Insect Biochemistry最新文献

The major yolk proteins were purified from the eggs of the hard tick, Dermacentor variabilis using gel filtration and ion exchange chromatography. Two vitellin proteins were identified and designated vitellin A (480 kilodaltons; kDa) and vitellin B (370 kDa). The isolectric points were pH 6.1 and 6.25, respectively. The absorption maxima for both proteins were 280 and 400 nm. The buoyant density of vitellin A was 1.281 g/ml and vitellin B 1.278 g/ml. The vitellins were hemoglycolipoproteins as indicated by selective staining of polyacrylamide gels, carbohydrate analyses and lipid analyses. Under reducing conditions (SDS-PAGE), vitellin A had eight major polypeptides at 135, 110, 98, 80, 67, 50, 45, and 35 kDa. Vitellin B was identical to vitellin A with the addition of a 93 kDa subunit. The only carbohydrate detectable in the proteins was mannose. The neutral lipids detected in both proteins were cholesteryl esters, triglycerides, free fatty acids and their methyl esters, and cholestrol. The only detectable phospholipid in both proteins was phosphatidylethanolamine. The purified vitellins were immunologically identical to female hemolymph proteins but not to host hemoglobin. Antivitellin antibodies to vitellin were used to identify possible locations of vitellogenin in the organs of ovipositing females.

Properties of glucose-6-phosphate dehydrogenase were assessed from the larvae of three insect species, the freeze tolerant Eurosta solidaginis, the freeze avoiding Epiblema scudderiana, and warm-acclimated Tenebrio molitor. Maximal enzyme activities were 16–17 fold higher in the cold hardy larvae than in T. molitor in line with the key role of G6PDH in providing NADPH for the synthesis of cryoprotectant polyols in these species. K_m values for glucose-6-P and NADP were determined at both high (24°C) and low (4°C) temperatures for all three enzymes. Temperature decrease had the greatest effect on T. molitor G6PDH increasing K_m glucose-6-P by 3-fold and K_m NADP by 2-fold; K_m values for G6PDH from the cold hardy species were less temperature-sensitive. The addition of polyols (glycerol, sorbitol) or KCl caused selected changes in the K_m values for both substrates in all species. Cryoprotectant action in the freezing protection of G6PDH was also examined, comparing G6PDH from E. solidaginis, E. scudderiana and yeast. A range of polyols (glycerol, sorbitol), other carbohydrates (trehalose, glucose, lactate) and amino acids (alanine, glutamate, proline) were effective in protecting activity during freezing. Without cryoprotectant, enzyme activity after 1 h freezing at −77°C was <10% compared to controls. Low concentrations of protectants (typically <50 mM) gave complete protection during freezing. Values for cryoprotectant concentrations giving half-maximal recovery of activity ranged from as low as 7–10 mM for trehalose to 20–25 mM for most other compounds.

The conversion of acetyl-CoA to HMG-CoA was measured by a radioenzymatic assay in which the product is derivatized to its bis(p-nitrobenzyl)ester and separated from the substrate by TLC. The enzymatic assay was applied to post-mitochondrial supernatants of corpora allata homogenates from the cockroach, Diploptera punctata. The apparent K_M for the conversion of acetyl-CoA to HMG-CoA was 200 μM. The enzyme activity was measured during a cycle of JH synthesis in adult mated females. HMG-CoA synthase followed the pattern of juvenile hormone III synthesis closely with a peak on day 5 (1.89 ± 0.07 nmol/h/pair-eq.), and the decline of its activity occurred earlier than that of HMG-CoA reductase.

Two carboxylesterases (TE-I and TE-II) from the mid-gut of the termite Odentotermes horni. W., have been purified to apparent homogeneity by means of ammonium sulfate fractionation, gel-permeation on Sephadex G-75 and Ultragel AcA-34 and ion-exchange chromatography on DEAE-Sephacel. The homogeneity of the preparations was confirmed by polyacrylamide gel electrophoresis (PAGE), gel-electrofocussing and Ouchterlony double immunodiffusion. The apparent molecular weights determined by gel-permeation on Sephadex G-200 was 78,350 and by SDS-PAGE 78,500. In the presence of 2-mercaptoethanol, the proteins were split into two subunits of equal size with subunit molecular weight of about 40,000. The enzymes were found to have a Stokes radius of 3.35 nm. The amino acid analysis of the purified enzymes revealed the presence of a greater number of acidic and neutral amino acids than in other insect carboxylesterases. The isoelectric points of the enzymes, TE-I and TE-II, were 5.4 and 5.6, respectively. The two enzymes were inhibited by organophosphates. The substrate preference and inhibition patterns classify these enzymes as carboxylesterases (EC 3.1.1.1), but the physiological function is unknown. The apparent $\text{K}{}_{\mathrm{<mtext>m</mtext>}}$, $\text{V}{}_{\mathrm{<mtext>max</mtext>}}$, $\text{k}{}_{\mathrm{<mtext>i</mtext>}}$ and $\text{I}{}_{50}$ values are listed. The product inhibition studies with the enzymes revealed the linear competitive inhibition with acetate and linear non-competitive inhibition with 1-naphthol. In addition, optimum temperature and pH, thermal stability, effect of temperature and pH on $\text{K}{}_{\mathrm{<mtext>m</mtext>}}$ and $\text{V}{}_{\mathrm{<mtext>max</mtext>}}$ of the two enzymes were determined.

Posterior-midgut homogenate from female stable flies prepared at 12 h after feeding hemolyzed erythrocytes from 6 different mammalian species more readily than homogenate prepared at 22 h. A significant correlation was obtained between the per cent sphingomyelin content of the erythrocyte membrane and the time required for lysis by the 12 h homogenate. Erythrocytes with low sphingomyelin content were more sensitive to lysis than cells with high sphingomyelin. No such correlation exists for hemolysis by 22 h homogenate. Mean corpuscular volume and osmotic fragilities of erythrocytes were not related to hemolysis either by 12 or 22 h homogenate. Determination of phospholipase C and sphingomyelinase activities showed that the hydrolysis rate of phospholipase C in homogenates prepared at 12–14 h was almost twice as much as sphingomyelinase activity. Whereas hydrolysis rates in 22–24 h homogenate were not different and markedly reduced compared to the 12–14 h homogenate. The times required for erythrocyte hemolysis related to the phospholipase C and sphingomyelinase activity profiles suggests that these enzyme activities participate in the in vitro hemolysis of red blood cells. Bovine and human erythrocytes change their biconcave contour into a spiculated spherical shape when they are exposed to midgut homogenate. This shape change is interpreted as a detergent induced modification of the red cell membrane which renders the erythrocytes more vulnerable to hemolysis.

Transcripts of three actin genes accumulate differentially during development of Bombyx mori, indicating distinct patterns of expression for each gene. Two of them are muscle actin encoding genes since one is expressed only in adult muscles which are formed during the late pupal period and the other one is expressed in all the larval as well as adult muscles tested. The third one codes for a cytoplasmic actin present particularly in embryos, larval silk glands and pupae. The structure of the 3′ end of each gene has been determined and indicates the presence of regulation in the choice of polyadenylation sites for the larval and adult muscle actin gene at different developmental stages. The pattern of accumulation of the Bombyx actin transcripts during development has been compared to that of Drosophila actin genes and indicates that three classes of actin genes can be distinguished in these two insect species: adult muscle actin genes, larval and adult muscle actin genes and cytoplasmic actin genes.

Pheromone biosynthesis in female redbanded leafroller moths (RBLR) is under control of a neuropeptide produced in the brain. A bioassay consisting of isolated abdomens was developed to test the mode of action of the pheromone biosynthesis activating neuropetide (PBAN). Pheromone titer and incorporation of radiolabeled acetate into pheromone could be monitored with this bioassay. Synthetic PBAN with sequences identical to PBAN isolated from Heliothis zea and Bombyx mori were active in inducing synthesis of pheromone in RBLR. Removal of the ventral nerve cord in isolated abdomens did not inhibit the action of PBAN. Small amounts of PBAN-like activity was found in hemolymph collected from normal females but not from decapitated females. Severing the VNC in vivo in normal females did not lower the pheromone titer. These data indicate that PBAN is released into the hemolymph and then travels to its site of action. A two-fold increase in both pheromone titer and radiolabeled acetate incorporation upon incubation with PBAN was shown with isolated pheromone glands. However, the differences between control and PBAN-induced values were smaller than those obtained with the isolated abdomen culture bioassay where a seven-fold increase was observed. A decrease in pheromone titer was seen upon the in vivo removal of the corpus bursae from normal females. Removal of the corpus bursae in the isolated abdomen cultures also abolished the activity of PBAN. However, cutting the cervix bursae and leaving the corpus bursae in the abdomen culture increased both titer and radiolabeled acetate incorporation into pheromone without the presence of PBAN. An aqueous extract made from the corpus bursae of 5-day-old females was also active by itself in inducing pheromone biosynthesis in the isolated abdomen cultures. Experiments performed using newly emerged females confirmed that the corpus bursae extracts will induce pheromone biosynthesis. These results indicate that both PBAN and the corpus bursae are involved in controlling pheromone biosynthesis in RBLR.

Changes in biliverdin-binding cyanoprotein content in whole body and tissue extracts during development of nymphal and adult (non-diapause) bean bugs, Riptortus clavatus were analyzed by rocket immunoelectrophoresis (RIE). RIE using anti-CPegg serum can be used to determine the content of CP-A (Cp-1, 2 and 3) and CP-B (CP-4) separately. During the nymphal stage CP content of whole body changes cyclically in each instar. In the first nymphal instar, CPegg is the main CP which disappears during the first-second instar ecdysis. In nymphal bugs from the 2nd to 4th instars only CP-B (CP-4) is detected, and at the beginning of each instar the CP content is very low but increases toward the next ecdysis, after which CP decreases and disappears very rapidly. In the 5th nymphal instar, CP-B is the major CP but CP-A (CP-1, 2 and 3) is also detected. These changes in whole body CP content of 5th instar nymphs are observed in both females and males. The content of total CPs in the 5th instar nymph reaches about 1000 μg in the whole insect. During nymphal-adult ecdysis, nymphal CPs decrease and disappear at day 2 after emergence. In female adults CP-A (CP-1 only) increases rapidly after day 4 of adult emergence, while no CP is detected in male adults. In females CPs were detected only in the fat body, hemolymph and ovary. In the mid-5th-instar nymphs, CPs (CP-A and B) are mainly distributed in the hemolymph. CPs in the Hemolymph decrease during nymphal-adult ecdysis, whereas they increase in the fat body. CPs disappear from both the hemolymph and fat body by 2 days after ecdysis. Subsequently in the adult stage only CP-A increases again in the fat body and ovary. By tracer experiments using [³⁵S]-methionine, the fat body was shown to be the site of CP synthesis. CP-A and B synthetic activity was detected in nymphal females whereas, only CP-A synthesis was observed in adult females, while no CP synthesis was seen in adult males.

A 200 kDa protein specifically expressed on the surface of pupal hemocytes of Sarcophaga peregrina was purified from the hemocyte membrane. This protein has been suggested to participate in dissociation of the fat body in the pupal stage of this insect. This protein was found to inhibit the dissociation of the fat body in vitro. Furthermore, it was shown to bind to the fat body and the binding could be saturated. These results suggested that pupal hemocytes expressing the 200 kDa protein interact directly with specific binding sites on the basement membrane of the fat body when they disintegrate this tissue.