Optimisation of conditions for the affinity chromatography of human enterokinase on immobilised p-aminobenzamidine. Improvement of the preparative procedure by inclusion of negative affinity chromatography with glycylglycyl-aniline

The Global Status and Trends of Enteropeptidase: A Bibliometric Study

Background

Enteropeptidase (EP) is a type II transmembrane serine protease and a physiological activator of trypsinogen. Extensive studies related to EP have been conducted to date. However, no bibliometric analysis has systematically investigated this theme. Our study aimed to visualize the current landscape and frontier trends of scientific achievements on EP, provide an overview of the past 120 years and insights for researchers and clinicians to facilitate future collaborative research and clinical intervention.

Methods

Quantitative analysis of publications relating to EP from 1900 to 2020 was interpreted and graphed through the Science Citation Index Expanded of Web of Science Core Collection (limited to SCIE). Microsoft office 2019, GraphPad Prism 8, VOSviewer, and R-bibliometrix were used to conduct the bibliometric analysis.

Results

From 1900 to 2020, a total of 1,034 publications were retrieved. The USA had the largest number of publications, making the greatest contribution to the topic (n = 260, 25.15%). Active collaborations between countries/regions were also enrolled. Grant and Hermontaylor were perhaps the most impactful researchers in the landscape of EP. Protein Expression and Purification and the Journal of Biological Chemistry were the most prevalent (79/1,034, 7.64%) and cited journals (n = 2,626), respectively. Using the top 15 citations and co-citations achievements clarified the theoretical basis of the EP research field. Important topics mainly include the structure of EP, the affective factors for activating substrates by EP, EP-related disorders, and inhibitors of EP.

Conclusion

Based on the bibliometric analysis, we have gained a comprehensive analysis of the global status and research frontiers of studies investigating EP, which provides some guidance and reference for researchers and clinicians engaged in EP research.

Purification of tropomyosin, paramyosin, actin, tubulin, troponin and kinases for chemiproteomics and its application to different scientific fields

BACKGROUND

p-aminobenzamidine (p-ABA) is used as a ligand in the purification of many serine proteases and in their removal from heterogeneous samples. Moreover, p-ABA has a potent ability to bind Ca(2+)-binding proteins. The binding ability and use of p-ABA in purification processes is still not fully understood.

METHODOLOGY/PRINCIPAL FINDINGS

A p-Aminobenzamidine (p-ABA) ligand enabled the purification of the panallergenic proteins tropomyosin and paramyosin, as well as actin, tubulin, troponin and several kinases and annexins, with variable specificity depending on the tissue source and slight modifications to the purification process. The high affinity of p-ABA to tropomyosin, paramyosin, actin, troponin and myosin is calcium-dependent, since calcium regulates the function of these proteins. In addition, p-ABA probably simulates phosphorylated serine and therefore purified appropriate kinases. Because p-ABA binds to calcium-dependent proteins, and probably those with binding sites containing serine, it is not a suitable inhibitor of proteolysis during the purification of such proteins. p-ABA is widely used to inhibit proteases during protein purification processes, but it is used in columns here to purify non-protease proteins. Two strategies were applied; the first was the inactivation of proteases that were not of interest using protease inhibitors. The second strategy employed was the use of a Ca(2+) wash solution to remove calcium-dependent proteins. The removal of calcium-dependent proteins from rabbit hind muscle pointed out even more selective purification. It is possible to obtain two purified samples: a) calcium dependent proteins and b) calcium independent proteins. Moreover, p-ABA may be useful as a model to study processes involving the phosphorylation of serine.

CONCLUSION

A p-Aminobenzamidine (p-ABA) ligand enabled the purification of non-protease proteins, with variable specificity depending on the tissue source and slight modifications to the purification process. The method is applicable to various scientific branches, but is especially practical for medicinal applications.

Aminopeptidases and proteolipids of intestinal brush border

The presence of human blood group A determinants has been shown on the A+ rabbit intestinal brush border glycoproteins, particularly hydrolases. Sugar compositions of aminopeptidases N from A+ and A- rabbits were compatible with the presence in these molecules of eight N-linked glycans and of two O-linked glycans bearing the A determinants in A+ animals. The exact relative molecular masses of hydrophobic domain(s) of aminopeptidases N and A from pig and rabbit intestinal brush border have been determined by an isotopic dilution technique. The values obtained were compatible with the anchorage in the membrane of the monomeric rabbit enzymes, or of each subunit of the dimeric pig enzymes, by their N-terminal sequences, composed of 20-25 hydrophobic amino acids. This N-terminal hydrophobic sequence (14 residues) has been determined for rabbit aminopeptidase N. Short peptides containing approximately 60% hydrophobic amino acids have been extracted by chloroform-methanol from purified brush border and basolateral membranes of pig enterocytes. Their molecular properties were very similar to those of the aminopeptidase anchors released by trypsin treatment of detergent-extracted enzymes. However, several lines of evidence failed to support the assumption that these free hydrophobic peptides can be identified with anchors left inside the bilayer after proteolytic cleavage of surface hydrolases.

Biochemical and molecular modeling analysis of the ability of two p-aminobenzamidine-based sorbents to selectively purify serine proteases (fibrinogenases) from snake venoms

Snake venoms contain several trypsin-like enzymes with equivalent physicochemical characteristics and similar inhibition profiles. These are rather difficult to separate by classical purification procedures and therefore constitute a good model for affinity chromatography analysis. Some of these trypsin homologues present fibrinogenase activity, mimicking one or more features of the central mammalian coagulation enzyme, thrombin. It was previously demonstrated that a number of amidine derivatives are able to interact specifically with some of these serine proteases. To understand the enzyme-sorbent interactions we have investigated the ability of two commercially available benzamidine affinity matrices to purify thrombin-like serine proteases (TLSP) with similar biological properties from two snake venoms (Bothrops jararacussu and Lachesis muta rhombeata). Curiously, each sorbent retained a single but distinct TLSP from each venom with high yield. Molecular modeling analysis suggested that hydrophobic interactions within a specific region on the surface of these enzymes could be generated to explain this exquisite specificity. In addition, it was demonstrated that a specific tandem alignment of the two benzamidine sorbents enables the purification of three other enzymes from B. jararacussu venom.

Quantitative determination of the ligand content in Benzamidine Sepharose 4 Fast Flow media with ion-pair chromatography

A quantitative hydrochloric acid hydrolysis-HPLC method was developed for the analysis of the ligand content of Benzamidine Sepharose 4 Fast Flow media. The method requires about 100 mg of dried sample and simple reaction vials can be utilised. Release of the ligand (p-aminobenzamidine) from the base matrix (Sepharose 4 Fast Flow) was obtained after hydrolysis for 180min at 70 degrees C in concentrated hydrochloric acid. When Benzamidine Sepharose 4 Fast Flow media were treated this way p-aminobenzoic acid and p-aminobenzamidine were the only products released from the ligand. A chromatographic system based on ion-pair reversed phase separation was used to quantify these ligand products. The mobile phase was made acidic enough to make p-aminobenzoic acid and p-aminobenzamidine positively charged in order to make ion-pair formation with hexanesulfonic acid possible. The relative standard deviation of th e method was below 2% and no systematic errors could be detected when the results were compared to an independent method based on elemental analysis (nitrogen). The new HPLC method was used to analyse ligand densities in the range of 2-20 micromol/ml medium.

Characterization of p-aminobenzamidine-based sorbent and its use for high-performance affinity chromatography of trypsin-like proteases

An affinity sorbent, hydrophilic polymer-based carrier of different pore size (Toyopearl) with immobilized p-aminobenzamidine (ABA), has been prepared. Its basic properties and some applications for protein purification were studied. ABA, which is a synthetic inhibitor for trypsin-like proteases, was covalently immobilized to Toyopearl by reductive amination. The ligand density and binding capacity for porcine trypsin varied depending on the pore size of Toyopearl. The maximum binding capacity of the immobilized p-aminobenzamidine Toyopearl (ABA-Toyopearl) for trypsin was more than 40 mg/ml gel. ABA-Toyopearl thus obtained was very stable below pH 8 and was successfully used for high-performance affinity chromatography of trypsin-like proteases such as trypsin, thrombin, tissue-type plasminogen activator or urokinase in a single step at 25 degrees C.

Monoclonal antibody against human enterokinase and immunohistochemical localization of the enzyme

A monoclonal antibody, hek-1, was raised against enterokinase or enteropeptidase that had previously been partially purified from human duodenal fluid. Hek-1 showed staining of two glycoprotein bands of relative molecular weights of 260,000 and 240,000 on immunoblot analysis of partially purified enterokinase and of ammonium sulfate fraction of duodenal fluid. An enzyme immunoassay for human enterokinase was developed, making use of hek-1. Sensitivity to enterokinase was 20 times higher than that of the conventional assay where BAPA was used as a substrate. The immunohistochemical study with hek-1 showed staining of the brush border membrane and some goblet cells of the duodenum and upper jejunum but no staining of the colon epithelium.

Receptor-mediated endocytosis of enterokinase by rat liver. Preliminary characterisation of low-density endosomes

The endocytosis of enterokinase by rat hepatocytes has been studied both in a perfused liver system and in the intact, anaesthetised animal. 10 min after administration of the enzyme, only 70% of the activity was cleared by the perfused liver, whereas clearance was total in the intact animal. In both cases, about 85% of the internalised enzyme co-purified with the smooth microsomes and virtually all (more than 90%) of the catalytic activity was latent and could only be detected in the presence of detergent. After 10 min, 22.5% of the activity remained with the sinusoidal plasma membrane in the case of the perfused liver, while for the intact animal this figure was only 10%, confirming the more efficient clearance of enterokinase in the intact animal. Further subcellular fractionation showed that in the anaesthetised animal 8% of the internalised enzyme was associated with a low-density Golgi-like endosomal compartment (prepared from the mitochondrial pellet), whereas the corresponding value for the perfused liver was only 2.5%. Enterokinase specific activity was also up to 50-times greater in the low-density endosomes prepared from the intact animal. A second low-density Golgi-like compartment (purified from the smooth microsomes) also contained latent enterokinase, which together with the endosomes derived from the mitochondria accounted for 20% of the total enterokinase internalised by the liver 10 min after its administration to the intact animal. The passage of enterokinase through these two low-density compartments was shown not to be synchronous with its passage through the peripheral (sinusoidal membrane) and internal endosomes (smooth microsomes). There were qualitative differences in marker enzymes and polypeptide composition between the mitochondria and microsome-derived low-density endosomes. The sub-fractionation of low-density fractions on shallow sucrose gradients revealed a complex enzyme and polypeptide heterogeneity both between and within fractions. There was an apparent density-dependent separation of enterokinase from galactosyltransferase and the asialoglycoprotein receptor which was coincident with marked changes in the polypeptide composition of the endosomal membranes, particularly in the 30-45 kDa range.

Specificity studies on enteropeptidase substrates related to the N-terminus of trypsinogen

The specificity of the synthetic substrate Gly-[L-Asp]4-L-Lys 2-naphthylamide originally developed for the assay of enteropeptidase (EC 3.4.21.9), was investigated with partially purified aminopeptidase. Our results indicate that, not only enteropeptidase, but also the concerted action of the aminopeptidases of the rat small intestine, can rapidly release 2-naphthylamine from the substrate. A previously undescribed, highly active, dipeptidylaminopeptidase, which hydrolyses a Gly-Asp dipeptide from the N-terminus of the substrate, was detected in rat small intestine. The resulting [L-Asp]3-L-Lys 2-naphthylamide fragment is then degraded by a combination of aminopeptidase A and N to yield free 2-naphthylamine. Thus the present substrate cannot be regarded as being specific for enteropeptidase, and its use leads to an over-estimation of enteropeptidase activity in homogenates and extracts of intestinal tissue. In order to prevent this non-specific hydrolysis by aminopeptidases, stereoisomeric substrates with the sequence L-Ala-D-Asp-[L-Asp]3-L-Lys methyl ester, D-Ala-[L-Asp]4-L-Lys methyl ester and L-Ala-[Asp]4-L-Lys methyl ester were synthesized and tested as alternative substrates by their ability to inhibit the enteropeptidase-catalysed activation of trypsinogen.

Intraduct enterokinase is lethal in rats with experimental bile-salt pancreatitis

Controlled intraduct infusion and peri-acinar dispersal of 100 microliter buffer containing sodium glycodeoxycholate (GDOC) at concentrations of 8.5, 17 and 34 mmol/l in rats caused a progressively severe acute pancreatitis from which none of the animals died over the experimental period. Infusion of affinity-purified active human enterokinase in buffer did not cause pancreatitis, presumably because of the inability of the macromolecule to gain access to its specific intracellular substrate trypsinogens. The addition of enterokinase 200 ng to GDOC 34 mmol/l in the infusate resulted in a severe systemic disturbance and a form of acute necrotizing pancreatitis which was uniformly and rapidly lethal. This effect was not seen when equimolar trypsin was substituted for enterokinase. These findings show that enterokinase specifically increases the lethality of experimental bile salt pancreatitis and suggest that this bile-borne enzyme may in some cases pose a significant clinical threat.

The generation of lysolecithin by enterokinase in trypsinogen prophospholipase A2 lecithin mixtures, and its relevance to the pathogenesis of acute necrotising pancreatitis

The cascade enterokinase-trypsinogen-prophospholipase A2 lecithin, generating trypsin, phospholipase A2 and lysolecithin, respectively, was studied in vitro using a novel phospholipase A2 assay. The rate of enterokinase catalysed activation of trypsinogen was maximal at 4 mmol/1 glycodeoxycholic acid; higher concentrations of bile salt progressively inhibited enterokinase activity. Net phospholipase A2 activity in reaction mixtures was critically dependent on the trypsin/prophospholipase A2 molar ratio. Lecithin hydrolysis by phospholipase A2 was dependent on the bile salt/lecithin molar ratio and was optimal at 1.25 to 1. The addition of enterokinase to lecithin and bile salt mixtures, containing trypsinogen and prophospholipase A2 at presumed pathophysiological concentrations, resulted in the generation of concentrations of lysolecithin lytic for pancreatic acinar cells within 5 min. These findings would support the concept that the entry of bile containing active enterokinase into the pancreatic duct system in vivo may in some cases be involved in the initiation of necrotising acute pancreatitis in man.

A rational approach to the specific chemotherapy of pancreatitis

Oedematous pancreatitis is pancreatic acinar cell damage with leakage into the peritoneal cavity and circulation of the inactive zymogens of digestive enzymes and active amylase and lipase. Pancreatic oedema and intra-abdominal fat necrosis occur. Necrotising pancreatitis is pancreatic acinar cell damage accompanied by the specific conversion of trypsinogens to trypsins, at a rate, and on a scale, sufficient to overwhelm local defences. Rapid release of the whole spectrum of activated pancreatic enzymes leads to necrosis of parts of the pancreas and blood vessels, and the disseminated enzyme-mediated damage which characterises the molecular pathology of the established severe disease. Chronic pancreatitis, although less well understood, is also associated with trypsinogen activation within the gland. Two mechanisms have emerged as initiators of trypsinogen activation, lysosomal cathepsins and bile-borne enterokinase. Chemotherapeutic strategies against disease initiation include preparation of synthetic enterokinase and Cathepsin B inhibitors. Chemotherapeutic strategies against second-stage mediation of multi-organ damage in the disease, include oligopeptide or organic functionalities with novel catalytic site-directed moieties (such as fluoromethyl ketones) suitable for in vivo use and the specific inhibition of the relevant range of enzymes in complex with alpha 2-macroglobulin. Interference with pancreatic enzyme biosynthesis using proteolysis-resistant constructs mimicking receptor-binding domains of inhibitor peptide hormones as well as inhibitors of pancreatic signal peptidase are promising additional chemotherapeutic approaches worthy of active investigation.

Displacement of endogenous enterokinase into portal venous blood and bile following luminal perfusion of proximal small intestine in guinea pigs

The displacement of endogenous enterokinase into portal venous blood or bile was studied in conscious guinea pigs both with the small intestine undisturbed and during gentle, intermittent luminal perfusion of a 25-cm segment of duodenum and proximal jejunum. Perfusates tested included water, 150 mM saline, 5% (v/v) ethanol, 0.2% (w/v) lysolecithin, and mixtures of ethanol and lysolecithin. Enterokinase activity was absent from portal venous blood of control guinea pigs with the intestine undisturbed but perfusion with luminal saline or water was consistently associated with substantial levels of active enterokinase in portal venous blood. Similar concentrations of enterokinase in portal blood were also detected in response to luminal ethanol and lysolecithin. The capacity of the normal liver rapidly to clear the enzyme from portal blood was demonstrated. Of the estimated total endogenous enterokinase displaced, 0.2-0.4% was recovered in catalytically active form from the pooled bile of luminally perfused but not control animals. The readiness with which enterokinase was displaced into the circulation in the absence of mucosal damage raises the unexpected possibility that the event may be physiological. Induced penetration of the mucosa and absorption of luminal components is clearly different from the release into portal venous blood of endogenous mucosal macromolecules.

Two-dimensional gel analysis of zymogen-activating factors in the small intestine of the mouse

Zymogen-activating factors in the mouse were investigated by two-dimensional electrophoresis. Mouse pancreatic zymogens--trypsinogen-I group (Try G-I group), trypsinogen-II (Try G-II), and chymotrypsinogen (Chy G)--were purified using DEAE-cellulose column chromatography. Analysis by two-dimensional electrophoresis, using the purified zymogens as substrates, revealed enterokinase isozymes and chymotrypsinogen-activating factors in both the intestinal extract and luminal fluid. Mouse enterokinase was separated into at least two bands in the first-dimensional gel, each able to activate both trypsinogens Try G-I group and Try G-II. Chymotrypsinogen-activating factors were separated into several bands in the first-dimensional gel. Some activating factors showed mobilities similar to those of mouse enterokinase isozymes. Moreover, other activating factors that can activate chymotrypsinogen were present only in the more anodal area of the first-dimensional gel. These findings indicate that at least two enterokinases and several chymotrypsinogen-activating factors play an important role in the process of activating digestive enzymes.

Biliary excretion of enterokinase in rats: studies in alcoholic rats with fatty liver

Ethanol-associated fatty liver was induced in rats fed a nutritionally deficient liquid diet containing 36% of total calories as ethanol. Control rats received the same diet with sucrose substituted isocalorically for ethanol. After 40 days, hepatic lipid content of the ethanol-maintained animals was four-fold greater than controls and ultrastructural changes in hepatocytes were well established. Clearance of intravenously administered human enterokinase from the circulation as well as bile flow were, however, the same in both groups. The proportion of enterokinase appearing in catalytically active form in bile after intravenous injection was substantially greater in the ethanol-maintained animals than the isocaloric controls; the difference was highly significant (p less than 0.001) and reached two- to four-fold after 70 days on the diet. These findings would suggest that the ability of hepatocytes to degrade enterokinase cleared from the blood may be bypassed or impaired by prolonged ethanol consumption and a deficient diet. Catalytically active enterokinase in bile may participate in the development of some types of acute necrotising pancreatitis.

Further studies on the subunit structure and oligosaccharide moiety of human enterokinase

Highly purified human enterokinase was found by SDS-polyacrylamide gel electrophoresis to contain three heavily glycosylated subunits of apparent molecular masses 54 000, 102 000 and 140 000. The smallest subunit contained the active site serine residue and the oligosaccharide chains appear to be N-glycosidically linked as inferred from their stability to mild alkaline hydrolysis. Lectin affinity chromatography was used to separate sub-populations of the enzyme, the major one of which appeared to contain terminal alpha -linked N-acetyl galactosamine. Despite the presence of this sugar, no anti-A response was elicited in rabbits immunized with this sub-population. However, this sub-population did bind rabbit antibody directed against human blood group A substance, suggesting the presence of an "A-like" determinant. Studies with immobilized rabbit anti-human blood group A IgG suggest that there is no correlation between the blood group of an individual and the antigenic determinants on the enterokinase produced by the enterocytes of that individual. The study of the molecular properties of this important enzyme may give insights into pathological conditions with which it is linked.

The biliary excretion of enterokinase in rats. Studies in normal, chronic ethanol-maintained and cirrhotic rats

The excretion of catalytically active human or pig enterokinase in hepatic bile after intravenous administration to normal rats or rats that had been maintained on 20% (v/v) ethanol for 1 year showed similar kinetics to that described for other serum-derived bile proteins. The half-life in serum was 2.5 min or less, and most of the enzyme was excreted within 45 min of administration. This was maintained when up to six successive doses were given at 90 min intervals. The mean amount excreted per dose was independent of the dose number and varied from 0.8% to 2.1% in the normal animals and 1.2% to 2.0% in the chronic ethanol-maintained animals. When three doses of enzyme were given at 30 min intervals, the total amount of active enterokinase recovered in bile was dose-dependent and was consistently higher in the rats drinking 20% (v/v) ethanol. The serum half-life of enterokinase in rats made cirrhotic by inhalation of carbon tetrachloride vapour was extended to 6 min or more. The amount of active enzyme recovered in bile was at least 50% less than in weight-matched normal rats, and excretion was not complete 2h after intravenous administration. The possible significance of these findings in liver and pancreatic disease is discussed.

Specific one-stage method for assay of enterokinase activity by release of radiolabelled activation peptides from alpha-N-[3H]acetyl-trypsinogen and the effect of calcium ions on the enzyme activity

We report a novel assay method for enterokinase capable of detecting approx. 1 fmol of enzyme. The method depends on quantification of the release of specifically radiolabelled activation peptides from bovine trypsinogen and is unaffected by trypsin inhibitors. The assay is applicable to biological fluids such as serum. The substrate was produced by selective epsilon-amidination of bovine trypsinogen followed by acetylation with [3H]acetic anhydride and deprotection. The assay has been used to study the effects of pH, Ca2+, ionic strength abd glycodeoxycholate on enterokinase activity.

Hydrolysis of artificial substrates by enterokinase and trypsin and the development of a sensitive specific assay for enterokinase in serum

The activities of highly purified human enterokinase (enteropeptidase, EC 3.4.21.9) and bovine trypsin were tested against three synthetic substrates alpha-N-Benzoyl-L-arginine ethyl ester HCl, alpha-N-Benzoyl-DL-arginine-p-nitroanilide HCl and alpha-N-Benzoyl-DL-arginine-2-naphthylamide HCl. There was no detectable hydrolysis of these substrates by enterokinase whereas the kinetic parameters obtained for trypsin were in close agreement with those previously described by other workers. The values for Km and kcat were dependent on the Ca2+ concentration. Hydrolysis of glycine-tetra-L-aspartyl-L-lysyl-2-naphthylamide (Gly(Asp)4-Lys-Nap) by these protease was also studied. Enterokinase-catalysed hydrolysis obeyed simple steady-state kinetics and values for Km of 0.525 mM and 0.28 mM and for kcat of 21.5 s-1 and 28.3 s-1 were obtained in 0.1 mM and 10 mM Ca2+, respectively. Trypsin-catalysed hydrolysis was complex and the response to Ca2+ was sigmoidal partly due to the lability of trypsin at low Ca2+ concentrations. A sensitive specific assay for enterokinase was developed and applied to the measurement of the enzyme in serum; interference by nonspecific arylamidases was eliminated by the addition of Zn2+.