Squalene analogues containing isopropylidene mimics as potential inhibitors of pig liver squalene epoxidase and oxidosqualene cyclase

Several squalene analogues containing 1,1-dihaloalkene, acetylene, allene, diene, and cyclopropane functionalities were synthesized and evaluated as potential inhibitors of pig liver squalene epoxidase and oxidosqualene cyclase. Both monofunctionalized and bisfunctionalized analogues were prepared. Poor inhibition of squalene epoxidase and oxidosqualene cyclase was found for most compounds (IC50 much greater than 400 microM), with the exception of the monofunctionalized alkynol (IC50 = 300 microM). This alkynol showed mixed-function inhibition with KI = 0.95 mM. Oxidation of the alcohol to the alkynone resulted in loss of epoxidase activity, indicating that the hydroxyl group is necessary for inhibition and that the alkynol is not a proinhibitor. Molecular mechanics calculations indicated that a good inhibitor should possess hydrophobic substituents on an unpolarized, unsaturated system; additionally, the presence of a pro-C-3 hydroxyl group can confer inhibitory potency.

Expression of pheromone binding proteins during antennal development in the gypsy moth Lymantria dispar

We have identified 2 olfactory specific proteins in the gypsy moth Lymantria dispar that are uniquely associated with the male antennae, the principal olfactory organs of this animal. These proteins were the major soluble protein components of the olfactory sensilla, present in equivalent amounts. Both proteins comigrated on SDS-PAGE, showing an apparent molecular mass of 15,000 Da but migrated separately on non-SDS-PAGE, indicating differences in net charge. N-terminal amino acid sequence analysis showed that the 2 proteins share 50% identity, indicating that they are genetically distinct homologs. Both proteins bound the L. dispar sexpheromone, associated with antisera prepared against the previously identified phermone-binding protein (PBP) of the moth Antheraea polyphemus, and shared sequence identity with the A. polyphemus PBP. These 2 proteins are therefore identified as L. dispar PBPs and are termed PBP1 and PBP2 based on their migration differences on non-SDS-PAGE. It is estimated that PBP1 and PBP2 are present in the sensilla lumen at a combined concentration of 13.4 mM. The expression of the L. dispar PBPs was examined during the 11 d development of the adult antenna. PBP1 and PBP2 were first detected by non-SDS-PAGE analysis and Coomassie blue staining 3 d before adult eclosion, on day A-3. Levels increased, reaching a plateau on day A-1 that continued into adult life. In vivo labeling studies indicated that the rate of PBP synthesis increased from A-3 to a plateau on A-2, where it remained into adult life. In vitro translations of antennal mRNAs indicated that translatable PBP mRNA was available at a very low level on day A-4, increased slightly on A-3 and dramatically on A-2, and remained at a high level into adult life. PBP mRNA represented the major translatable mRNA in the antenna during this period. It was estimated that the PBPs undergo a combined steady-state turnover of 8 x 10(7) molecules/hr/sensillum. Cursory in vivo and in vitro translation studies of antennal mRNA from A. polyphemus and Manduca sexta showed similar temporal patterns of PBP expression, suggesting that the L. dispar observations are general.

Polyacrylamide gel miniaturization improves protein visualization and autoradiographic detection

Polyacrylamide gels shrink to one-quarter of their original area when soaked in a 50% (w/v) solution of polyethylene glycol. Gel miniaturization improves the contrast of protein bands, with four valuable consequences. (i) A 5- to 10-fold increase in sensitivity for Coomassie blue is observed. (ii) Gels are more durable; i.e., they resist tearing when wet and they do not crack during drying under vacuum. (iii) Shrunken gels give sharper photographic images and provide better interlane protein band comparisons. (iv) Condensed protein bands lead to an increased sensitivity for detecting low-abundance, radioactively-labeled proteins by fluorography.

Differential recognition of geometric isomers by the boll weevil,Anthonomus grandis Boh. (Coleoptera: Curculionidae): Evidence for only three essential components in aggregation pheromone

For two decades, the aggregation pheromone of the boll weevil,Anthonomus grandis Boh. (Coleoptera: Curculionidae), was thought to consist of four compounds: I [(+)-(Z)-2-isopropenyl-1-methylcyclobutane ethanol]; II [(Z)-3,3-dimethyl-Δ(I,β)-cyclohexane ethanol]; III [(Z)-3,3-dimethyl-Δ(1,α)-cyclohexane acetaldehyde); and IV [(E)-3,3-dimethyl-Δ(1,α)-cyclohexane acetaldehyde). Evidence is presented from behavioral and electrophysiological studies to show that only three of these components, I, II, and IV, are essential for attraction. Competitive field tests, in which each possible three-component blend was tested against the four-component mixture, demonstrated that omission of I, II. or IV resulted in decreased trap captures (P < 0.01). Trap captures by these blends lacking I, II, or IV resembled those by the hexane solvent alone in a similar experiment. However, omission of III did not significantly alter field attractiveness of the blend. Dosage-response curves constructed from electroantennogram responses of both males and females to serial dilutions of III, IV, and a 50∶50 mixture of the geometric isomers III and IV showed both sexes to be 10- to 100-fold more sensitive to IV than III. Data from the electrophysiological studies were consistent with a single acceptor type for the (E)-cyclohexylidene aldehyde, IV, for males, and possibly one or two acceptor types for III and IV for females. Possible roles for the (Z)-cyclohexylidene aldehyde, III, and implications for the pheromonal attractant currently used in boll weevil eradication/suppression programs are discussed.

Fluorography of tritium-labeled proteins in silver-stained polyacrylamide gels

Silver-staining of polyacrylamide gel electrophoresis (PAGE)-separated proteins allows sensitive detection of proteins but severely reduces the ability to detect weak beta-emitters present in the protein band. A simple procedure is described in which silver can be removed from a silver-stained PAGE gel (deargentation) using photographic fixer, and the silver-free gel can be enhanced and used for fluorography. A quantitative study of sensitivity is reported for 3H-labeled bovine serum albumin with a one-dimensional sodium dodecyl sulfate-PAGE slab gel.

Sex pheromone receptor proteins. Visualization using a radiolabeled photoaffinity analog

A tritium-labeled photoaffinity analog of a moth pheromone was used to covalently modify pheromone-selective binding proteins in the antennal sensillum lymph and sensory dendritic membranes of the male silk moth, Antheraea polyphemus. This analog, (E,Z)-6,11-[3H]hexadecadienyl diazoacetate, allowed visualization of a 15-kilodalton soluble protein and a 69-kilodalton membrane protein in fluorescence autoradiograms of electrophoretically separated antennal proteins. Covalent modification of these proteins was specifically reduced when incubation and UV irradiation were conducted in the presence of excess unlabeled pheromone, (E,Z)-6,11-hexadecadienyl acetate. These experiments constitute the first direct evidence for a membrane protein of a chemosensory neuron interacting in a specific fashion with a biologically relevant odorant.

Detection and microsequencing of juvenile hormone-binding proteins of an insect by the use of an iodinated juvenile hormone analog

An [125I]iodinated juvenile hormone (JH) analog can be used as a sensitive and highly selective probe for the visualization of high-affinity, (JH)-specific binding proteins from insect hemolymph samples. The proteins can be detected in their native form using a two-dimensional (isoelectric focusing then native gradipore gel) separation of the crude protein mixture containing the 125I-labeled iodinated JH analog. The proteins can be transferred to activated glass fiber paper by electroblotting, and the location of the bound gamma-emitter can be found by exposure of the dried gel or the electroblot to X-ray film. The radiolabeled protein spot can be excised from the Coomassie-stained glass fiber paper and subjected directly to gas-phase N-terminal amino acid sequencing. This non-destructive, non-denaturing technique may have wide applicability in identifying and sequencing ligand-specific binding proteins in complex mixtures.

Synthesis and binding affinity of an iodinated juvenile hormone

The synthesis of the first iodinated juvenile hormone (JH) in enantiomerically enriched form is reported. This chiral compound, 12-iodo-JH I, has an iodine atom replacing a methyl group of the natural insect juvenile hormone, JH I, which is important in regulating morphogenesis and reproduction in the Lepidoptera. The unlabeled compound shows approximately 10% of the relative binding affinity for the larval hemolymph JH binding protein (JHBP) of Manduca sexta, which specifically binds natural 3H-10R,11S-JH I (labeled at 58 Ci/mmol) with a KD of 8 X 10(-8) M. It is also approximately one-tenth as biologically active as JH I in the black Manduca and epidermal commitment assays. The 12-hydroxy and 12-oxo compounds are poor competitors and are also biologically inactive. The radioiodinated [125I]12-iodo-JH I can be prepared in low yield at greater than 2500 Ci/mmol by nucleophilic displacement using no-carrier-added 125I-labeled sodium iodide in acetone; however, synthesis using sodium iodide carrier to give the approximately 50 Ci/mmol radioiodinated ligand proceeds in higher radiochemical yield with fewer by-products and provides a radioligand which is more readily handled in binding assays. The KD of [125I]12-iodo-JH I was determined for hemolymph JHBP of three insects: M. sexta, 795 nM; Galleria mellonella, 47 nM; Locusta migratoria, 77 nM. The selectivity of 12-iodo-JH I for the 32-kDa JHBP of M. sexta was demonstrated by direct autoradiography of a native polyacrylamide gel electrophoresis gel of larval hemolymph incubated with the radioiodinated ligand. Thus, the in vitro and in vivo activity of 12-iodo-JH I indicate that it can serve as an important new gamma-emitting probe in the search for JH receptor proteins in target tissues.

Chemistry of pheromone and hormone metabolism in insects

Chemical evidence is needed in both insect endocrinology and sensory physiology to understand hormone and pheromone action at the molecular level. Radiolabeled pheromones and hormones have been synthesized and used to identify binding and catabolic proteins from insect tissues. Chemically modified analogs, including photoaffinity labels and enzyme inhibitors, are among the tools used to covalently modify the specific acceptor or catalytic sites. Such targeted agents can also provide leads for the design of growth and mating disruptants by allowing manipulation of the physiologically important interactions of the chemical signals with macromolecules.

Comparison of crude and affinity purified cytosolic epoxide hydrolases from hepatic tissue of control and clofibrate-fed mice

An affinity purification procedure was developed for the cytosolic epoxide hydrolase based upon the selective binding of the enzyme to immobilized methoxycitronellyl thiol. Several elution systems were examined, but the most successful system employed selective elution with a chalcone oxide. This affinity system allowed the purification of the cytosolic epoxide hydrolase activity from livers of both control and clofibrate-fed mice. A variety of biochemical techniques including pH dependence, substrate preference, kinetics, inhibition, amino acid analysis, peptide mapping, Western blotting, analytical isoelectric focusing, and gel permeation chromatography failed to distinguish between the enzymes purified from control and clofibrate-fed animals. The quantitative removal of the cytosolic epoxide hydrolase acting on trans-stilbene oxide from 100,000g supernatants, allowed analysis of remaining activities acting differentially on cis-stilbene oxide and benzo[a]pyrene 4,5-oxide. Such analysis indicated the existence of a novel epoxide hydrolase activity in the cytosol of mouse liver preparations.

Fucosterol epoxide lyase of insects: synthesis of labeled substrates and development of a partition assay

Fucosterol epoxide labeled with tritium in the C-29 methyl has been synthesized and employed in the development of a partition assay which allows the rapid determination of fucosterol epoxide lyase activity in vitro in homogenates of insect tissues. An independent synthesis of [24-14C]fucosterol epoxide provided a control substrate to evaluate nondealkylative transfer of labeled steroid to the aqueous layer during the enzyme assay. The diastereomeric 24R,28R- and 24S,28S-[29-3H]fucosterol epoxides were obtained via HPLC separation of their benzoate esters. Homogenates of the midgut tissue of larval tobacco hornworms (Manduca sexta) were examined at pH 5 to 9 in several buffer systems, and at temperatures of 7 to 67 degrees C in phosphate buffer. Optimal activity was found using pH 7.4, 76 mM phosphate buffer at 37 degrees C. The 24R,28R diastereomer of fucosterol epoxide was metabolized at a rate at least 100 times that of the 24S,28S isomer by this enzyme system.

Kinetic properties of a sex pheromone-degrading enzyme: the sensillar esterase of Antheraea polyphemus

Behavioral and electrophysiological evidence has suggested that sex pheromone is rapidly inactivated within the sensory hairs soon after initiation of the action-potential spike. We report the isolation and characterization of a sex-pheromone-degrading enzyme from the sensory hairs of the silkmoth Antheraea polyphemus. In the presence of this enzyme at physiological concentration, the pheromone [(6E,11Z)-hexadecadienyl acetate] has an estimated half-life of 15 msec. Our findings suggest a molecular model for pheromone reception in which a previously reported pheromone-binding protein acts as a pheromone carrier, and an enzyme acts as a rapid pheromone inactivator, maintaining a low stimulus noise level within the sensory hairs.

Inhibition of epoxide metabolism by alpha,beta-epoxyketones and isosteric analogs

Chalcone oxides and several isosteric compounds have been prepared to examine the importance of the alpha,beta-epoxyketone moiety in the inhibition of the hydrolysis of [3H]-trans-stilbene oxide to its meso-diol by mouse liver cytosolic epoxide hydrolase (cEH). Inhibition of microsomal EH and glutathione S-transferase were also examined. For cEH, replacement of the carbonyl by methylidene reduces inhibitor potency by a factor of 44, while replacement of the epoxide ring with a cyclopropyl ring reduces inhibition by a factor of 450. A 2'-hydroxyl also reduces cEH inhibition by 100 times. These observations are consistent with a model of the active site in which the carbonyl is hy-hydrogen-bonded to an acidic site presumed to be involved in initiating epoxide hydrolysis. The chalcone oxides thus bind tightly but are not readily turned over as substrates.

High specific activity enantiomerically enriched juvenile hormones: synthesis and binding assay

A stereoselective total synthesis of chiral juvenile hormone I is described that allows stoichiometric introduction of two tritium atoms in the final step. Both optical antipodes of the pivotal epoxy alcohol intermediate were prepared in 95% enantiomeric excess by the Sharpless epoxidation of a (Z)-allylic alcohol. Elaboration of the hydroxy-methyl group to a vinyl group followed by selective homogeneous tritiation affords optically active juvenile hormone I analogs at 58 Ci/mmol. Competitive binding of the labeled 10R, 11S and 10S,11R enantiomers with unlabeled enantiomers to the hemolymph binding protein of Manduca sexta larvae was determined by using a dextran-coated charcoal assay. The natural 10R,11S enantiomer has twice the relative binding affinity of the 10S,11R enantiomer. The availability of such high specific activity optically pure hormones will contribute substantially to the search for high-affinity receptors for juvenile hormones in the nuclei of cells. Moreover, the chiral 12-hydroxy-(10R,11S)-epoxy intermediate allows modification of juvenile hormone for solid-phase biochemical and radioimmunochemical work without altering either the biologically important carbomethoxy or epoxy recognition sites.

Cyclopropyl oxiranes: reversible inhibitors of cytosolic and microsomal epoxide hydrolases

A series of aryl- and alkyl-substituted cyclopropyl oxiranes were synthesized as potential suicide inhibitors of mouse liver epoxide hydrolase (EH). The inhibitory potency of each compound and its corresponding alkene precursor was determined with mouse liver EHs using [3H]-cis-stilbene oxide as substrate for microsomal EH (mEH) and for glutathione-S-transferase, and using [3H]-trans-stilbene oxide for cytosolic EH (cEH). The cyclopropyl oxiranes all showed low (26-60% at 5 X 10(-4) M) inhibition of glutathione transferase and moderate inhibition (I50 = 5 X 10(-4) to 6 X 10(-6) M) for cEH and mEH. cis-Phenylcyclopropyl oxirane had an I50 for mEH near that for a commonly used inhibitor, 1,1,1-trichloropropene oxide. Inhibition appeared competitive and reversible, and the cyclopropyl oxiranes appeared to function as alternate substrates. Absence of irreversible inhibition is evidence against a strongly electrophilic epoxide-opening mechanism involving a cyclopropyl carbinyl-homoallyl cation rearrangement. Instead, a concerted mechanism is favored, in which electrophilic opening and hydroxide attack occur in a concerted fashion.

Rapid purification of cytosolic epoxide hydrolase from normal and clofibrate-treated animals by affinity chromatography

Epoxide hydrolase from liver cytosol (cEH) of both normal and clofibrate-treated mice can be bioselectively adsorbed onto an affinity column prepared from epoxy-activated Sepharose and 7-methoxycitronellyl thiol. The free ligand is a modest inhibitor of cEH (I50, approximately equal to 3 X 10(-4) M) and lacks the epoxide function necessary for it to be turned over as a substrate. This study demonstrates that a methoxy group can be used to mimic an oxirane in a vertebrate system. Bioselective elution of cEH can be accomplished with several chalcone oxides, which are selective potent inhibitors (I50, 1-50 X 10(-7) M), and activity can be recovered by dialysis. This procedure thus enhances the purification by offering independent opportunities for selective binding and selective elution. Conservatively, a 40%-80% recovery of partially inhibited enzyme activity can be achieved in 4-48 hr with a 30- to 90-fold purification. The purified cEH from clofibrate-induced animals was essentially homogeneous by NaDodSO4/PAGE and had an apparent subunit molecular weight of 58,000. The cEHs from normal and clofibrate-induced animals appeared identical by NaDodSO4/PAGE. Since the cEH activity in normal and clofibrate-treated animals is due to the same enzyme, the increase in cEH activity caused by selected hypolipidemic agents appears to be true induction.

Photoaffinity labeling of the hemolymph juvenile hormone binding protein of Manduca sexta

A synthetic analogue of the insect juvenile hormone (JH) III, 10,11-epoxy[10-3H]farnesyl diazoacetate [( 3H]-EFDA), binds to several proteins in a partially purified preparation of hemolymph protein from fourth instar larvae of Manduca sexta when irradiated with UV light. Approximately 80% of this binding could be inhibited by the addition of excess unlabeled JH I. To compare the relative affinity of EFDA for the juvenile hormone binding protein (JHBP) with that of the various JH homologues, the ability of unlabeled EFDA and JH homologues to displace [3H]JH I from binding sites was measured. The relative affinities were EFDA greater than JH I greater than JH II greater than JH III. When Scatchard analysis of the binding of [3H]EFDA or [3H]JH I to the larval JHBP was performed, an estimated apparent KD of 4.5 X 10(-8)M was found for EFDA, whereas for JH I a slightly higher KD of 8.8 X 10(-8) M was calculated. To determine if [3H]EFDA bound at the JH I binding site, displacement of [3H]JH I from the JHBP complex with unlabeled JH I, JH II, and JH III was compared to the displacement of [3H]EFDA with the same homologues. The results demonstrated that the photoaffinity label bound covalently at the JH I binding site on the hemolymph binding protein of Manduca sexta. Fluorescence autoradiography of [3H]EFDA photoaffinity labeled proteins separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed that [3H]EFDA bound covalently to two major proteins in the absence of JH I.(ABSTRACT TRUNCATED AT 250 WORDS)

Isolation of 2-fluorocitrate produced by in vivo dealkylation of 29-fluorostigmasterol in an insect

A novel pro-insecticide, 29-fluorostigmasterol, is proposed to cause mortality due to release of fluoroacetate during side chain dealkylation. The 29-3H-labeled substrate was fed to third instar tobacco hornworms (Manduca sexta) and erythro-2-fluoro-[2-3H] citrate was isolated in 0.012% yield by ion-exchange, silica gel, and reverse-phase chromatography of the tricarboxylic acid, trimethyl ester, and trimethyl ester benzoate, respectively. The less toxic 29-fluoro-[29-3H]sitosterol did not provide sufficient labeled fluorocitrate to allow isolation, while a more toxic 16-3H-labeled 16-fluorofatty acid gave nearly 1% conversion to labeled fluorocitrate. This is the first direct chemical evidence for the fate of the two carbons removed during phytosterol dealkylation in an insect. It is also the first use of labeled fluoroacetate precursors to identify labeled 2-fluorocitrate as an in vivo metabolite of these precursors.

A specific photoaffinity label for hemolymph and ovarian juvenile hormone-binding proteins in Leucophaea maderae

A tritium-labeled diazocarbonyl juvenile hormone (JH) analog, (10-[10,11-3H]epoxyfarnesyl diazoacetate, [3H]EFDA), covalently bound to proteins in both hemolymph and ovarian extracts when reaction mixtures were irradiated with UV light. The addition of various concentrations of unlabeled JH III selectively inhibited [3H]EFDA photoattachment to proteins. Using the Scatchard method of analysis, [3H]EFDA bound specifically and with relatively high affinity (KD = 1.5 X 10(-6) M) to a macromolecule in each extract, although nonspecific binding to other molecules was also present (20-50%). To determine if [3H]EFDA bound at the JH III-binding site on the binding proteins, radioactive [3H]JH III or [3H]EFDA was complexed with proteins in the presence of various concentrations of either unlabeled JH III or JH I under equilibrium conditions. The results demonstrated that the natural hormone, JH III, displaced both bound labeled ligands 4.1 +/- 0.5 times better than the homolog JH I. Thus, the photoaffinity label [3H]EFDA bound at the same site on the protein as [3H] JH III. Fluorescent autoradiography of [3H]EFDA-labeled proteins separated by sodium dodecyl sulfate electrophoresis revealed that several proteins in both hemolymph and ovarian extracts bound [3H]EFDA. To determine the specificity of binding, extracts were irradiated with UV light in the presence of unlabeled JH III and [3H]EFDA. The results demonstrated that JH III prevented photoattachment of [3H]EFDA to a major protein in each extract. The molecular weight of these proteins was estimated at approximately 200,000 for both the hemolymph protein and the ovarian protein.

Synthesis and bioassay of isoprenoid 3-alkylthio-1,1,1-trifluoro-2-propanones: potent, selective inhibitors of juvenile hormone esterase

Four 3-alkylthio-1,1,1-trifluoro-2-propanones with juvenile hormone-like side chains were prepared from citronellol and homogeraniol. These substrates were designed as possible transition-state analogs for the juvenile hormone (JH)-specific esterases present in insects. These four isoprenoid trifluormethyl ketones were assayed in vitro with JH esterase and general esterases from larvae of the cabbage looper, Trichoplusia ni (Lepidoptera, Noctuidae), and with eel acetylcholinesterase and bovine chymotrypsin. JH esterase inhibition I50 values were in the nanomolar range for all four compounds, while the other esterases had I50's which were 10(3) to 10(5) higher. The high selectivity of these inhibitors is believed to be due to their similarity in size and functionality to natural JH III. Treatment of T. ni larvae in vivo with solutions of the most active analog, 3-[(E)-4,8-dimethyl-3,7-nonadienylthio]-1,1,1-trifluoro-2-propanon e (DNTFP) causes a dose-dependent delay in pupation and a concurrent selective inhibition of JH esterase. These data support the hypothesis that the reduction in in vivo JH titer in larval T. ni is due, in part, to hydrolysis of the hormone by selective esterases. DNTFP appears to be competing with JH for the active site of JH esterase.

Side chain modified sterols as probes into insect molting hormone metabolism. II: synthesis of monofluorocholesterols

The hydroxylations of the cholesterol side chain at C-20, 22, and 25 are key terminal events in ecdysone biogenesis. We have prepared the C-20, C-22, C-24, and C-25 monofluorinated cholesterols as potential inhibitors of these hydroxylation events, and preliminary bioassay results in Manduca sexta are reported. The synthesis of [26(14)C]-20-fluorocholesterol is also described. Although the 20-, 22-, and 25-monofluorocholesterols do not appear to affect larval growth and development, the 24-fluoro isomer shows a moderate retardation of growth and a modest increase in mortality.