Trypsin Biosynthesis Research Articles

Characterization and localization of mosquito-gut receptors for trypsin modulating oostatic factor using a complementary peptide and immunocytochemistry.

The gut receptor of trypsin-modulating oostatic factor (TMOF), a decapeptide hormone that regulates trypsin biosynthesis in the mosquito gut, has been characterized. The binding of TMOF to mosquito gut membranes reached maximum at pH 7.4 and 24 degrees C. No binding was observed at pH 2.5 and the binding to the membranes declined rapidly at pH 8.0. At equilibrium, maximum binding to the receptor was observed at 60 min and 24 degrees C. A synthetic complementary decapeptide NH2-Ile-Leu-Gly-Arg-Gly-Gly-Gly-Gly-Gly-Gly-COOH (FOMT) for TMOF successfully competed with the gut receptor, and specifically bound TMOF (Kd = 4 microM and Kassoc = 2.5 x 10(5) M-1). TMOF binding to gut membranes was characterized with FOMT and a specific ELISA to the hormone at 24 and 72 h after blood feeding. Two classes of binding sites were found on the gut membrane; high affinity (Kd1 = 4.6 +/- 0.7 x 10(-7) M; Kassoc = 2.2 x 10(6) M-1 Bmax = 0.1 pmol/gut) and low affinity (Kd2 = 4.43 +/- 1 x 10(-6) M; Kassoc = 2.3 x 10(5) M-1; Bmax = 0.2 pmol/gut). The total binding sites for high and low affinity classes of TMOF per gut were estimated as 6.3 x 10(10) and 1.1 x 10(11) sites, respectively. Specific binding sites on the gut increased after the blood meal and were visualized by immunocytochemical staining. These results suggest that TMOF regulates trypsin biosynthesis by binding to specific receptor sites that are located on the mosquito gut, and that this receptor can be studied using a complementary peptide approach.

Biosynthesis, secretion, and immunocytochemistry of trypsin modulating oostatic factor of Aedes aegypti

AbstractTrypsin modulating oostatic factor (TMOF) was followed by RIA in the ovary of female Aedes aegypti before and after the blood meal. The amount of TMOF in a pair of ovaries from females fed sugar for 3 days or blood for 24 h was low (1.7 ng). Between 24 and 48 h after the blood meal the amount of TMOF in the ovaries rapidly increased and reached a peak of 104 ng at 48 h. The amount of TMOF in the head of a female A. aegypti was very low (0.05 to 0.1 ng) during sugar and blood feeding. Immunocytochemical methodology identified the follicular epithelium as the site of biosynthesis of TMOF in the ovary. Females ovariectomized and fed a blood meal continued to synthesize trypsin for 64 h, whereas intact controls stopped at 40 h, indicating that a factor from the ovary regulates trypsin biosynthesis. Ovaries incubated in vitro with [3H]proline synthesized [pro‐3H]TMOF that was identified by HPLC and by anti‐TMOF serum. The ovary started to synthesize TMOF in vitro 24 h after the blood meal, and the synthesis reached a peak at 36 h and then declined. The synthesis of TMOF by the ovary is closely correlated with the termination of trypsin biosynthesis in the female mosquito's midgut. Ovaries that were pulsed with [3H]proline for 30 min synthesized [pro‐3H]TMOF which was chased into the medium with unlabeled proline, indicating that the hormone is secreted by the ovary. These results indicate that TMOF is a secretory peptide, synthesized by the ovarian follicular epithelium and that it modulates trypsin biosynthesis in the mosquito's gut. © 1994 Wiley‐Liss, Inc.

Mass spectrometry and characterization of Aedes aegypti trypsin modulating oostatic factor (TMOF) and its analogs

Trypsin modulating oostatic factor (TMOF), a decapeptide that directly inhibits the biosynthesis of trypsin- and chymotrypsin-like enzymes in epithelial cells of mosquito midgut and indirectly inhibits vitellogenesis in anautogenous females, has been sequenced by Fourier transform mass spectrometry analysis. The peptide has a primary amino acid sequence of NH 2-Tyr-Asp-Pro-Ala-(Pro) 6-COOH and probably exhibits left-handed helical conformation as was shown by computer stereoview simulation. The factor is metabolized very rapidly (half-life of 1.6 h) in intact mosquitoes when injected after the blood meal. Inhibition of trypsin biosynthesis was followed in ligated abdomens, which synthesize trypsin but do not metabolize TMOF. At concentrations of 3 × 10 −9 M and 6.8 × 10 −6 M, TMOF inhibited 50 and 90% of trypsin-like enzyme biosynthesis, respectively. Several analogs of varying chain lengths were synthesized and evaluated for biological activity using dose-response curves. Switching the positions of Tyr and Asp at the N-terminus reduced the activity of the hormone, indicating that the N-terminus is important for biological activity. Removal of two to five prolines at the C-terminus also reduced activity, indicating that both the N- and C-termini are important. Synthesis of trypsin-like isozyme was followed in several insect species using [1,3- 3H]diisopropyl-fluorophosphate (DFP) in the presence of tosylamide-2-phenylethyl chloromethyl ketone. Marked reduction of [1,3- 3H]diisopropyl-phosphoryl-trypsin-like derivatives was noted after TMOF treatment, as assessed by polyacrylamide gel electrophoresis. These results indicate that the biosynthesis of trypsin-like enzyme in mosquitoes and other insects may be regulated by sequence-related TMOFs.

Regulation by a protein-free carbohydrate-rich diet of rat pancreatic mRNAs encoding trypsin and elastase isoenzymes

The levels of mRNAs coding for trypsin and elastase isoenzymic forms were determined in the pancreatic tissue of rats fed a high-carbohydrate protein-free diet for a 0-5-day period. No change in the amounts of mRNAs coding for the two isoelastases was observed, although previous results showed that the biosynthesis of anionic elastase was markedly increased, whereas the biosynthesis of cationic elastase decreased, suggesting the existence of a translational-control mechanism in response to nutritional substrates. In contrast, the levels of mRNAs specific for the three isotrypsins were significantly enhanced, possibly as a result of transcriptional regulation and/or a change in messenger stability. In combination with earlier observations of an overall decrease in cationic trypsin biosynthesis during the same nutritional manipulation, these results suggest that formation of this enzyme is also subject to translational control.