed ligands of this receptor, which are potent inducers of P1-450 (P-448) -dependent polysubstrate monooxygenase activities, were considerably less toxic with EC50 levels varying between 10(-5) M (7,12-dimethylbenz(alpha-) antracene, alpha-naphthoflavone, benzo(alpha)pyrene) and 10(-4) M (beta-naphthoflavone and 3-methylcholantrene). Dinaphtho/2,3-b,5,6-b/dioxin and indolo/2,3-b/carbazole showed toxicity at 5 x 10(-6)-10(-5) M and 5 x 10(-5) M respectively. TCDD, TPA, and fluocinolone showed additive effects when added two by two in different combinations. Thus fluocinolone, known to counteract the toxicity and epidermal growth factor (EGF) cell-surface receptor-decreasing activity caused by TPA in other cell types, failed to decrease TPA toxicity in the thymus culture system.

Intercolony Variation in Pesticide Detoxification by the Honey Bee (Hymenoptera: Apidae)

Variation in polysubstrate monooxygenase activity, as measured by the epoxidation of aldrin, was studied in colonies of the honey bee, Apis mellifera L. Significant differences were found among colonies in spring, summer, and fall. In addition, colonies varied in their detoxification capacity from season to season, being least able to metabolize aldrin in the spring. Significant regression of the LD50 of diazinon on aldrin epoxidase activity indicated the involvement of these enzymes in determining intercolony diazinon resistance. The results also suggest that studying a number of populations with quantitatively different monooxygenase activities can give information on the in vivo metabolism of phosphorothioate insecticides.

Microsomal Polysubstrate Monooxygenase Activity in Western and Mountain Pine Beetles (Coleoptera: Seolytidae)

On the basis of polysubstrate monooxygenase (PSMO) activities in midgut tissue, we detected no difference in the biochemical breadth of diet of western pine beetles, Dendroctonus brevicomis Le Conte, and mountain pine beetles, D. ponderosae Hopkins. This result suggests that the number of taxa that these insects encounter may not be an accurate indicator of the diversity of toxins to which they are exposed. The biochemical diversity encountered by the host-restricted western pine beetle appears to be as great as that of the less host-restricted mountain pine beetle. PSMO activity of mountain pine beetles in their alternate host was significantly lower than that of mountain pine beetles in their preferred host; toxins in the alternate host may thus inhibit PSMO activity. Such inhibition may explain why, although mountain pine beetles colonize several different taxa throughout their geographic range, they prefer to colonize one taxon in any given locality and they shift to alternate hosts only rarely.

Polysubstrate monooxygenase activity and sex hormones in pre- and postspawning rainbow trout ( Salmo gairdneri)

The hepatic microsomal cytochrome P-450 content and polysubstrate monooxygenase (PSMO) activities as well as plasma levels of sex hormones in gonadally mature rainbow trout ( Salmo gairdneri) were studied. The plasma level of testosterone in prespawning female fish exceeded that of male fish. In both sexes, the testosterone level was at its highest in March and decreased considerably before the spawning time. The 17 β-estradiol content in female fish showed similar changes. The hepatic cytochrome P-450 content was at its lowest in prespawning fish in March, and significantly lower in females than in males. The sex difference in the cytochrome P-450 content disappeared after spawning. The absorption maximum of the reduced cytochrome-CO-complex varied from 449–450 nm without any correlation to the sex of the fish or the cytochrome P-450 content. In PSMO activities (benzo[ a]pyrene, 7-ethoxycoumarin, aminopyrine and ethylmorphine as substrates), a significant sex difference could be observed during the prespawning period. In all cases the activity was lower in females than in males. The 7-ethoxy-resorufin deethylase activity did not, however, show any sex difference. Benzo[ a]pyrene hydroxylase and 7-ethoxyresorufin deethylase activities in both sexes increased gradually during the pre- and postspawning times, being at their highest level in June. However, aminopyrine demethylase activity increased considerably during the prespawning period, and then decreased during and after spawning. The results indicate that changes in monooxygenase activities are dependent on the substrate used and the state of spawning, refering to the presence of multiple forms of cytochrome P-450 in the rainbow trout liver. Prior to spawning the rainbow trout is probably most sensitive to direct acting chemicals and most resistant to activation requiring compounds due to the much lowered levels of cytochrome P-450 and several monooxygenase activities.

Comparison of the inducibilities of UDP-glucuronosyltransferase and polysubstrate monooxygenase activities in mice exposed to 20 model xenobiotics

Comparison of the inducibilities of UDP-glucuronosyltransferase and polysubstrate monooxygenase activities in mice exposed to 20 model xenobiotics

Hepatic polysubstrate monooxygenase activities in different strains of rats fed cabbage (Brassica oleracea).

Weanling male Fischer (F), Long-Evans (LE), and Sprague-Dawley (SD) rats were fed a semi-purified basal diet or a 20% cabbage diet for 3 and 4 weeks. Hepatic polysubstrate monooxygenase (PSM) activity was measured. Significant strain differences were found in aniline hydroxylase and p-nitrophenol O-demethylase activities. Aniline hydroxylase and NADPH cytochrome c reductase activities were significantly decreased in all strains after 4 weeks of cabbage dietary treatment. F and LE rats consuming the cabbage diets also had significantly reduced O-demethylase activity after 4 weeks. Except in LE, aminopyrine N-demethylase activity tended to be elevated in the strains consuming the cabbage diets. Cabbage diets increased testes weight in SD and thyroid weights in LE rats. All strains showed decreased thymus weights in the cabbage dietary treatments. This study with rats shows that hepatic PSM activities, as well as some organ changes due to dietary cabbage are strain dependent.

Induction of polysubstrate monooxygenase and aflatoxin production by phenobarbitone in Aspergillus parasiticus NRRL 3240

The presence of the components of polysubstrate monooxygenase (PSMO) activity, viz., cytochrome P-450 and NADPH cytochrome P-450 reductase has been established for the first time in the microsomes of Aspergillus parasiticus . The microsomes were able to metabolize benzphetamine. NADPH cytochrome P-450 reductase, benzphetamine metabolism and aflatoxin production was increased by the presence of phenobarbitone (PB, 2mg/ml) in the medium. These results demonstrate that induction of PSMO activity could be a prerequisite for increased production of aflatoxins, since hydroxylation of intermediates is an obligatory step in aflatoxin biosynthesis.