The trypsin modulating oostatic factor from the gray fleshfly Neobellieria bullata (Neb-TMOF) is released from the ovary at the end of vitellogenesis and inhibits trypsin biosynthesis in the midgut. This inhibition indirectly results in an arrest of oocyte growth. Additional experiments with N. bullata were performed to characterize its trypsin modulating and oostatic properties in more detail. After suspending the peptide in wheat germ oil, the threshold dose for oostatic activity was lowered one thousand times (2.10(-5) in oil versus 2.10(-2) pmoles per fly in Ringer). By use of the Neobellieria trypsin biosynthesis assay, 17 analogs of the hexapeptide were tested for inhibitory activity. The following structural elements were demonstrated to be critical for biological activity: the alcohol function at position 3 (Thr residue); a positively charged basic group at the C terminus (His residue); and the Asn side chain at positions 1 and 4.
"Oral uptake of corazonin dispersed in water was known to be ineffective in bringing about cuticular melanization. Having the necessity of mixing of corazonin with oil for enhancing its biological activity in mind, as well as the data that dispersion of Neb-TMOF in wheat germ oil lowered the threshold dose for oostatic activity in Neobellieria one thousand times , we wondered whether, perhaps, oral uptake of corazonin dispersed in oil might result in cuticular melanization in albino Locusta migratoria. "
[Show abstract][Hide abstract] ABSTRACT: Upon realizing that for drug delivery in the body, lipidization is a technique used in the pharmaceutical industry, we took in consideration that corazonin melanizes the cuticle of albino Locusta migratoria only when injected in an emulsion in oil, not when applied in a watery solution. In this study, we investigate the possibility for oral uptake of corazonin dispersed in oil, and validated the activity by a melanization assay. Not only was it active, it also induced red cuticular coloration in some animals, and it was also unexpectedly lethal for nymphs, but not for adults. These results necessitate the revision of the potential of (some) peptides for insect control. Also, they suggest practical recommendations for the application of other peptides in physiological assays where oil could be used as a simple slow release formula.
"During the last decade, the number of studies of insect peptides and their analogues have significantly increased (Menn et al., 1991; Janssen et al., 1998). A special attention has been paid to the decapeptide H– Tyr–Asp–Pro–Ala–Pro–Pro–Pro–Pro–Pro–Pro–OH isolated from the mosquito Aedes aegypti and described by Borovsky et al. (1991,1993,1994) as a trypsin modulating oostatic factor (Aea-TMOF) blocking trypsin synthesis in the midgut of blood-sucking mosquitos and, in this way, preventing protein digestion (Neb-TMFO isolated from Neobellieria bullata has a different structure (Bylemans et al., 1994)). "
[Show abstract][Hide abstract] ABSTRACT: An analogue of insect oostatic peptide, the pentapeptide H-Tyr-Asp-Pro-Ala-Pro-OH (H-YDPAP-OH), was administered to female mice and its effects on reproduction and development of the ovaries were studied. Up to 0.5 mg of the peptide per mice (25 g b.w.) injected intraperitoneally did not change the rate of pregnancy, number of offsprings and histological findings in ovaries and uterus in comparison to saline treated controls.
"Even in this stage, the breakdown is very fast and seemingly puzzling . It should however be noticed that very low concentrations of Neb-TMOF still efficiently inhibit trypsin biosynthesis in Neobellieria (Bylemans et al., 1994; Janssen et al., 1998). At this moment it can not be excluded either that Neb-TMOF itself acts as a precursor for a cleavage product (NPTN or/and LH) that by itself is the most active inhibitor. "
[Show abstract][Hide abstract] ABSTRACT: The unblocked hexapeptidic Trypsin Modulating Oostatic Factor of the fleshfly, an inhibitor of both trypsin and ecdysone biosynthesis, resists very well proteolytic breakdown by enzymes present in the lumen of the gut of previtellogenic fleshflies. However, when incubated in hemolymph of adult flies, females and males, its half-life time is a mere 0.5 min. In hemolymph of last instar larvae, this value increases to about 1.5 min. Whereas PMSF, a potent inhibitor of serine proteases has no effect, captopril and lisinopril, both known to be specific inhibitors of mammalian angiotensin I converting enzyme (ACE), effectively inhibit TMOF breakdown in fly hemolymph. Digestion of Neb-TMOF by recombinant Drosophila AnCE on itself results in identical degradation products as with total hemolymph. In both cases ESI-Qq-oa-Tof mass spectrometry demonstrated the appearance of peptide fragments with the sequences NPTN, LH and NP. These observations not only confirm the reported presence of circulating ACE-like activity in flies but also strongly suggest that in flies this hemolymph ACE-like activity might be involved in the regulation of the oostatic activity as exerted by Neb-TMOF.
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