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PubMed2001

Trypsin cleavage stabilizes the rotavirus VP4 spike.

Trypsin enhances rotavirus infectivity by an unknown mechanism. To examine the structural basis of trypsin-enhanced infectivity in rotaviruses, SA11 4F triple-layered particles (TLPs) grown in the absence (nontrypsinized rotavirus [NTR]) or presence (trypsinized rotavirus [TR]) of trypsin were characterized to determine the structure, the protein composition, and the infectivity of the particles before and after trypsin treatment. As expected, VP4 was not cleaved in NTR particles and was cleaved into VP5(*) and VP8(*) in TR particles. However, surprisingly, while the VP4 spikes were clearly visible and well ordered in the electron cryomicroscopy reconstructions of TR TLPs, they were totally absent in the reconstructions of NTR TLPs. Biochemical analysis with radiolabeled particles indicated that the stoichiometry of the VP4 in NTR particles was the same as that in TR particles and that the VP8(*) portion of NTR, but not TR, particles is susceptible to further proteolysis by trypsin. Taken together, these structural and biochemical data show that the VP4 spikes in the NTR TLPs are icosahedrally disordered and that they are conformationally different. Structural studies on the NTR TLPs after trypsin treatment showed that spike structure could be partially recovered. Following additional trypsin treatment, infectivity was enhanced for both NTR and TR particles, but the infectivity of NTR remained 2 logs lower than that of TR particles. Increased infectivity in these particles corresponded to additional cleavages in VP5(*), at amino acids 259, 583, and putatively 467, which are conserved in all P serotypes of human and animal group A rotaviruses and also corresponded with a structural change in VP7. These biochemical and structural results show that trypsin cleavage imparts order to VP4 spikes on de novo synthesized virus particles, and these ordered spikes make virus entry into cells more efficient.

Amino Acid Sequence↗
PubMed1979

Molecular forms of immunoreactive pancreatic cationic trypsin in pancreatitis patient sera.

The molecular forms of immunoreactive pancreatic cationic trypsin in sera of patients with acute pancreatic inflammation have been characterized using a radioimmunoassay technique that is capable of detecting trypsinogen as well as trypsin bound to alpha 1-antitrypsin. Trypsin bound to alpha 2-macroglobulin is not immunoreactive under normal assay conditions. However, alpha 2-macroglobulin-bound trypsin can be detected after gel filtration of serum on Bio-Gel A-0.5 m and acid treatment of column fractions. The average serum level of immunoreactive cationic trypsin from 20 patients with acute pancreatic inflammation was 1,590 ng/ml. An average normal value of 26 ng/ml has been obtained previously. Serum samples from 14 patients with pancreatic inflammation were chromatographed under conditions that resolve trypsinogen, alpha 1-antitrypsin-bound trypsin, and alpha 2-macroglobulin-bound trypsin. In each case, the major portion of the immunoreactive material eluted at a position corresponding to free trypsinogen, while a minor fraction of the immunoreactive material appeared to be trypsin bound to alpha 1-antitrypsin. The zymogen nature of the major peak was confirmed in one case by activation with human enteropeptidase. In 11 of 14 patients, acid treatment of the alpha 2-macroglobulin peak yielded immunoreactive trypsin.

Cations↗
PubMed2004

Pancreatic trypsin cleaves intestinal alkaline sphingomyelinase from mucosa and enhances the sphingomyelinase activity.

Sphingomyelin (SM) hydrolysis in the gut has implications in colonic tumorigenesis and cholesterol absorption. It is triggered by intestinal alkaline sphingomyelinase (Alk-SMase) that is present in the intestinal mucosa and content. The mechanism by which the enzyme is released into the lumen is not clear. We studied whether trypsin can dissociate Alk-SMase from the mucosa and affect its activity. During luminal perfusion of rat intestine, addition of trypsin to the buffer increased Alk-SMase activity in the perfusate output by about threefold. Treating COS-7 cells transfected with Alk-SMase cDNA with trypsin increased the SMase activity in the medium and reduced that in the cell lysate dose dependently. The appearance of Alk-SMase in the perfusate and culture medium was confirmed by Western blot analysis. The effect of trypsin was blocked by trypsin inhibitor, and neither chymotrypsin nor elastase had a similar effect. We also expressed the full length and COOH-terminal truncated Alk-SMase in COS-7 cells and found that the activity of the full-length enzyme is mainly in the cells, whereas that of the truncated form is mainly in the medium. Both forms were active, but only the activity of the full-length Alk-SMase was enhanced by trypsin. By linking a poly-His tag to the constructed cDNA, we found that the first tryptic site Arg440 upstream of the signal anchor was attacked by trypsin. In conclusion, trypsin cleaves the Alk-SMase at the COOH terminal, releases it from mucosa, and meanwhile enhances its activity. The findings indicate a physiological role of trypsin in SM digestion.

Alkalies↗
PubMed1984

Intestinal uptake of trypsin in newborn and weaned rabbits.

Earlier studies have shown that the uptake of intact proteins from the intestinal lumen into the systemic circulation is increased in neonates. The present experiments tested the uptake of trypsin in newborn compared with 4-wk-old weaned rabbits. Trypsin (200 mg/100 g body wt) was administered by gavage to newborn and 4-wk-old rabbits. Four hours later, the tryptic activity and immunoreactive trypsin (i-trypsin) content of serum from newborn rabbits exceeded that of the older animals. After Sephadex G-200 gel filtration of serum from animals gavaged with trypsin, tryptic activity was detected in the excluded volume (presumably reflecting trypsin bound to alpha 2-macroglobulin), and i-trypsin was detected in the included volume (presumably reflecting trypsin bound to alpha 1-antitrypsin). In vitro experiments demonstrated that large amounts of trypsin were required to overwhelm the antiprotease present in normal rabbit serum. We suggest that complete or partial deficiencies of serum protease inhibitors may permit proteases taken up from the intestinal lumen of the neonate to circulate, reach the liver, and induce tissue injury at this site.

Animals↗
PubMed1996

Effects of urinary trypsin inhibitor on myometrial contraction in term and preterm deliveries.

The aim of this research was to study the concentration of urinary trypsin inhibitor in amniotic fluid (AF) and its effect on myometrial contraction in term and preterm deliveries. Urinary trypsin inhibitor was measured in AF of term and preterm labor. Immunohistochemical staining of amnion and myometrium was carried out. Isometric uterine contraction was studied to elucidate the effect of AF and urinary trypsin inhibitor on the contractile activity of term and preterm myometrium. The effect of urinary trypsin inhibitor on the production of prostaglandin E2 (PGE2) from myometrial cultures stimulated by IL-8, IL-1 and LPS was verified. Urinary trypsin inhibitor was significantly increased in AF of cases of preterm delivery (p < 0.0001). Amnion and myometrium of preterm deliveries were faintly stained for urinary trypsin inhibitor compared to term delivery. Amniotic fluid and urinary trypsin inhibitor could successfully inhibit-myometrial contraction. Also, urinary trypsin inhibitor could significantly inhibit the production of PGE2 in the myometrial cell cultures stimulated by IL-1 and LPS (p < 0.001 and 0.0005). IL-8 has no significant effect on PGE2 production from myometrial cell culture. Urinary trypsin inhibitor suppresses myometrial contraction in term and preterm deliveries. It may play a role in maintaining normal pregnancy and preventing preterm delivery.

Amnion↗
PubMed1982

Studies on trypsin activation of inactive renin in rat plasma.

The experimental conditions of trypsin activation of inactive renin in rat plasma have been studied. Our results showed that the pH optimum of trypsin-activated renin is 6.2, the same as that of rat plasma active renin. Trypsin concentration and incubation time might also interfere with the activation process. Trypsin concentration below 2 mg/ml cannot activate inactive renin. Trypsin at a concentration of 6 mg/ml for 1 min. can cleave dialyzable fragments from renin substrate which can generate Angiotensin I at 37 degrees C with a pH optimum of 5.3 but which do not affect Angiotensin generation at pH 6.2. Longer incubations (more than 2 min.), on the contrary, can produce a cleavage at 4 degrees C of Angiotensin I containing fragments directly from renin substrate strongly interfering with measurements of renin activity at pH 6.2. Trypsin concentrations lower than endogenous rat plasma anti-trypsin activity do not activate inactive renin. Much higher concentrations of trypsin, however, are needed to obtain optimum activation of inactive renin. In average, 40% of the total circulating renin in rat plasma can be activated by trypsin.

Animals↗
PubMed1995

Concentrations of trypsin inhibitor and immunoglobulins in colostrum of Jersey cows.

Colostrum samples from 49 Jersey cows were analyzed for concentrations of trypsin inhibitor, IgG, IgM, IgA, TS, fat, specific gravity, and N fractions. Colostrum (100 ml) was sampled from each cow as soon as possible after parturition. Mean concentrations of IgG, IgM, and IgA were 84.6, 3.4, and 4.5 g/L, respectively. Mean concentration of trypsin inhibitor was 56 mg of trypsin inhibited/dl of colostrum. Concentration of trypsin inhibitor was unaffected by lactation number and averaged 60, 53, and 54 mg of trypsin inhibited/dl of colostrum for cows in first, second, and third or later lactations, respectively. Colostral trypsin inhibitor and IgG were correlated (.54), although correlations between trypsin inhibitor and IgM and IgA were not significant. Trypsin inhibitor in colostrum was also positively correlated with fat, total N, protein N, noncasein N, and TS in colostrum. Variation in concentration of trypsin inhibitor from first-milking colostrum was closely related to colostral IgG concentration and may serve to protect IgG and other proteins from proteolytic degradation in the intestine of the neonatal calf.

Animals↗
PubMed2001

The ratio of trypsin-2-alpha(1)-antitrypsin to trypsinogen-1 discriminates biliary and alcohol-induced acute pancreatitis.

BACKGROUND: Rapid determination of the etiology of acute pancreatitis (AP) enables institution of appropriate treatment. We evaluated the ability of trypsinogen-1, trypsinogen-2, trypsin-1-alpha(1)-antitrypsin (AAT), and trypsin-2-AAT in serum to identify the etiology of AP. METHODS: The study consisted of 67 consecutive patients with AP admitted to Helsinki University Central Hospital. Forty-two had alcohol-induced AP, 16 had biliary AP, and 9 had unexplained etiology. Serum samples were drawn within 12 h after admission. Trypsinogen-1, trypsinogen-2, trypsin-1-AAT, and trypsin-2-AAT were determined by time-resolved immunofluorometric assays. Logistic regression was used to estimate the ability of the serum analytes to discriminate between alcohol-induced and biliary AP. The validity of the tests was evaluated by ROC curve analysis. RESULTS: Patients with alcohol-induced AP had higher median values of trypsin-1-AAT (P = 0.065), trypsinogen-2 (P = 0.034), and trypsin-2-AAT (P <0.001) than those with biliary AP, who had higher values of amylase (P = 0.002), lipase (P = 0.012), and alanine aminotransferase (P = 0.036). The ratios of trypsin-2-AAT to trypsinogen-1, lipase, or amylase efficiently discriminated between biliary and alcohol-induced AP (areas under ROC curves, 0.92-0.96). CONCLUSIONS: Trypsinogen-2 and trypsin-2-AAT are markedly increased in AP of all etiologies, whereas trypsinogen-1 is increased preferentially in biliary AP. The trypsin-2-AAT/trypsinogen-1 ratio is a promising new marker for discrimination between biliary and alcohol-induced AP.

Acute Disease↗
PubMedDate not supplied

Experimental studies on curing elapid bite with trypsin.

The local injection of trypsin can be regarded as a new and effective therapy for venomous snakebite. Our experiments indicate that when mice or dogs have been injected with the lethal dose of elapid venom subcutaneously, they can all survive and have no symptoms of systemic poisoning if necessary dose of trypsin is injected locally and promptly. When the lethal dose of cobra venom is injected into mice, all of them can survive if trypsin is given within 15 minutes. And even if trypsin is given 20--50 minutes later, 50--90% of the mice can avoid death. The prompt local injection of trypsin is found effective to cure elapid bite as well as antivenins and is a very "broad spectrum' therapy having no specificity. There are no severe side-effects when trypsin is injected locally. The production of trypsin is rather simple and its preservation needs no special conditions. Trypsin can be put into pocketable first-aid auto-injector and can be used after snakebite at the possible earlier time. Even though a rather long time has elapsed after snakebite, the local injection of trypsin is still useful to destroy the large amount of venom stored in the tissues of the bitten area.

Animals↗
PubMed1975

Study on mammalian ribosomal protein reactivity in situ. III. Effect of trypsin on 40S and 60S subunits.

Rat liver 40S and 60S ribosomal subunits were treated with increasing concentrations of trypsin. The activity of both trypsin-treated subunits, when assayed for polyphenylalanine synthesis, progressively decreased, but the 60S subunits were inactivated at much lower trypsin concentrations than were the 40S ones. The sedimentation coefficients of trypsin-treated subunits were identical to those of control subunits when sucrose gradients containing 0.5 M KCl were used. When the sucrose gradients were prepared with a low salt buffer (80 mM KCl), dimer formation was observed with control subunits, but not with trypsin-treated ones. Two-dimensional gel electrophoresis analysis of the proteins extracted from trypsin-treated subunits revealed that all ribosomal proteins in the subunits were accessible to the enzyme. However, several proteins were more resistant to trypsin in compact subunits than when they were free or in unfolded subunits. Proteins of the 60S subunits were generally digested by lower trypsin concentrations than those of the 40S subunits. From the quantitative measurements of the undigested proteins, a classification of the proteins from both subunits according to their trypsin sensitivity was established. These results were compared with those previously obtained concerning ribosomal protein reactivity to chemical reagents.

Animals↗
PubMed1976

Abolishment of oral trypsin inhibitor stimulation of the rat exocrine pancreas after duodeno-jejunal resection.

The effect of long-term oral trypsin inhibitor administration on the exocrine pancreas was studied in unoperated rats and in rats operated on by a 30% proximal small intestinal resection. The following observations were made: in unoperated rats sacrificed 18 hours after the last trypsin inhibitor ingestion there was an increase of the wet weight of pancreas, increase of the pancreatic protein, and an increase of pancreatic and intestinal trypsin(ogen) and of pancreatic amylase by comparison with the controls. In operated rats, treated and examined in an identical way, no influences on the exocrine pancreas were found. It is suggested that the abolishment of the trypsin inhibitor effects on the exocrine pancreas in operated rats reflects the removal of the site of production of one or more intestinal hormone(s) or factor(s) responsible for these effects. In unoperated rats examined 4 hours after the last trypsin inhibitor ingestion a reduction of the pancreatic trypsinogen and amylase and an increase of the intestinal amylase were found, indicating a secretory response of the pancreas to the intraluminal trypsin inhibitor; the low values of intestinal trypsin found in these rats probably reflect inhibition of rat trypsin by the bovine lung trypsin inhibitor.

Administration, Oral↗
PubMed1991

Immunohistochemical demonstration of pancreatic alpha-amylase and trypsin in intrahepatic bile ducts and peribiliary glands.

Epithelia of intrahepatic bile ducts and peribiliary glands were immunohistochemically examined for pancreatic alpha-amylase and trypsin in 54 normal autopsied livers. alpha-Amylase was evaluated with a polyclonal antibody, and trypsin was assayed with both polyclonal and monoclonal antibodies. alpha-Amylase was observed in large ducts, septal ducts and peribiliary glands in most livers and was seen in interlobular ducts in seven (13%) livers. Trypsin immunoreactivity with the polyclonal antibody was observed in peribiliary glands in 21 (39%) livers; it was absent in intrahepatic bile ducts in all but one liver. Trypsin immunoreactivity with the monoclonal antibody was present in large ducts, septal ducts and peribiliary glands in about 70% of the livers and was seen in interlobular ducts in two (4%) livers. Bile ductules were always negative for the two antigens. Some epithelia of peribiliary glands positive for both alpha-amylase and trypsin histologically resembled pancreatic acinar cells. alpha-Amylase and trypsin immunoreactivities of intrahepatic biliary epithelia and pancreatic aninar cells were eliminated by absorption of primary antibodies by alpha-amylase or trypsin, suggesting the specificities of the immunoreactivities. These data suggest that epithelia of intrahepatic large ducts, septal ducts and peribiliary glands contain pancreatic alpha-amylase in most livers and that they contain trypsin in about 70% of livers. alpha-Amylase and trypsin may be secreted into intrahepatic bile duct lumens, thereby exerting important effects on the physiology of the intrahepatic biliary tree and hepatic bile.

Adult↗
PubMed1976

Regulation of glycogen synthetase. Effects of trypsin on the structure, activity, and phosphorylation of the skeletal muscle enzyme.

Incubation of purified skeletal muscle glycogen synthetase I with trypsin (10 mug/ml) for 15 min decreased the Stokes radius of the enzyme from 68 A to 62 A and the subunit molecular weight from 90,000 to about 73,000. No decrease in the sedimentation coefficient of 13.3 S could be detected. It was calculated that native synthetase I is a tetramer of molecular weight 360,000 to 370,000. Trypsin also catalyzed a decrease in the synthetase activity ratio (minus glucose-6-P to plus glucose-6-P) largely by reducing minus glucose-6-P activity. The magnitude of the trypsin effect on the synthetase activity ratio was very similar to that produced by phosphorylation of synthetase by the cyclic AMP-dependent protein kinase. The activity ratio could be lowered from that characteristic of synthetase I, 0.85, to 0.25 either by trypsin digestion or by incorporation of 1 mol of Pi per mol of synthetase subunit. An activity ratio of less than 0.05 could be obtained in three ways as follows, (a) phosphorylation to 2 Pi/subunit, (b) phosphorylation to 1 Pi/subunit (ratio=0.25) followed by trypsin treatment, (c) trypsin treatment (ratio=0.25) followed by phosphorylation. When trypsinized synthetase was phosphorylated by the catalytic subunit of cyclic AMP-dependent protein kinase, 1 Pi/subunit was incorporated. Trypsin (6 mug/ml) led to a rapid release of about 50% of the radioactivity from 32P-synthetase regardless of whether the enzyme contained 1 or 2 phosphates per subunit. It was concluded that two sites on the enzyme subunit are highly susceptible to phosphorylation catalyzed by the cyclic AMP-dependent protein kinase. The data indicate that the 1st mol of Pi incorporated is distributed about equally between the two sites. A model is proposed to account for these observations. The data further indicate that a peptide containing one site is removed by trypsin. This reduces enzyme activity to the same extent as does phosphorylation of the site in the intact protein.

Animals↗
PubMed2000

Crystal structure of cancer chemopreventive Bowman-Birk inhibitor in ternary complex with bovine trypsin at 2.3 A resolution. Structural basis of Janus-faced serine protease inhibitor specificity.

Understanding molecular recognition on a structural basis is an objective with broad academic and applied significance. In the complexes of serine proteases and their proteinaceous inhibitors, recognition is governed mainly by residue P1 in accord with primary serine protease specificity. The bifunctional soybean Bowman-Birk inhibitor (sBBI) should, therefore, interact at LysI16 (subdomain 1) with trypsin and at LeuI43 (subdomain 2) with chymotrypsin. In contrast with this prediction, a 2:1 assembly with trypsin was observed in solution and in the crystal structure of sBBI in complex with trypsin, determined at 2.3 A resolution by molecular replacement. Strikingly, P1LeuI43 of sBBI was fully embedded into the S(1) pocket of trypsin in contrast to primary specificity. The triple-stranded beta-hairpin unique to the BBI-family and the surface loops surrounding the active site of the enzyme formed a protein-protein-interface far extended beyond the primary contact region. Polar residues, hydrophilic bridges and weak hydrophobic contacts were predominant in subdomain 1, interacting specifically with trypsin. However, close hydrophobic contacts across the interface were characteristic of subdomain 2 reacting with both trypsin and chymotrypsin. A Met27Ile replacement shifted the ratio with trypsin to the predicted 1:1 ratio. Thus, the buried salt-bridge responsible for trypsin specificity was stabilised in a polar, and destabilized in a hydrophobic, environment. This may be used for adjusting the specificity of protease inhibitors for applications such as insecticides and cancer chemopreventive agents.

Amino Acid Sequence↗
PubMed1982

Isolation and partial characterization of the pancreatic secretory trypsin inhibitor in the rat.

Isolation in a 55% yield of the low molecular weight pancreatic secretory trypsin inhibitor was achieved by gel filtration of an acid extract of whole inactive rat pancreas juice on Sephadex G-50 at pH 2.5 followed by desalting and ion-exchange chromatography on SP Sephadex C-50 at pH 4.5. Two distinct chromatographic fractions were obtained, labeled fraction 1 and 2. Fractions 1 and 2 showed three, respectively two, distinct closely migrating cationic bands on gel electrophoresis in barbital buffer, pH 8.6. Each fraction demonstrated one band on polyacrylamide disc electrophoresis at pH 4.6. The inhibitor is homogenous on gel filtration and on the basis of its stoichiometry with active site titrated rat anionic trypsin. Its molecular weight is approx. 6024. The amino acid composition is included. Rat pancreatic secretory trypsin inhibitor is trypsin-specific and interacts on a 1:1 molar basis with rat trypsin. It is a good inhibitor of bovine trypsin but a poor inhibitor of human cationic trypsin and its binding to trypsin is reversible by acidification. Like other inhibitors of this sort, it is present in about 0.1-0.2% of the total protein content of the juice, and normally exists in its free form. A simple procedure for the production of antiserum to the inhibitor which is a poor antigen is also described.

Amino Acids↗
PubMed1979

Kunitz-type proteinase inhibitors derived by limited proteolysis of the inter-alpha-trypsin inhibitor, I. Determination of the amino acid sequence of the antitryptic domain by solid-phase Edman degradation.

The acid-stable trypsin inhibitor of human serum and urine is released in vivo by limited proteolysis from the high molecular weight, acid-labile inter-alpha-trypsin inhibitor. When complexed with trypsin, both this acid-stable, active derivative and the inter-alpha-trypsin inhibitor can be degraded in vitro by prolonged digestion with trypsin to a low molecular weight "minimal" inhibitor. This minimal trypsin inhibitor was sequenced and found to be homologous to the known Kunitz-type inhibitors (e.g. the basic trypsin-kallikrein inhibitor from bovine organs). This indicates that the antitryptic activity of the big inter-alpha-trypsin inhibitor is due to a Kunitz-type domain.

Alpha-Globulins↗
PubMed1999

Urinary trypsin inhibitor levels in amniotic fluid of normal human pregnancy: decreased levels observed at parturition.

OBJECTIVE: Urinary trypsin inhibitor, a light chain of inter-alpha-trypsin inhibitor, is reported to inhibit uterine contractility during pregnancy. The objective was to measure amniotic fluid urinary trypsin inhibitor levels in women throughout pregnancy. STUDY DESIGN: We determined levels of urinary trypsin inhibitor in human amniotic fluid (n = 40) by means of Western blot analysis. For quantification, computerized scanning and densitometry were used. Results were analyzed for statistical significance with the Mann-Whitney U test. RESULTS: During pregnancy, mean amniotic fluid urinary trypsin inhibitor levels (+/-SD) were 1.5 +/- 0.22, 1. 2 +/- 0.18, and 0.58 +/- 0.24 micromol/L at 15 to 22 (n = 10), 30 to 35 (n = 5), and 37 to 40 (n = 10) weeks' gestation, respectively. There was a significant negative correlation of urinary trypsin inhibitor level with gestational age. A significant difference was observed in amniotic fluid urinary trypsin inhibitor levels before and after (0.10 +/- 0.03 micromol/L; n = 15) the onset of labor. CONCLUSION: Amniotic fluid urinary trypsin inhibitor levels decrease significantly at term. These results support the hypothesis that parturition may occur through the down-regulation of urinary trypsin inhibitor, which may decrease uterine contractility and maintain the uterus in a state of quiescence during pregnancy.

Amniotic Fluid↗
PubMed1999

Nature of the anchors of membrane-bound aminopeptidase, amylase, and trypsin and secretory mechanisms in Spodoptera frugiperda (Lepidoptera) midgut cells.

Spodoptera frugiperda larvae have a microvillar aminopeptidase and both soluble and membrane-bound forms of amylase and trypsin. Membrane-bound aminopeptidase is solubilized by glycosyl phosphatidylinositol-specific phospholipase C (GPI-PLC) and detergents, suggesting it has a GPI anchor. Membrane-bound trypsin is not affected by GPI-PLC, although it is solubilized by papain and by different detergents. Membrane-bound amylase is similar to trypsin, although once solubilized in detergent it behaves as a hydrophilic protein. Musca domestica trypsin antiserum cross-reacts with only one polypeptide from S. frugiperda midgut. With this antiserum, trypsin was immunolocalized in the anterior midgut cells at the microvillar surface and on the membranes of secretory vesicles found in the apical cytoplasm and inside the microvilli. The data suggest that in this region trypsin is bound to the secretory vesicle membrane by a hydrophobic anchor. Vesicles migrate through the microvilli and are discharged into the lumen by a pinching-off process. Trypsin is then partly processed to a soluble form and partly, still bound to vesicle membranes, incorporated into the peritrophic membrane. In posterior midgut cells, trypsin immunolabelling is randomly distributed inside the secretory vesicles and at the microvilli surface, suggesting exocytosis. Amylase probably follows a route similar to that described for trypsin in anterior midgut, although membrane-bound forms (peptide anchor) solubilize apparently as a consequence of a pH increase inside the vesicles.

Journal Article↗