The metabolism of R-20458 [(E)-6,7-epoxy-1-(4-ethylphenoxy)-3,7-dimethyl-2-octene] in rat hepatocyte suspensions

The metabolism of R-20458 [(E)-6,7-epoxy-1-(4-ethylphenoxy)-3,7-dimethyl-2-octene] by rat hepatocytes has been analyzed and compared with that of juvenile hormone I [methyl-(E,E)-cis-10,11-epoxy-7-ethyl-3,11-dimethyl-2,6-tridecadienoate] under identical conditions. The metabolism of R-20458 is characterized by the predominance of NADPH-dependent cytochrome P-450 and epoxide hydrolase reactions; whereas, JH I is metabolized mainly by carboxylesterase, epoxide hydrolase, and glutathione S-transferases. The metabolites of R-20458 have been shown to correspond to (E)-6,7-epoxy-1-(4-hydroxyethylphenoxy)-3,7-dimethyl-2-octene; (E)-6,7-epoxy-1-(4-acetylphenoxy)-3,7-dimethyl-2-octene; (E)-6,7-dihydroxy-1-(4-ethylphenoxy)-3,7-dimethyl-2-octene; and, (E)-6,7-dihydroxy-1-(4-acetylphenoxy)-3,7-dimethyl-2-octene. The production of the α-hydroxyethyl, p-acetylphenoxy, and acetylphenoxy-6,7-diol metabolites is markedly inhibited by SKF 525-A. No dramatic effects are produced by diethylmaleate and 1,2-epoxy-3,3,3-trichloropropane.     

Studies on a fluorescent insect growth regulator metabolite complex with house-fly microsomal cytochrome P-450

The fluorescent insect growth regulator 5[[[5-(dimethylamino)-1-naphthalenyl]amino]-1,3-benzodioxole (DNSAB) forms a metabolite complex with house-fly microsomal cytochrome P-450. Formation of the metabolite complex is dependent on the presence of NADPH and O₂; NADH supports the reaction at a reduced rate. The presence of antibodies to house-fly cytochrome c (P-450) reductase in reaction mixtures inhibits the complex formation, indicating that the reductase is necessary for transfer of electrons from NADPH to cytochrome P-450 to complete the reaction. In the oxidized form, the metabolite complex has a single absorbance maximum at 431 nm, whereas the reduced form has two absorbance maxima at 426 (major) and 455 nm (minor). The pH of the media affects the extinction of the 426- and 455-nm Soret bands; increased pH decreases the extinction of the 426-nm band and increases the extinction of 455-nm band. Formation of the DNSAB metabolite-cytochrome P-450 complex decreases the amount of CO-reactive cytochrome P-450 by 24%. The metabolite complex is not dissociable by treatment with ferricyanide or by using centrifugation techniques. Dissociation is accomplished by addition of DNSAB to the oxidized metabolite complex. Kinetic analysis of the complex formation gives apparent K_m and V_max values at 2.55 ± 1.0 μM and 1.1 ± 0.4 × 10^?2 ΔA min^?1 nmol^?1 cytochrome P-450, respectively. Addition of juvenile hormone [(E,E)-cis-methyl-10,11-epoxy-7-ethyl-3,11-dimethyl-2,6-tridecadienoate; JH] to the reaction medium competitively inhibits the formation of the metabolite complex giving an inhibition constant of 16 μM. DNSAB synergized the lethal effects of JH against Aedes aegypti larvae threefold; however, JH did not synergize DNSAB. These data suggest that DNSAB may acquire its hormonal qualities by complexing a species of cytochrome P-450 that metabolizes JH, thereby prolonging the in vivo lifetime of this hormone.     

Cytochrome P-450 in insects. 6. Age dependency and phenobarbital induction of cytochrome P-450, P-450 reductase,and monooxygenase activities in susceptible and resistant strains of Musca domestica

Development and phenobarbital (PB) induction of microsomal cytochrome P-450, cytochrome P-450 reductase, two epoxidation, and two O-demethylation activities were examined in chronologically timed populations of insecticide-susceptible (NAIDM) and -resistant (Rutgers) house flies. Measurements of these enzymes started with the pharate adult stage and ended 5 days following eclosion. Untreated insects of both strains had comparable reductase levels, whereas cytochrome P-450 and associated monooxygenase activities were 1.5-fold or more higher in Rutgers. Maximum induction, as well as toxicity, occurred at a lower PB concentration in NAIDM than Rutgers. The drug caused consistently higher increases in enzymes and activities within 12 hr of starting treatment in both strains. When PB was withdrawn from treated flies (both strains) 48 hr after treatment began, specific activities (product min^?1 mg protein^?1) in all enzymes returned to control values in 24 hr while metabolic capacity (product min^?1 insect^?1) achieved control values within 48 hr. The changes in turnover numbers (pmol product min^?1 pmol P-450^?1), in conjunction with the differences in the monooxygenation of the four substrates, suggest that PB treatment induced both a quantitative and qualitative change in NAIDM monooxygenation but only a quantitative change in Rutgers monooxygenation.     

Prochloraz,a potent inducer of the microsomal cytochrome P-450 system

Prochloraz (N-propyl-N-[2-(2,4,6-trichlorophenoxy)ethyl]-imidazole-1-carboxamide), a recently developed agricultural fungicide, is a potent inducer of microsomal enzymes. Rats fed 7 days with a prochloraz-contaminated diet (2500 ppm) showed an increase in hepatic cytochrome P-450, cytochrome b₅, and microsomal protein level; aniline hydroxylase, 7-ethoxycoumarin dealkylase, 7-ethoxyresorufin dealkylase, NADPH-cytochrome c reductase, and epoxide hydrolase were significantly induced. At a lower dose (100 ppm), only an increase in cytochrome P-450 and 7-ethoxyresorufin dealkylase was noticed. As shown with aniline hydroxylase and 7-ethoxycoumarin dealkylase, prochloraz is also a potent inhibitor of drug-metabolizing enzymes. The interaction of prochloraz with hepatic microsomal fraction from rat liver was also studied. Prochloraz binds to oxidized cytochrome P-450 to produce a type II spectral change; the compound also binds to reduced cytochrome P-450. The binding of some ligands (7-ethoxycoumarin, n-octylamine, aniline, and imidazole) to oxidized cytochrome P-450 was determined after induction by prochloraz. Japanese quails (Coturnix coturnix) fed 7 days with a prochloraz-contaminated diet (2000 ppm) showed a dramatic increase in liver weight (2.5-fold) and both hepatic and duodenal cytochrome P-450 (9- and 12-fold, respectively).     

Insect juvenile hormones: Induction of detoxifying enzymes in the housefly and detoxication by housefly enzymes

The cecropia juvenile hormone and three of its analogs were compared as inducers of microsomal epoxidase, O-demethylase, and DDT dehydrochlorinase in the housefly, Musca domestica L. The compounds were the cecropia juvenile hormone, methoprene, hydroprene, 6,7-epoxy-3,7-diethyl-1-[3,4-(methylenedioxy)phenoxy]-2-octene, and piperonyl butoxide, a well known insecticide synergist. The compounds were administered by feeding at levels up to 1% in the diet for 3 days to 1-day-old female adults. Enzymes were then prepared and assayed for their activity using heptachlor, p-nitroanisole, and DDT as substrates.There was approximately a twofold increase in the microsomal oxidases and a 50% increase in DDT dehydrochlorinase after the treatment with the cecropia juvenile hormone, while methoprene had some activity as an inducer of the epoxidase (30% increase) but no activity in the case of the O-demethylase or the dehydrochlorinase. Hydroprene had no effect on any of the enzyme systems, while 6,7-epoxy-3,7-diethyl-1-[3,4-(methylenedioxy)phenoxy]-2-octene was an inhibitor of the two microsomal oxidases. The latter compound and piperonyl butoxide were strong inducers of DDT dehydrochlorinase, causing approximately twofold increases in the activity of this enzyme.There was evidence that the microsomal preparations were able to metabolize and inactivate methoprene and hydroprene, the action being oxidative in the case of methoprene and both oxidative and hydrolytic in the case of hydroprene. The oxidative metabolism of the two juvenile hormone analogs by the microsomal preparations was inducible by the cecropia juvenile hormone and by phenobarbital and dieldrin.     

Effects of some insect development inhibitors on mosquito larvae

The compounds tested were isopropyl (±)-(E,E)-11 -methoxy-3,7,11-trimethyl-dodeca-2,4-dienoate (ZR 515) and 6,7-epoxy-3-ethyl-7-methylnonyl 4-ethylphenyl ether (R 20458) (two juvenile hormone mimics); 2,6-di-tert-butyl-4-(αα-dimethyl-benzyl)phenol (MON 0585) (which inhibits melanisation during pupation); diflubenzuron and 1-(4-chlorophenyl)-3-(2,6-dichlorobenzoyl)urea (PH 60:38) (which affect chitinisation during moulting); and (E)-oct-2-enoic acid and (E)-non-2-enoic acid (all of which are claimed to have “teratogenic” effects on insects). The relative potencies of these chemicals were assessed on eggs, larvae and pupae of several mosquito species. Their characteristic delayed harmful effects are described and related to various stages of metamorphosis.     

Monooxygenases from soybean root nodules: Aldrin epoxidase and cinnamic acid 4-hydroxylase

The metabolism of aldrin and trans-cinnamic acid within the root nodules of soybean (Glycine max. cv. Forrest) was investigated. In vitro studies with microsomal preparations revealed the presence of two distinct monooxygenase enzymes requiring NADPH and molecular oxygen. This was shown by different distributions in membrane fractions from sucrose density gradients. In addition, cinnamic acid hydroxylase was sensitive to carbon monoxide (CO), similar to cytochrome P-450-dependent monooxygenases, whereas aldrin epoxidation was not. Cyanide ion, strongly inhibited the epoxidase, without affecting hydroxylase activity. The superoxide radical (O₂⁻) scavengers, superoxide dismutase and norepinephrine, inhibited aldrin epoxidation but allowed greater cinnamic acid 4-hydroxylase activity. These results indicate aldrin epoxidase, in contrast to cinnamic acid hydroxylase, does not involve cytochrome P-450, and may instead utilize a peroxidase-like hemoprotein.     

Polysubstrate monooxygenases (cytochrome P-450) in larvae of susceptible and resistant strains of house flies

The polysubstrate monooxygenases (PSMO or cytochrome P-450) of house fly larvae were studied at the mature larval or “clear gut” stage. Fat body and gut tissues were most efficient in the conversion of aldrin to dieldrin. Microsomal fractions of larval homogenates had the highest PSMO activities, with lower PSMO activities also found associated with mitochondrial fractions. Microsomes from Rutgers (resistant) larvae had higher levels of NADPH:cytochrome c reductase (2×), cytochrome P-450 (2×), aldrin (4×), and heptachlor (9×) epoxidases than microsomes from CSMA (susceptible) larvae. Cytochrome P-450 of Rutgers larvae had an absorption maximum at 449 nm, 2 nm lower than the cytochrome P-450 of CSMA larvae. n-Octylamine spectra showed that the level of high-spin cytochrome P-450 was higher in Rutgers larvae. NADPH:cytochrome c reductase, cytochrome P-450, and aldrin epoxidase were induced by phenobarbital, and Rutgers larvae were shown to be more sensitive to this inducer than CSMA larvae. Induction of larval PSMO by phenobarbital did not affect the expression or the inducibility of PSMO in adults.     

Comparative inhibition of the juvenile hormone esterases from Trichoplusia ni,Tenebrio molitor, and Musca domestica

Twenty-seven compounds were screened as potential inhibitors of juvenile hormone esterases. Of these compounds O-ethyl-S-phenyl phosphoramidothiolate provided the best inhibition for the cabbage looper, Trichoplusia ni (Hubner), and the yellow mealworm, Tenebrio molitor L., while the juvenile hormone esterases of the house fly, Musca domestica L., were best inhibited by a juvenoid carbamate (1-(m-phenoxy-N-ethyl carbamate)-3,7-dimethyl-7-methoxy-2E-octene). The inhibition patterns of T. ni and T. molitor are similar, while those of M. domestica are relatively different. Further studies on the juvenile hormone and α-napthyl acetate esterases of T. ni showed that they could be differentially inhibited. Diisopropyl phosphorofluoridate and an alkyl trifluoromethyl ketone selectively inhibit the hydrolysis of α-naphthyl acetate and juvenile hormone, respectively, while O-ethyl-S-phenyl phosporamidothiolate inhibits both enzymes. The juvenile hormone esterases of T. ni also appear to be unique enzymes that are selective for juvenile-hormone-like molecules. The in vivo inhibition of T. ni juvenile hormone esterases by O-ethyl-S-phenyl phosphoramidothiolate slows the in vivo hydrolysis of juvenile hormone and results in delayed pupation and malformed larvae that resemble larval-pupal intermediates. Thus, the esterases involved in juvenile hormone metabolism appear to be important in juvenile hormone regulation.     

Alterations in microsomal cytochrome P-450-catalyzed reactions as a function of chlordecone (Kepone) induction

The effects of chlordecone treatment on the hepatic microsomal monooxygenase system of male rats were investigated. Chlordecone increased the microsomal content of cytochrome P-450, NADPH-cytochrome P-450 (c) reductase and, to a lesser extent, cytochrome b₅ in a time- and dose-dependent manner. The content of NADH-cytochrome b₅ (c) reductase was reduced. The turnover of seven substrates was studied in detail and, with the exception of aniline, was found to be increased between 1.3- and 2.2-fold. The apparent K_m's for these substrates were increased 2.1- to 16.7-fold. In addition, zoxazolamine paralysis time was reduced as a result of chlordecone treatment. These kinetic changes are explained on the basis of alterations in the cytochrome P-450 pool together with residual chlordecone acting as an inhibitor of substrate turnover. The sodium dodecyl sulfate-polyacrylamide gel electrophoresis protein pattern of microsomes isolated from chlordecone-treated rats more closely resembled that of microsomes isolated from untreated rats than that of microsomes isolated following phenobarbital or 3-methylcholanthrene treatment.     

Cytochrome P-450 content and aldrin epoxidation to dieldrin in isolated rat hepatocytes

A rat hepatocyte suspension effectively epoxidized aldrin to dieldrin with a V_max of 7.19 mol/mol P-450/min and a K_m of 9.27 μM. Viability and metabolic activity were stable for 6 hr after isolation when cells were maintained at room temperature (20°C) with the gentle introduction of $\text{O}{}_2\text{CO}{}_2$ onto the surface of the suspension. The cytochrome P-450 content of the suspension was 303 pmol/10⁶ cells. Primary maintenance culture of the cells also epoxidized aldrin. During culture for 3 days, metabolic activity decreased slowly day by day. Metabolic activity of microsomal fraction from rat liver was also examined. Microsomes epoxidized aldrin with a V_max of 5.11 mol/mol P-450/min and a K_m of 1.64 μM. Significant loss of some subspecies of cytochrome P-450 during fractionation of liver homogenate was indicated.     

Hepatic microsomal oxidative metabolism of pesticides and other xenobiotics in pregnant CD1 mice

Pregnancy-related changes in oxidative metabolism of several xenobiotics including pesticides were examined in the hepatic microsomes of CD₁ mice. The effect of pregnancy on hepatic microsomal cytochrome P-450-catalyzed substrate oxidation was found to be dependent upon the type of reaction examined. Not all substrates undergoing the same reaction showed identical changes during pregnancy. Those enzyme activities which exhibited a decline in specific activity during pregnancy generally exhibited no change in total hepatic capacity. Enzymes posting no change in specific activity throughout gestation generally showed large increases in total hepatic activity. Phorate S-oxidation was catalyzed by both microsomal flavin-containing monooxygenase (MFMO) and cytochrome P-450. Moreover, there was no pregnancy-related change in either MFMO or total enzymatic (MFMO plus cytochrome P-450) phorate S-oxidation.     

Inhibition of epoxidation of methyl farnesoate to juvenile hormone III by cockroach corpus allatum homogenates

Radiolabeled methyl farnesoate is epoxidized to juvenile hormone III by an NADPH-dependent reaction occurring in corpus allatum homogenates from the cockroach Blaberus giganteus L. Most of the enzymatically produced juvenile hormone has the 10R configuration described for previously isolated natural juvenile hormones. The unnatural 2Z geometrical isomer of methyl farnesoate is epoxidized by the above system faster than the natural 2E isomer. Several series of chemicals known to be inhibitors of mixed-function oxidases were surveyed as inhibitors of methyl farnesoate epoxidation. The anti-juvenile hormone precocene II caused negligible inhibition at 1 · 10^?4M, whereas the best inhibitor was o-bromophenoxymethyl-imidazole with an apparent I₅₀ of 4 · 10^?7M. None of the inhibitors tested were potent morphogenetic agents on Tenebrio molitor pupae, and they failed to cause precocious development of Oncopeltus fasciatus nymphs. The inhibition of in vitro juvenile hormone biosynthesis suggests the possibility of finding an anti-hormone which acts by blocking juvenile hormone biosynthesis.     

Cytochrome P-450 in insects: 1. Differences in the forms present in insecticide resistant and susceptible house flies

Soluble cytochrome P-450 prepared from the microsomal fraction of abdomen homogenates of an insecticide resistant strain (Rutgers) and a susceptible strain (NAIDM) of the house fly, Musca domestica L., was characterized by spectral and electrophoretic methods. Six chromatographically distinct fractions were obtained after chromatography on DEAE-cellulose and hydroxylapatite. Examination of the six fractions by difference spectrophotometry indicated that the wave lengths for maximum absorption of the cytochrome P-450-carbon monoxide complexes were at 450, 451, and 452 nm for the NAIDM fractions and at 449, 450, and 451 nm for the Rutgers fractions. The type II binding spectra of the cytochrome P-450 in each fraction were measured with n-octylamine. Several of these resembled spectra which, in studies of hepatic cytochrome P-450, have been shown to be due to the presence of the high spin form of this hemoprotein. Four of the fractions from the resistant strain were of this type compared to one from the susceptible strain. Electrophoresis experiments indicated that there were at least three hemoproteins in the 40,000–60,000 molecular weight range in the fractions from the resistant strain while four could be detected in those from the susceptible strain. The specific aldrin epoxidase activity of the most active Rutgers fractions was considerably higher than that of similar fractions from the NAIDM microsomes in reconstitution experiments.     

Cytochrome P-based resistance mechanism and pyrethroid resistance in the field Anopheles albimanus resistance management trial

The relative rates of cytochrome P⁴⁵⁰ selection in southern Mexican Anopheles albimanus populations were investigated during a 3 years indoor residual house spraying intervention with a pyrethroid (PYR) or DDT, a mosaic of organophosphate (OP)-PYR, and the annual rotation of OP-PYR-carbamate (CARB). This insecticide resistance mechanism, initially evenly spread in the mosquito population, correlated with PYR resistance during the second treated year, when cytochrome P⁴⁵⁰ contents increased in most villages of the PYR, rotation and mosaic schemes. However, by the third year, mean cytochrome P⁴⁵⁰ contents declined to susceptible levels in mosquitoes of the rotation and one mosaic group but not in the PYR-treated villages. In DDT-treated villages, a continuous decrement of cytochrome P⁴⁵⁰ levels occurred since the first treatment year, and susceptible levels were observed at the end of the intervention. Most correlations of cytochrome P⁴⁵⁰ levels and PYR resistance were lost during the third year, indicating that another mechanism evolved in resistant mosquito populations.     

Bimodal effect of methylenedioxyphenyl compounds on detoxifying enzymes in the housefly

Thirteen methylenedioxyphenyl (MDP) compounds, including commercial insecticide synergists and juvenile hormone analogs, were compared in their effect on detoxifying enzymes in the housefly (Musca domestica). Flies were fed a diet containing 1% of the compounds for 3 days. Enzymes were then assayed in vitro for their activity using aldrin and DDT as substrates. Piperonyl butoxide (PB), sesamex, propyl isome, sulfoxide, safrole, isosafrole, 6,7-epoxy-3,7-diethyl-1-[3-4(methylenedioxy) phenoxy]-2-octene (MDP-JH I) and 6,7-epoxy-3-methyl-7-ethyl-1-[3,4-(methylenedioxy) phenoxy]-2-octene (MDP-JH II) all caused a bimodal effect, inhibiting microsomal epoxidase and inducing DDT-dehydrochlorinase in the resistant Isolan-B strain. Two of these, PB and MDP-JH I, gave similar results with the susceptible strain, stw;w⁵ and two resistant strains, Fc-B and Orlando-DDT. However, o-safrole, piperonylic acid, piperonal, 3,4-methylenedioxybenzyl acetate and methyl-(3,4-methylenedioxy) benzoate had little or no effect on the enzyme systems studied. The standard susceptible strain (WHO-SRS) responded to these compounds very differently. Among those tested, piperonyl butoxide, sesamex, safrole, and isosafrole were inducers of microsomal epoxidase, a 4-fold increase occurring after treatment with sesamex. Only MDP-JH II showed a marked inhibition of the epoxidase. These treatments did not effect DDT-dehydrochlorinase activity in this strain.The enhancement of DDT-dehydrochlorinase activity by the MDP compounds is associated with an increased rate of DDT dehydrochlorination in vivo. The stimulatory effect could be blocked by treatment with actinomycin D or cycloheximide.     

Juvenile hormone analogs: In vitro metabolism in relation to biological activity in blow flies and flesh flies

Six juvenile hormone analogs of the alkyl 3,7,11-trimethyl-2,4-dodecadienoate type were compared as substrates for esterases and oxidases prepared from homogenates of the flesh fly (Sarcophaga bullata) and blow fly (Phormia regina). The esterase system was able to hydrolyze all of the analogs except the isopropyl ester, known commercially as methoprene or ZR-515. This result was consistent with the biological activity of the analogs, methoprene being more effective in preventing pupal-adult ecdysis. The esterases were present in all life stages in both species with the adult (abdomens) containing the highest titers. According to their reaction with paraoxon, the enzymes are classified as C-type esterases. Microsomal oxidases prepared from adult abdomens metabolized all of the juvenile hormone analogs.     

Mode of action of naphthalic anhydride as a safener for the herbicide AC 263222 in maize

In hydroponic experiments, seed-dressing with the herbicide safener 1,8-naphthalic anhydride (NA), significantly enhanced the tolerance of maize, (Zea mays L., cv. Monarque) to the imidazolinone herbicide, AC 263222, (2-[4-isopropyl-4-methyl-5-oxo-2-imidazolin-2-yl]-5-methylnicotinic acid). Uptake, distribution and metabolism studies where [¹⁴C]AC 263222 was applied through the roots of hydroponically grown maize plants showed that NA treatment reduced the translocation of radiolabel from root to shoot tissue and accelerated the degradation of this herbicide to a hydroxylated metabolite. Reductions in the lipophilicity and, therefore, mobility of this compound following hydroxylation may account for NA-induced retention of radiolabel in the root system. Hydroxylation of AC 263222 suggested that NA may stimulate the activity of enzymes involved in oxidative herbicide metabolism, such as the cytochrome P₄₅₀ mono-oxygenases. In agreement with this theory, the cytochrome P₄₅₀ inhibitor, 1-aminobenzotriazole (ABT), synergized AC 263222 activity and inhibited its hyroxylation in vivo. NA seed-dressing enhanced the total cytochrome P₄₅₀ and b₅ content of microsomes prepared from etiolated maize shoots. Isolated microsomes catalyzed AC 263222 hydroxylation in vitro. This activity possessed the characteristics of a cytochrome P₄₅₀ mono-oxygenase, being NADPH-dependent and susceptible to inhibition by ABT. Activity was stimulated four-fold following NA seed treatment. Differential NA enhancement of AC 263222 hydroxylase and the cytochrome P₄₅₀-dependent cinnamic acid-4-hydroxylase (CA4H) activity, suggested that separate P₄₅₀ isozymes were responsible for each activity. These results indicate that the protective effects of NA result from enhancement of AC 263222 hydroxylation and concomitant reduction in herbicide translocation. This may be attributed to the stimulation of a microsomal cytochrome P₄₅₀ system. © 1998 SCI.     

Methylenedioxyphenyl complexes with microsomal cytochrome P-450: In vivo complex formation in rat liver and in midgut tissues of the Southern armyworm (Spodoptera eridania)

The capacity of several methylenedioxyphenyl insecticide synergists to generate metabolite complexes with cytochrome P-450 was studied in midgut tissues of the Southern armyworm (Spodoptera eridania). Examination of the NADH-reduced versus oxidized spectra from methylene-dioxyphenyl-induced midgut indicated that isosafrole, dihydrosafrole, and 4-ethoxy-1,2-methylenedioxybenzene generated metabolite complexes with a principal absorbance maximum at 427 nm and smaller absorbance maxima near 460 and 556 nm. Further studies with 2-n-heptylbenzimidazole showed that the complex between insect cytochrome P-450 and dihydrosafrole was unusually resistant to displacement. Initial rates of complex displacement in insect microsomes were found to be approximately an order of magnitude slower than those of the corresponding complexes in rat hepatic microsomes. Nevertheless, with the exception of the dihydrosafrole complex in insect microsomes, the “time to half-maximal displacement” parameter was found to be very similar for each complex. These findings indicate that the formation of dissociable complexes between cytochrome P-450 and the methylenedioxyphenyl metabolite occurs in both insect midgut and rat hepatic microsomes after in vivo exposure. From the present study it would appear that dihydrosafrole may constitute a useful probe to distinguish binding sites within insect and mammalian cytochrome P-450.     

Present Status of Research on Insect Growth Regulators for the Protection of Stored Grain1

Two insect growth regulators of the juvenile hormone type, namely 6,7-epoxy-3-ethyl-(p-ethylphenoxy)-7-methylnonane, cis/trans mixture (compound A) and 6,7-epoxy-3,7-dimethyl-1-[3,4-(methylendioxy)-phenoxy]-2-nonene (compound B) have been tested for their persistence when treated on stored grain. The interim results of this trial showed inhibition of adult emergence of Ephestia kühniella Zell., Plodia interpunctella Hübn., Tribolium castaneum Herbst and Rhyzopertha dominica F. even 8 months after treatment. The gas-chromatography residue determination of compound A showed a reduction of 27 % of the original concentration within 8 months. No effect of compound A on the endosperm of the grain or taste of flour and bread could be found in the Bakery School in Lucerne.