Purification and Characterization of Canine Pepsinogen

Purification and partial characterization of canine pepsinogen A and B

OBJECTIVE

To purify and partially characterize various isoforms of canine pepsinogen (PG) from gastric mucosa.

SAMPLE POPULATION

Stomachs obtained from 6 euthanatized dogs.

PROCEDURE

Mucosa was scraped from canine stomachs, and a crude mucosal extract was prepared and further purified by use of weak anion-exchange chromatography, hydroxyapatite chromatography, size-exclusion chromatography, and strong anion-exchange chromatography. Pepsinogens were characterized by estimation of molecular weights, estimation of their isoelectric points (IEPs), and N-terminal amino acid sequencing.

RESULTS

Two different groups of canine PG were identified after the final strong anion-exchange chromatography: PG A and PG B. Pepsinogens differed in their molecular weights and IER Pepsinogen B appeared to be a dimer with a molecular weight of approximately 34,100 and an IEP of 4.9. Pepsinogen A separated into several isoforms. Molecular weights for the various isoforms of PG A ranged from 34,200 to 42,100, and their IEPs ranged from 4.0 to < 3.0. The N-terminal amino acid sequence for the first 25 amino acid residues for PG A and B had good homology with the amino acid sequences for these proteins in other species.

CONCLUSIONS AND CLINICAL RELEVANCE

Canine PG B and several isoforms of canine PG A have been purified. Availability of these PGs will facilitate development of immunoassays to measure PG in canine serum as a potential diagnostic marker for gastric disorders in dogs.

Purification and characterization of goat pepsinogens and pepsins

Three type-A and two type-C pepsinogens, namely, pepsinogens A-1, A-2, A-3, C-1, and C-2, were purified from adult goat abomasum. Their relative levels in abomasal mucosa were 27, 19, 14, 25, and 15%, respectively. Amino acid compositions were quite similar between isozymogens of respective types, but different between the two types especially in the Glx/Asx and Leu/Ile ratios. NH2-terminal amino acid sequences of pepsinogens A-3 and C-2 were SFFKIPLVKKKSLRQNLIEN- and LVKIPLKKFKSIRETM-, respectively. Pepsins A and C showed maximal hemoglobin-digestive activity at around pH 2 and 3, respectively, and specific activities of pepsins C were higher than those of pepsins A. Two subtypes of pepsin A were obvious, namely pepsin A-2/3 which maintains its activity in the weakly acidic pH region over pH 3 and pepsin A-1, which does not. Hydrolysis of oxidized insulin B chain by goat pepsins A occurred primarily at Ala14-Leu15 and Leu15-Tyr16 bonds.

[Effect of the degree of phosphorylation of bovine pepsin A on its enzymatic activity]

Proteolytic and clotting activities of bovine pepsin A with respect to its degree of phosphorylation were studied on various substrates. The occurrence of phosphate group(s) on bovine pepsin A more or less strongly affects its enzymic properties according to the substrate and its environment. This is particularly obvious as far as kappa-casein is concerned. The specific flocculating activity of unphosphorylated (fA0) as well as dephosphorylated (treated with potato acid phosphatase) bovine pepsin A, determined on a 0.2% kappa-casein solution, is significantly higher than that observed with phosphorylated pepsins, especially after kappa-casein was treated with alpha-D.N-acetyl galactosaminyl oligosaccharidase, while specific milk clotting activity remains unchanged regardless to the level of phosphorylation of bovine pepsin A is. Using haemoglobin as substrate, unphosphorylated pepsin A exhibits the highest specific proteolytic activity and the less acidic pH optimum. Conversely, the amount of phosphate groups does not seem to have any effect on the peptidase activity assayed towards the synthetic chromophoric hexapeptide Leu-Ser-Phe(NO2)-Nle-Ala-Leu-OMe. By treating whole bovine pepsin A with potato acid phosphatase during 24 h at 37 degrees C and pH 5.6, using a 1/100 E/S ratio, almost complete dephosphorylation can be reached. The stability of different bovine pepsin A preparations, more or less phosphorylated, treated or not with phosphatase was also investigated. At pH 2.2, phosphorylated bovine pepsin A is twice more stable at 37 degrees C than the dephosphorylated enzymes while dephosphorylated pepsin does not exhibit any degradation at pH 5.6, judging by isoelectric focusing patterns, or loss of activity. Such a result suggests that post-translational phosphorylation might play an essential physiological function by improving the stability and integrity of pepsin in the bovine abomasum, the pH of which is very acidic (between 1.0 and 2.0).

Isolation and characterization of camel pepsins

Camel (Camelus dromedarius) pepsins were precipitated from the extract of the fundic gastric mucosa by ammonium sulfate between 35 and 80% saturation. DEAE--cellulose chromatography of this fraction produced two isoenzymes, I and II, which were further purified to homogeneity on sephadex G-100. Their Km with N-acetyl-L-phenylalanyl-diiodotyrosine were 0.10 and 0.90 mM, and their molecular weights which were determined on sodium dodecylsulfate gel electrophoresis exhibited 35,500 and 34,700, respectively. The two pepsins were essentially free of carbohydrates, but contained 0.3 and 1.0 mol of organic phosphate per 1 mol of protein, respectively. The apparent mobilities of the phospho- and dephosphoforms of each pepsin were indifferent in polyacrylamide gel electrophoresis at pH 8.9. The N-terminal residues of pepsins I and II were found to be alanine and leucine, respectively. Pepsin I was inactivated at a faster rate than that of pepsin II at pH 8 and 0 degrees C, and at pH 7.5 and 37 degrees C; but both were denatured under these conditions. The properties of these enzymes are compared with those of other mammalian and avian pepsins.

A pepsinogen from dog stomach

1. A pepsinogen has been purified from dog stomach in 20% yield. 2. At pH values below 4 it spontaneously converts to a pepsin, the first order rate constant at pH 2, 22 degrees C, being 11 min-1. 3. The pepsinogen is stable to denaturation at pH values up to 9, in contrast to the pepsin which is irreversibly denatured above pH 7. 4. Its proteolytic activity against denatured hemoglobin is equal to that of pig pepsin, but in the milk-clotting assay at pH 5.5 its has only 14% the activity.

Partial characterization of pepsins and gastricsins and their zymogens from human and toad gastric mucosae

1. Three zymogens have been isolated from human gastric mucosae and two from the stomachs of the toad Caudiverbera caudiverbera. 2. Human zymogens I and III were immunologically related and cross-reacted with antisera prepared against porcine pepsinogen. The third, (II), showed no cross-reactivity. 3. Human zymogens I and III and toad zymogen ZII gave rise to two human pepsins and to a pepsin-like enzyme, respectively. 4. Human zymogen II (gastricsinogen) and toad zymogen ZI gave rise to human gastricsin and to a gastricsin-like enzyme respectively. 5. The toad enzymes showed much greater stability at neutral and alkaline pH values than the human enzymes.

The first cleavage site in pepsinogen activation

By incubation of porcine, bovine, canine, or chicken pepsinogens and calf prochymosin with pepstatin at pH 2.5, the first active protein generated on activation is trapped in an inactive complex. The first activation peptide liberated from porcine pepsinogen has been identified as residues 1-16 whereas that from prochymosin is derived from residues 1-27. This suggests that pepsin and chymosin are not formed by one-step conversions from their zymogens, but by (different) sequential, activation mechanisms.