Insect Biochemistry最新文献

Members of the adipokinetic hormone/red pigment-concentrating hormone (AKH/RPCH) family characteristically cause metabolite mobilization by the insect fat body. The present study identified several additional physiological actions in adult Blaberus discoidalis cockroaches that were influenced by synthetic Blaberus hypertrehalosemic hormone (HTH) and other AKH/RPCH family peptides. HTH elevated blood carbohydrate by 4-fold and cytochrome heme a + b synthesis of fat body mitochondria by 3-fold. Both carbohydrate and heme synthesis were dose-responsive to HTH. Carbohydrate synthesis was 10 times more sensitive to HTH than heme synthesis. Heme synthesis was also stimulated by Periplaneta cardioacceleratory hormones (CAH)-I and -II and RPCH but not by AKH-I or -II, at the doses tested. HTH showed strong cardioexcitatory activity. Long-term treatment of decapitated female B. discoidalis with juvenile hormone analog (JHA = methoprene) stimulated by 2.6-fold the rate of synthesis of secreted fat body proteins. HTH enhanced the JHA-dependent export protein synthesis by 42% above that observed with JHA alone. SDS-PAGE demonstrated that JHA determined the nature of the newly synthesized polypeptides; HTH enhanced their synthesis rate. Neither AKH-I nor HTH affected protein synthesis when added directly to isolated fat body. These results demonstrate that peptides of the AKH/RPCH family have multiple physiological actions related to fat body energy metabolism.

Unlike some moths, pheromone production in Trichoplusia ni is not regulated by a pheromone activating neuropeptide. Rather, competency to produce pheromone apparently is linked with changes in the ecdysteroid titer that occur late in metamorphosis. In contrast to adult pheromone glands, glands from pharate adults 2 days before eclosion were non-competent, and (1) had undetectable levels of the pheromone, (Z)-7-dodecenyl acetate, and pheromone-specific intermediates, (2) showed little or no conversion of radiolabeled substrate to product in enzyme assays of fatty acid synthetase, Δ11 desaturase, and acetyltransferase, and (3) failed to incorporate radiolabeled acetate into pheromone in gland culture. Glands 1 day before adult eclosion exhibited low titers of pheromone and the intermediate, (Z)-11-hexadecenoate, and showed low levels of radiolabeled acetate incorporation into pheromone in gland culture. By the time of adult eclosion, the gland was fully competent. Precocious development of pheromone gland competency was induced by removing the head and thorax from pupae 2 days before adult eclosion. This effect appears to result from the reduction of ecdysteroid, since it was blocked by the administration of 20-hydroxyecdysone. This ability to manipulate the development of the pheromone gland was restricted to a critical period, since removal of head and thorax from younger pupae did not induce pheromone gland competency, and administration of 20-hydroxyecdysone to older pupae did not block its onset. In addition to differences in competency, early pharate and adult glands exhibited dissimilarities with respect to (1) the types of proteins synthesized in gland culture, and (2) the types of proteins translated from mRNA in vitro.

The isolated hindgut preparation of the cockroach, Leucophaea maderae has provided an effective bioassay tool for the isolation of certain structural types of insect myotropic peptides. Initially, the preparation was used to monitor excitatory and inhibitory activities of numerous HPLC fractions in a study that resulted in the structural characterization of 12 Leucophaea neuropeptides. Subsequently, the preparation was used as the bioassay for the isolation and structural characterization of myotropic neuropeptides of the house cricket, Acheta domesticus, and the locust, Locusta migratoria. Five novel myotropic peptides from the cricket were structurally characterized, and 32 separate myotropic compounds were isolated from nervous tissue of the locust. At present, 8 of the locust peptides have been structurally characterized. Isolation studies using this bioassay have been responsible for the discovery of 25 unique neuropeptides, 4 new peptide families, and the initial demonstration of the natural analog phenomenon in insects.

Four closely related eclosion hormones (EHs), EH-I, -II, -III and -IV, were purified from 770,000 pharate adult heads of the silkworm, Bombyx mori. The complete amino acid sequence was determined by Edman degradation of peptide fragments generated by enzymatic digestion. Preliminary results have been reported (Kono et al., Agric. biol. Chem.51, 2307–2308, 1987). Accumulated data suggested that EH-IV has the longest sequence consisting of 62 residues. EH-I and -III have N-termini truncated by two residues. EH-I and -II terminate at position 61. The removal of the C-terminal leucine in EH-I and -II might have occurred artificially during extraction.

An ovulation stimulating substance (OSS) was isolated from males of the fruit fly Drosophila suzukii, and purified to a homogeneous state by a 5-step purification procedure: extraction with 80% methanol, chloroform wash, heat treatment, ion-exchange chromatography, and reverse phase high performance liquid chromatography. Approximately 100-fold purification was obtained thereby yielding 39 μg of OSS from 1000 males for an overall yield of 34%. The OSS is a single peptide consisting of at least 35 amino acid residues and having a molecular weight of 3990. The purified OSS not only initiated ovulation in unmated females but also suppressed their receptivity towards males. The peptide of D. suzukii was found to be effective in the females of D. melanogaster, a species that belong to a different subgroup, but was less effective in a more closely related species, D. pulchrella.

Phospholipase A₂ from the venom of the European honeybee (Apis mellifera) consists of three isoforms with approximate molecular masses of 16, 18, and 20 kDa, respectively, as deduced from SDS-PAGE. These variants, termed PLA-16, PLA-18, and PLA-20, were isolated by lectin affinity chromatography and preparative polyacrylamide gel electrophoresis. The amino acid sequences of the N-terminal peptide portions of all three isoforms, as assessed by automated Edman degradation, were identical with that expected for honeybee phospholipase A₂. Sequencing data suggest that, while PLA-18 and PLA-20 carry oligosaccharide residues at asparagine-13, PLA-16 has escaped glycosylation during biosynthesis. Release of the carbohydrate from PLA-18 and PLA-20 with peptide: N-glycosidase F abolished the molecular mass differences between the three isoforms of phospholipase. Differences in sensitivity to α-mannosidase and monosaccharide composition of PLA-18 and PLA-20 further indicate that their electrophoretic separation is based on structural features of the N-glycosidically linked oligosaccharide. Noticeably, PLA-20 contains N-acetylgalactosamine, a sugar not having yet been described as a constituent of insect glycoproteins.