A specific affinity reagent to distinguish aldehyde dehydrogenases and oxidases. Enzymes catalyzing aldehyde oxidation in an adult moth

Aldehyde dehydrogenase (ALDH) and oxidase (AO) enzymes from the tissue extracts of male and female tobacco budworm moth (Heliothis virescens) were identified after electrophoretic protein separation. AO activity was visualized using formazan- or horseradish peroxidase-mediated staining coupled to the AO-catalyzed oxidation of benzaldehyde. A set of six soluble AO enzymes with isoelectric points from pI 4.6 to 5.3 were detected primarily in the antennal extracts. Partially purified antennal AO enzymes also oxidized both (Z)-9-tetradecenal and (Z)-11-hexadecenal, the two major pheromone components of this moth. ALDH activity was detected using a tritium-labeled affinity reagent based on a known irreversible inhibitor of this enzyme. This labeled vinyl ketone, [3H](Z)-1,11-hexadecadien-3-one, was synthesized and used to covalently modify the soluble ALDH enzymes from tissue extracts. Molecular subunits of potential ALDH enzymes were visualized in the fluorescence autoradiograms of sodium dodecyl sulfate-polyacrylamide gel electrophoresis-separated proteins of the antenna, head, and leg tissues. Covalent modification of these protein subunits decreased specifically in the presence of excess pheromone aldehyde or benzaldehyde. Labeled vinyl ketones are thus novel tools for the identification of molecular subunits of ALDH enzymes.     

Aldehyde-oxidizing enzymes in an adult moth: in vitro study of aldehyde metabolism in Heliothis virescens

The conversion of pheromonal aldehydes to carboxylic acids in vitro in tissue extracts of Heliothis virescens is catalyzed by both aldehyde dehydrogenase and aldehyde oxidase enzymes. The aldehyde-oxidizing activity in antennae, heads, legs, and hemolymph from male and female moths was examined by radiochromatographic and spectroscopic assays. First, the enzymatic activity was measured in the presence or absence of added NAD+ using either (Z)-9-tetradecenal or (Z)-11-hexadecenal as tritiated substrate. Second, substrate specificity was determined spectroscopically by (i) indirect measurement of the AO-released hydrogen peroxide through the coupled AO-horseradish peroxidase reaction and by (ii) direct measurement of the ALDH-produced NADH. Both aldehyde-oxidizing activities were associated with soluble enzymes in the antennal extracts, and these enzymes degraded pheromone and nonpheromonal aldehydes. Both AO and ALDH activities were present in male and female tissues. AO activity was exhibited primarily in the antennal extracts and to a lesser degree in the leg extracts. Moreover, ALDH activity was distributed in the antenna, head, and leg extracts. A vinyl ketone analog of (Z)-11-hexadecenal preferentially inhibited the ALDH activity over the AO activity.     

Interaction of human aldehyde dehydrogenase with aromatic substrates and ligands

The substrate benzaldehyde (but not propionaldehyde) could elute aldehyde dehydrogenase from a p-hydroxyacetophenone-affinity column, and inhibit the esterase activity (K_i=47 μM), indicating that this simple aromatic aldehyde binds to the free enzyme and possibly in the substrate-binding site. Thus, the kinetic mechanism for aldehyde dehydrogenase might be dependent upon which aldehyde is used in the reaction. Chloramphenicol which also elutes the enzyme from the affinity column, shows a discriminatory effect by inhibiting the ALDH1 oxidation of benzaldehyde and activating that of propionaldehyde while showing no effect when assayed with hexanal or cyclohexane–carboxaldehyde. Chloramphenicol is an uncompetitive inhibitor against NAD when benzaldehyde is the substrate. We propose that this drug might interact with both the benzaldehyde and NAD binding sites.     

Cloning,expression and characterization of a novel aldehyde dehydrogenase gene from Flammeovirga pacifica

A novel putative aldehyde dehydrogenase (ALDH) gene aldh1413 from Flammeovirga pacifica isolated from deep sea sediment was cloned, expressed, and characterized. The molecular weight of the ALDH1413 (479 amino acids) was estimated by SDS-PAGE to be 53 kDa. The optimum temperature and pH for ALDH1413 were 35°C and 9.0, respectively. In the presence of either NAD⁺ or NADP⁺, the enzyme could oxidize a number of aliphatic aldehydes, particularly C3-and C5-aliphatic aldehydes and aromatic aldehydes such as benzaldehyde, which indicates that the enzyme belongs to broad-specific (ALDH) superfamily. Steady-state kinetic study revealed that ALDH1413 had a K _M value of 0.545 mM and a k _cat value of 7.48 s^?1 when propionaldehyde was used as the substrate. The Na⁺ could enhance ALDH1413 activity, which indicated it might be adapt to its habitat, marine environment.     

γ-aminobutyric acid in the central nervous system of metamorphosing and mature Manduca sexta

We have begun to examine the factors controlling the accumulation of the neurotransmitter γ-aminobutyric acid (GABA) in the central nervous system (CNS) of the sphinx moth Manduca sexta. Analysis of soluble amino acids in CNS structures from mature moths outlines the regional distribution of GABA. Analysis of amino acids in the antennal lobes (the primary olfactory centres) of Manduca during metamorphosis reveals that GABA accumulates gradually and continuously through most of adult development until eclosion; within 18 hr after eclosion, levels of GABA abruptly increase 27–50%. The activity of the biosynthetic enzyme glutamic acid decarboxylase (EC 4.1.1.15), assayed in extracts of antennal lobes from developing moths, does not change after eclosion. Extracts of hemolymph from mature moths contain low levels of glutamate ( <0.2 mM) and higher levels of certain other amino acids such as serine, glutamine and proline. The concentration of proline in hemolymph increases up to 2-fold after eclosion. Glutamate, glutamine and proline are interconvertible in the CNS, and each can serve as precursor for GABA synthesis both in vivo and in vitro. The efficiency of the precursor role in vitro is similar for each amino acid, as estimated from the ratio of the specific radioactivities of GABA and glutamic acid in the ganglion derived from each precursor. Exogenous proline and glutamine can equilibrate rapidly with the ganglionic pools of the same amino acids while glutamic acid is relatively excluded. Taken together, the findings of this study show that proline and glutamine may contribute substantially to synthesis of GABA in the CNS of M. sexta.     

Saxitoxin binding to neural membranes from pyrethroid susceptible and resistant tobacco budworm moths Heliothis virescens

1. [³H]Saxitoxin, a sodium channel probe, was found to bind reversibly with high affinity to a single class of noninteracting sites in membrane preparations from whole head homogenates of tobacco budworm, Heliothis virescens (F.), moths from a pyrethroid susceptible strain and from a pyrethroid resistant strain with nerve insensitivity and metabolic resistance mechanisms.2. No significant interstrain differences were detected in saturation (K_D, B_max) and kinetic (k₊₁, k₋₁) experiments.3. Also, five pyrethroids, two formamidines, and DDT had no significant effect on [³H]saxitoxin binding when tested at concentrations of 1 × 10⁻⁴ and 1 × 10⁻⁸ M.4. It appeared that a decreased density in sodium channels in resistant strain moths as compared with that in susceptible strain moths was not a factor in pyrethroid-induced resistance in this particular strain of tobacco budworm.     

Characterization of Xenopus cytosolic thyroid-hormone-binding protein (xCTBP) with aldehyde dehydrogenase activity

Multiple cytosolic thyroid-hormone-binding proteins (CTBPs) with varying characteristics, depending on the species and tissue, have been reported. We first purified a 59-kDa CTBP from Xenopus liver (xCTBP), and found that it is responsible for major [¹²⁵I]T₃-binding activity in Xenopus liver cytosol. Amino acid sequencing of internal peptide fragments derived from xCTBP demonstrated high identity to the corresponding sequence of mammalian aldehyde dehydrogenases 1 (ALDH1). To confirm whether or not xCTBP is identical to xALDH1, we isolated cDNAs encoding xALDH1 from an adult Xenopus hepatic cDNA library. The amino acid sequences deduced from the two isolated xALDH1 cDNAs were very similar to those of mammalian ALDH1 enzymes. The recombinant xALDH1 protein exhibited both T₃-binding activity and ALDH activity converting retinal to retinoic acid (RA), which were similar to those of xCTBP purified from liver cytosol. The T₃-binding activity was inhibited by NAD, while the ALDH activity was inhibited by thyroid hormones. Our results demonstrate that xCTBP is identical to ALDH1 and suggest that this protein might modulate RA synthesis and intracellular concentration of free T₃. Communications between thyroid hormone and retinoid pathways are discussed.     

O-Methylation of benzaldehyde derivatives by "lignin specific" caffeic acid 3-O-methyltransferase

Although S-adenosyl-l-methionine (SAM) dependent caffeic acid/5-hydroxyferulic acid 3/5-O-methyltransferase (COMT) is one of the key enzymes in lignin biosynthesis, the present work demonstrates that alfalfa COMT methylates benzaldehyde derivatives more efficiently than lignin pathway intermediates. 3,4-Dihydroxy, 5-methoxybenzaldehyde and protocatechuic aldehyde were the best in vitro substrates for OMT activity in extracts from developing alfalfa stems, and these compounds were preferred over lignin pathway intermediates for 3-O-methylation by recombinant alfalfa COMT expressed in Escherichia coli. OMT activity with benzaldehydes was strongly reduced in extracts from stems of transgenic alfalfa down-regulated in COMT. However, although COMT down-regulation drastically affects lignin composition, it does not appear to significantly impact metabolism of benzaldehyde derivatives in alfalfa. Structurally designed site-directed mutants of COMT showed altered relative substrate preferences for lignin precursors and benzaldehyde derivatives. Taken together, these results indicate that COMT may have more than one role in phenylpropanoid metabolism (but probably not in alfalfa), and that engineered COMT enzymes could be useful for metabolic engineering of both lignin and benzaldehyde-derived flavors and fragrances.     

蛾类昆虫性信息素生物合成的研究进展

综述了各种不同化学结构类型的蛾类雌性信息素生物合成途径。此外还叙述了特定比例的性信息素成分在雌蛾体内产生的机理以及某些蛾类中信息素生物合成酶类与物种进化间的关系。     

Diastereoselective Synthesis of a Lilac Aldehyde Isomer and Its Electrophysiological Detection by a Moth

The monoterpene lilac aldehyde (=2‐(5‐ethenyl‐5‐methyloxolan‐2‐yl)propanal) is a widespread flower scent. Lilac aldehyde is emitted in high amounts from nocturnal plant species, and it is highly attractive to nocturnal moth pollinators, such as Hadena bicruris, the pollinating seed predator of Silene latifolia. Lilac aldehyde possesses three stereogenic centers and can occur in eight stereoisomers which induce different antennal responses in H. bicruris. The distribution pattern of stereoisomers differs among plant species, and if H. bicruris has different receptors for detecting different isomers, it may use these differences to discriminate flowers of S. latifolia hosts from flowers of non‐host plants. To investigate the question whether the moths have in their antennae one olfactory receptor or several different receptors for the detection of the single lilac aldehyde isomers, (2S,2′S,5′S)‐lilac aldehyde was diastereoselectively synthesized. (2S,2′S,5′S)‐Lilac aldehyde and its isomeric mixture were tested electrophysiologically on antennae of H. bicruris. The results displayed antennal responses, which are characteristic for a single receptor that detects the different lilac aldehyde isomers.     

Crystal Structure of Aldehyde Dehydrogenase 16 Reveals Trans-Hierarchical Structural Similarity and a New Dimer

The aldehyde dehydrogenase (ALDH) superfamily is a vast group of enzymes that catalyze the NAD⁺-dependent oxidation of aldehydes to carboxylic acids. ALDH16 is perhaps the most enigmatic member of the superfamily, owing to its extra C-terminal domain of unknown function and the absence of the essential catalytic cysteine residue in certain non-bacterial ALDH16 sequences. Herein we report the first production of recombinant ALDH16, the first biochemical characterization of ALDH16, and the first crystal structure of ALDH16. Recombinant expression systems were generated for the bacterial ALDH16 from Loktanella sp. and human ALDH16A1. Four high-resolution crystal structures of Loktanella ALDH16 were determined. Loktanella ALDH16 is found to be a bona fide enzyme, exhibiting NAD⁺-binding, ALDH activity, and esterase activity. In contrast, human ALDH16A1 apparently lacks measurable aldehyde oxidation activity, suggesting that it is a pseudoenzyme, consistent with the absence of the catalytic Cys in its sequence. The fold of ALDH16 comprises three domains: NAD⁺-binding, catalytic, and C-terminal. The latter is unique to ALDH16 and features a Rossmann fold connected to a protruding β-flap. The tertiary structural interactions of the C-terminal domain mimic the quaternary structural interactions of the classic ALDH superfamily dimer, a phenomenon we call “trans-hierarchical structural similarity.” ALDH16 forms a unique dimer in solution, which mimics the classic ALDH superfamily dimer-of-dimer tetramer. Small-angle X-ray scattering shows that human ALDH16A1 has the same dimeric structure and fold as Loktanella ALDH16. We suggest that the Loktanella ALDH16 structure may be considered to be the archetype of the ALDH16 family.     

Sensory processing of ambient CO<Subscript>2</Subscript> information in the brain of the moth<Emphasis Type="Italic"> Manduca sexta</Emphasis>

Insects use information about CO₂ to perform vital tasks such as locating food sources. In certain moths, CO₂ is involved in oviposition behavior. The labial palps of adult moths that feed as adults have a pit organ containing sensory receptor cells that project into the antennal lobes, the sites of primary processing of olfactory information in the brain. In the moth Manduca sexta and certain other species of Lepidoptera, these receptor cells in the labial-palp pit organ have been shown to be tuned to CO₂, and their axons project to a single, identified glomerulus in the antennal lobe, the labial-palp pit organ glomerulus. At present, however, nothing is known about the function of this glomerulus or how CO₂ information is processed centrally. We used intracellular recording and staining to reveal projection (output) neurons in the antennal lobes that respond to CO₂ and innervate the labial-palp pit organ glomerulus. Our results demonstrate that this glomerulus is the site of first-order processing of sensory information about ambient CO₂. We found three functional types of CO₂-responsive neurons (with their cell bodies in the antennal lobe or the protocerebrum) that provide output from the antennal lobe to higher centers in the brain. Some physiological characteristics of those neurons are described.Abbreviations AL Antennal lobe - AN Antennal nerve - CMB Calyces of the mushroom body - IPSP Inhibitory postsynaptic potential - LC-I Dorsal cluster of the lateral group of AL neuronal somata - LH Lateral horn of the protocerebrum - LPN Labial-palp nerve - LPO Labial-palp pit organ - LPOG LPO glomerulus - PC Protocerebrum - PI AL neuron that projects to the PC through the inner antenno-cerebral tract - PN Projection neuron     

Expression of a GABAB - Receptor in Olfactory Sensory Neurons of Sensilla trichodea on the Male Antenna of the Moth Heliothis virescens

In the olfactory pathway of Drosophila, a GABA_B receptor mediated presynaptic gain control mechanism at the first synapse between olfactory sensory neurons (OSNs) and projection neurons has been suggested to play a critical role in setting the sensitivity and detection range of the sensory system. To approach the question if such a mechanism may be realized in the pheromone recognition system of male moths in this study attempts were made to explore if moth''s pheromone-responsive cells express a GABA_B- receptor. Employing a combination of genome analysis, RT-PCR experiments and screening of an antennal cDNA library we have identified a cDNA which encodes the GABA_B-R1 receptor of Heliothis virescens. Moreover, based on the HvirGABA_B-R1 sequence we could predict a GABA_B-R1 protein from genome sequences of the silkmoth Bombyx mori. To assess whether HvirGABA_B-R1 is expressed in OSNs of male antenna we performed whole-mount in situ hybridization (WM-ISH) experiments. Several HvirGABA_B-R1 positive cells were visualized under long sensilla trichodea, known to contain pheromone-responsive OSNs. In parallel it was shown that cells under long trichoid hairs were labelled with pheromone receptor specific probes. In addition, the HvirGABA_B-R1 specific probe also labelled several cells under shorter olfactory sensilla, but never stained cells under mechanosensory/gustatory sensilla chaetica. Together, the results indicate that a GABA_B receptor is expressed in pheromone-responsive OSNs of H. virescens and suggest a presynaptic gain control mechanism in the axon terminals of these cells.     

Aldehyde oxidase generates deoxyribonucleic acid single strand nicks in vitro

SUMMARY

We purified aldehyde oxidase (AO) from rabbit livers and found that AO produced deoxyribonucleic acid (DNA) single strand nicks in vitro. Acetaldehyde, benzaldehyde, and certain purine bases were effective substrates for AO catalyzed DNA strand nicking. DNA strand nicking did not occur with the reducing substrates nicotinamide-adenine dinucleotide or dithionite that produce superoxide anion (O_2′^?). Inclusion of electron transport inhibitors, potassium cyanide, ferricyanide or menadione, prevented AO catalyzed nicking. AO induced DNA strand nicking was dependent upon hydrogen peroxide (H₂O₂) formation and most likely generation of hydroxyl radical (HO'). The present observations may be pertinent to the recently proposed involvement of AO in inherited juvenile familial amyotrophic lateral sclerosis (JFALS) and other oxygen radical mediated diseases.     

Enhanced Benzaldehyde Tolerance in Zymomonas mobilis Biofilms and the Potential of Biofilm Applications in Fine-Chemical Production

Biotransformation plays an increasingly important role in the industrial production of fine chemicals due to its high product specificity and low energy requirement. One challenge in biotransformation is the toxicity of substrates and/or products to biocatalytic microorganisms and enzymes. Biofilms are known for their enhanced tolerance of hostile environments compared to planktonic free-living cells. Zymomonas mobilis was used in this study as a model organism to examine the potential of surface-associated biofilms for biotransformation of chemicals into value-added products. Z. mobilis formed a biofilm with a complex three-dimensional architecture comprised of microcolonies with an average thickness of 20 μm, interspersed with water channels. Microscopic analysis and metabolic activity studies revealed that Z. mobilis biofilm cells were more tolerant to the toxic substrate benzaldehyde than planktonic cells were. When exposed to 50 mM benzaldehyde for 1 h, biofilm cells exhibited an average of 45% residual metabolic activity, while planktonic cells were completely inactivated. Three hours of exposure to 30 mM benzaldehyde resulted in sixfold-higher residual metabolic activity in biofilm cells than in planktonic cells. Cells inactivated by benzaldehyde were evenly distributed throughout the biofilm, indicating that the resistance mechanism was different from mass transfer limitation. We also found that enhanced tolerance to benzaldehyde was not due to the conversion of benzaldehyde into less toxic compounds. In the presence of glucose, Z. mobilis biofilms in continuous cultures transformed 10 mM benzaldehyde into benzyl alcohol at a steady rate of 8.11 g (g dry weight)⁻¹ day⁻¹ with a 90% molar yield over a 45-h production period.     

Dynamic Properties of Endogenous Phytochrome A in Arabidopsis Seedlings

The flacca tomato (Lycopersicon esculentum) mutant displays a wilty phenotype as a result of abscisic acid (ABA) deficiency. The Mo cofactor (MoCo)-containing aldehyde oxidases (AO; EC 1.2.3.1) are thought to play a role in the final oxidation step required for ABA biosynthesis. AO and related MoCo-containing enzymes xanthine dehydrogenase (XDH; EC 1.2.1.37) and nitrate reductase (EC 1.6.6.1) were examined in extracts of the flacca tomato genotype and of wild-type (WT) roots and shoots. The levels of MoCo were found to be similar in both genotypes. No significant XDH or AO (MoCo-containing hydroxylases) activities were detected in flacca leaves; however, the mutant exhibited considerable MoCo-containing hydroxylase activity in the roots, which contained notable amounts of ABA. Native western blots probed with an antibody to MoCo-containing hydroxylases revealed substantial, albeit reduced, levels of cross-reactive protein in the flacca mutant shoots and roots. The ABA xylem-loading rate was significantly lower than that in the WT, indicating that the flacca is also defective in ABA transport to the shoot. Significantly, in vitro sulfurylation with Na₂S reactivated preexisting XDH and AO proteins in extracts from flacca, particularly from the shoots, and superinduced the basal-level activity in the WT extracts. The results indicate that in flacca, MoCo-sulfurylase activity is impaired in a tissue-dependent manner.     

Kinetic evidence for human liver and stomach aldehyde dehydrogenase-3 representing an unique class of isozymes

Substrate and coenzyme specificities of human liver and stomach aldehyde dehydrogenase (ALDH) isozymes were compared by staining with various aldehydes including propionaldehyde, heptaldehyde, decaldehyde, 2-furaldehyde, succinic semialdehyde, and glutamic -semialdehyde and with NAD⁺ or NADP⁺ on agarose isoelectric focusing gels. ALDH3 isozyme was isolated from a liver via carboxymethyl-Sephadex and blue Sepharose chromatographies and its kinetic constants for various substrates and coenzymes were determined. Consistent with the previously proposed genetic model for human ALDH3 isozymes (Yinet al., Biochem. Genet. 26:343, 1988), a single liver form and multiple stomach forms exhibited similar kinetic properties, which were strikingly distinct from those of ALDH1, ALDH2, and ALDH4 (glutamic -semialdehyde dehydrogenase). A set of activity assays using various substrates, coenzymes, and an inhibitor to distinguish ALDH1, ALDH2, ALDH3, and ALDH4 is presented. As previously reported in ALDH1 and ALDH2, a higher catalytic efficiency (V _max/K _m) for oxidation of long-chain aliphatic aldehydes was found in ALDH3, suggesting that these enzymes have a hydrophobic barrel-shape substrate binding pocket. Since theK _m value for acetaldehyde for liver ALDH3, 83 mM, is very much higher than those of ALDH1 and ALDH2, ALDH3 thus represents an unique class of human ALDH isozymes and it appears not to be involved in ethanol metabolism.This work was supported by grants from the National Science Council and the Academia Sinica, Republic of China.     

In vitro hormonal stimulation of [14C]acetate incorporation by Heliothis armigera pheromone glands

Isolated pheromone gland preparations of Heliothis armigera incorporateradioactivity from [¹⁴C]sodium acetate at a linear rate for 24 h when incubated in a physiological saline. This incorporation is stimulated when methanolic or partially purified brain-complex extracts are present in the incubation medium and the stimulation is dose-dependent. The radioactive products extracted from the pheromone glands and media by hexane, revealed incorporation of radioactivity into a product exhibiting the same mobility as (Z)-11 hexadecenal, the main component of the pheromone of H. armigera, as analyzed by thin layer chromatography (TLC) and high pressure liquid chromatography (HPLC). In addition, gas chromatographic (GC) analysis of the hexane soluble products after incubation in the absence of [¹⁴C]sodium acetate revealed a significant stimulation of the concentration of (Z)-11 hexadecenal by brain-complex extracts.     

QTL analysis of sex pheromone blend differences between two closely related moths: Insights into divergence in biosynthetic pathways

To understand the evolution of premating signals in moths, it is important to know the genetic basis of these signals. We conducted Quantitative Trait Locus (QTL) analysis by hybridizing two noctuid moth species, Heliothis virescens (Hv) and Heliothis subflexa (Hs), and backcrossing the F₁ females to males of both parental species. One of these backcrosses (F₁ × Hs) was a biological replicate of our previous study (Sheck et al., 2006) and served to test the robustness of our previous findings. The backcross to Hv was designed to reveal QTL with recessive inheritance of the Hv character state. This study confirms previously discovered QTL, but also reports new QTL. Most importantly, we found relatively large QTL affecting Z9-16:Ald, the critical sex pheromone component of Hs. For Z9-14:Ald, the critical sex pheromone component of Hv, as well as for the minor pheromone compound 14:Ald, we found QTL in which the change in pheromone ratio was opposite-to-expected. Linking QTL to the biosynthetic pathways of the pheromone compounds of Hv and Hs implicates several candidate genes in the divergence of these premating signals, the most important of which are acetyl transferase, one or more desaturase(s), and a fatty acyl reductase or alcohol oxidase.     

Acetylcholine and its metabolic enzymes in developing antennae of the moth, Manduca sexta.

Antennae of the moth, Manduca sexta, are thickly populated with sensory neurons, which send axons through antennal nerves to the brain. These neurons arise by cell divisions and differentiate synchronously during the 18 days of metamorphosis from pupa to adult. Biochemical studies support the hypothesis that antennal neurons use acetylcholine (ACh) as a neurotransmitter: (1) Antennae incubated with [¹⁴C]choline synthesize and store [¹⁴C]ACh; several other transmitter candidates do not accumulate detectably when appropriate radioactive precursors are supplied; (2) antennae and antennal nerves contain endogenous ACh; and (3) extracts of mature antennae contain choline acetyltransferase (ChAc) and acetylcholinesterase (AChE) with properties similar to those reported for the enzymes from other arthropods. Levels of ACh, ChAc, and AChE begin to increase in antennae soon after the sensory neurons are “born.” Levels rise exponentially for over a week as the neurons differentiate and then reach a plateau, at about the time the neurons reach morphological maturity, that is maintained into adulthood. In contrast, levels of carnitine acetyltransferase, cholinesterase, and soluble protein, presumably not confined to nervous tissue, change little during metamorphosis. Levels of ACh, ChAc, and AChE rise in an intracranial segment of antennal nerve at about the same time as in the antenna, indicating that axons can transport neurotransmitter machinery at an early stage in their development.