摘要:

AbstractWe studied the metabolism of [U‐14C]isoleucine by intact and homogenized corpora allata (CA) from various insect species to determine how this substrate is converted to precursors of juvenile hormone (JH). CA homogenates of the lepidopteransManduca sexta, Hyalophora cecropia, andSamia cynthiametabolize [U‐14C]isoleucine to several products including 2‐keto‐3‐methyl‐valerate, 2‐methylbutyrate, CO2, propionate, and acetate. Intact CA of maleH. cecropiaproduce particularly high levels of 2‐keto‐3‐methylvalerate, indicating a highly active branched‐chain‐amino acid transaminase. In contrast, CA homogenates from the nonlepidopteransPeriplaneta americana, Schistocerca nitens, Tenebrio molitor, andDiploptera punctatabarely metabolize [U‐14C]isoleucine. However,P. americanaCA homogenate metabolizes [U‐14C]2‐keto‐3‐methylvalerate, the transamination product of [U‐14C]isoleucine, more rapidly than does a homogenate ofM. sextaCA. Furthermore, intact CA fromP. americanaincubated with [U‐14C]2‐keto‐3‐methylvalerate incorporate low levels of14C into JH III, but do not metabolize this substrate to JH II or JH I. Intact CA from femaleDiploptera punctataproduce very high levels of JH III, but are also unable to incorporate radiolabel from [U‐14C]isoleucine into JH III, which substantiates our findings with other nonlepidopteran CA. The results suggest that CA of nonlepidopteran insects lack an active branched‐chain amino acid transaminase and, consequently, are unable

ISSN:0739-4462    

DOI:10.1002/arch.940190102

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractToxicological and neurophysiological studies were performed to characterize the resistance mechanism in a cyclodiene‐resistant strain ofDrosophila melanogaster(Maryland strain). Dieldrin had an LC50of 0.058 ppm against the larvae of susceptibleD. melanogaster(Oregon‐R wild type) when formulated in the rearing media. The LC50of the resistant Maryland strain was 10.8 ppm, giving a resistance ratio (LC50‐Maryland/LC50‐susceptible) of 186‐fold. Suction electrode recordings were made from peripheral nerves of the larval central nervous system of test whether reduced nerve sensitivity played any role in the observed resistance. In susceptible preparations (n = 5), inhibition of nerve firing by 1 mM γ‐aminobutyric acid (GABA) was effectively antagonized within 3–10 min by 10 μM dieldrin. In contrast, 30 min incubations with 10 μM dieldrin had no effect on preparations from cyclodiene‐resistant individuals (n = 5). Similarly, 10 μM picrotoxinin blocked GABA‐dependent inhibition in susceptible nerve preparations (n = 3). In recordings from resistant insects (n = 4), picrotoxinin displayed either weak antagonism of GABA or hyperexcitation indistinguishable from susceptible preparations. These results demonstrate that cyclodiene resistance in the Maryland strain ofD. melanogaster(1) is expressed in immature stages, (2) is present at the level of the nerve, and (3) extends to picrotoxinin, albeit at a reduced level compared with dieldrin. The possible role of an altered GABA receptor in this re

ISSN:0739-4462    

DOI:10.1002/arch.940190103

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractWe provide evidence of an important role for ascorbate free radical (AFR) reductase, dehydroascorbate (DHA) reductase, glutathione, and glutathione reductase as components of an oxidant‐scavenging system in the midgut of larvalHelicoverpa zea. Also, midgutortho‐quinone reductase is a potentially important constituent of the protective system against quinones. The midgut activities of AFR reductase, DHA reductase, glutathione reductase, andortho‐quinone reductase were, respectively, 168, 22.1, 6, and 39.5 nmol/min/mg protein. The relatively high activity of these enzymes in the midgut provides circumstantial evidence for a protective mechanism utilizing ascorbate as an antioxidant and glutathione and/or NADPH as reductants. To our knowledge, the enzymes AFR reductase and DHA reductase have not been reported in insects. The particular relevance of this system to antioxidant protection, and in particular to the detoxication of quinones formed in damaged leaf tissues, is disc

ISSN:0739-4462    

DOI:10.1002/arch.940190104

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractThe expression of alaserpin, a serine protease inhibitor, was studied in the developing adult olfactory system ofManduca sexta. Alaserpin mRNA in the antenna was identical to alaserpin from larval fat body, by restriction mapping and partial sequencing of clones isolated from a male pupal stage 6 antennal cDNA library. Northern and primer extension analysis showed that alaserpin transcripts were the same length at all stages and were present at stages 3 and 6, declined at stages 9–15, reappeared at stage 18, and persisted in adults. Western blotting revealed that alaserpin was present at stages 3–12, declined at stage 15, and disappeared at stage 18 and in adults. Immunocytochemistry at stage 6 revealed labeled cells closely associated with neurite bundles and scattered throughout the receptor cell layer. An occasional cell was seen in the antennal lumen. Labeled cells were segmentally distributed along the length of the antenna. The results suggest that alaserpin may have a role in antennal morphogenesis and olfactory neuron axon outgro

ISSN:0739-4462    

DOI:10.1002/arch.940190105

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractOur discovery of a Mr128 k biotin‐containing protein in an extract of the white‐fly was an unexpected outcome of the use of an avidin‐biotin‐peroxidase method to visualize a western blot. This major biotin‐containing protein was shown to be present in several tissues of 10 different species of insects by doing a western blot and staining it with streptavidin‐linked peroxidase. The amount of this protein in the thorax of the mosquito,Aedes aegypti, increased during development. The non‐flying grasshopper,Barytettix psolus, had reduced amounts of this protein in their thoraces compared to a flying grass‐hopper,Schistocerca americana. The major biotin‐containing protein was purified from the thoraces of honeybee,Apis mellifera, using an avidin Sepharose affinity column. The purified biotin‐containing protein was shown to be pyruvate carboxylase, an enzyme that catalyzes the specific transfer of a carboxyl group to pyruvate, yielding oxaloacetate. The purified honeybee pyruvate carboxylase was characterized enzymatically and structurally. This protein had a single subunit of Mr128 k and formed a native molecule of about Mr500 k consisting of four of these subunits. The amino acid composition of the protein was also obtained. The enzymatic activity of this protein required acetyl‐CoA, ATP, and Mg2+. The Kms of the enzyme for bicarbonate and pyruvate were similar to pyruvate carboxylase from other oganisms. The biotin‐containing protein was also partially purified from mosquito thoraces using the same methods and was shown to be pyruvate carboxylase. The comparison between insect pyruvate carboxylase and that of other organisms is provided and the possible physiological role of the pyruvate carboxylase in the thoracic muscles

ISSN:0739-4462    

DOI:10.1002/arch.940190106

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

ISSN:0739-4462    

DOI:10.1002/arch.940190107

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

ISSN:0739-4462    

DOI:10.1002/arch.940190101

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY