Pepsinogen D. A fourth proteolytic zymogen from pig gastric mucosa

The N-terminal sequence of rat pepsinogen

The amino-acid sequence of 96 residues in the N-terminal region of rat pepsinogen I was determined and the first 46 residues were found to constitute the activation peptide segment. There was high degree of homology between the activation segments of rat pepsinogen and some pepsinogens A (pig, cow, Japanese monkey and human). However, the number of residues substituted between rat and the other pepsinogens were considerably larger than those among pepsinogens A. In the N-terminal 24 residues of active pepsin, homology (88%) between rat pepsin and human gastricsin was higher than that (50%) between rat pepsin and pepsin A from human or pig. This strongly suggests that rat pepsin should be classified as pepsin C.

Study of the heterogeneity of bovine pepsin A by pseudo isoelectric focusing

Pseudo isoelectric focusing (PIEF), i.e. focusing stopped before the equilibrium is reached, has been successfully applied to analyse bovine pepsins A obtained from abomasum mucosa extracts and from 3 individual abomasal juices. Whole bovine pepsin A from mucosa extracts, was resolved in PIEF, using an acidic pH gradient(2-4), into five major and active components. Its fractionation on hydroxyapatite only gave four components which were not homogeneous in PIEF, suggesting that interactions between the different components occur during the chromatographic procedure. After treatment with potato acid phosphatase, whole bovine pepsin A showed only one band in PIEF, displaying enzymic activity and with a mobility identical to that of the less anodic band in untreated pepsin. These results, together with organic phosphate determinations, obviously confirm that the heterogeneity of bovine pepsin A is due to the phosphate content which appears to range between 0 and 3 mol./mol. for the 5 components. Two of them, the phosphate content of which appears to be 1 mol./mol., seem to differ in the location of this phosphate group in the molecule. Whole bovine pepsin A preparations from abomasal juices shared the same pattern in PIEF, identical to that observed with bovine pepsin A from mucosa extracts, thus excluding that dephosphorylation might be involved in the secretory process, as well as disproving the theory that dephosphopepsinogen might be an intermediate in the synthesis of pepsinogen, as it was previously suggested.

Characterization of human pepsin I obtained from purified gastric pepsinogen I

Immunochemical homogeneous human pepsinogen I-group (PgI) was purified by solid immunoadsorbent and by DEAE-chromatography from gastric mucosa. PgI contained five electrophoretic distinct bands at pH 8.2 but only four bands at pH 5.6. After acid activation human pepsin (PI) was separated from the inhibitory peptide by affinity chromatography using poly-L-lysine. Purified PgI contained 9-16% of the inhibitory peptide. The yield of PI was 64 to 85%. A 65% increase of specific activity was observed. PI demonstrated three bands in agar gel electrophoresis at pH 5.6. The pH range of PI was rather wide, showing two maxima at pH 2.0 and pH 3.0 with hemoglobin as substrate. Irreverisble inactivation of PI was observed at pH 7.0 and at a temperature of 60 degrees C. The Km-value of PI was 0.170 mmol as determined with N-acetyl-L-phenyl-alanyl-L-3,5 diiodotyrosine. The specific activity was 9.6 IU/mg (hemoglobin substrate) and 0.032 IU/mg (dipeptide substrate). Porc pepsinogen (PPg) and its activated pepsin (PP) was used for comparison. PP showed indentical elution patterns in affinity chromatography. In AEE PPg and PP demonstrated both two components at pH 5.6 with different electrophoretic mobilities. The pH optimum of PP was observed at pH 2.0. PP was slightly more sensitive in alkali and heat inactivation than human P. A higher Km-value of PP of 0.082 mmol and higher specific activity as compared to human PI was observed.

Comparison of the primary structures of acidic proteinases and of their zymogens

From the scattered information about primary structures of aspartate proteinases the following general features appear: 1) Sequence determinations show that two catalytically active aspartic acid residues are located in highly conservative surroundings. 2) Zymogens have so far only been found for extracellular aspartate proteinases of the vertebrates. The zymogens from the gastric mucosa are converted into active enzymes by a limited proteolysis releasing 42 to 44 residues from the NH2-terminus. A common pattern of basic and apolar residues is observed in this NH2-terminal segment. 3) In the presently known structures gastric proteinases and their zymogens have about 40% of all residues in common. The sequence of penicillopepsin shows 18% of identity with the gastric proteinases.

Fractionation and isolation of the multiple forms of prorennin (prochymosin)

The heterogeneity of prorennin was studied by chromatography on DEAE-cellulose and microgranular DEAE-cellulose columns, as well as by polyacrylamide-gel electrophoresis. Prorennin prepared by alum treatment, salting-out and chromatography was resolved into three components by a compound gradient of sodium phosphate on microgranular DEAE-cellulose. Polyacrylamide-gel electrophoresis confirmed the chromatographic results, but crystalline rennin was shown to consist of four bands. When prorennin was isolated directly by chromatography, four zymogen components were resolved on microgranular DEAE-cellulose with a modified compound gradient of sodium phosphate. Polyacrylamide-gel electrophoresis confirmed the existence of four multiple forms of prorennin as well as homogeneity of the chromatographic fractions.

Bovine pepsinogens and pepsins. A series of zymogens and enzymes that differ in organic phosphate content

Several minor pepsinogens, present in extracts of bovine fundic mucosa obtained from the fourth stomach or abomasum, were separated from the main pepsinogen by chromatography on hydroxyapatite at pH7.3. The major pepsinogen and two of these minor pepsinogens were studied in detail. All three zymogens have N-terminal Ser-Val-, C-terminal -Val-Ala and not more than 1mol of glucose/mol of protein; no significant differences in amino acid composition were found. The pepsinogens differ in their organic phosphate content, which accounts for their chromatographic separation. By activation at 0 degrees C and pH2, a corresponding series of pepsins is formed. These enzymes were separated by hydroxyapatite chromatography at pH5.7. All the pepsins have N-terminal valine, C-terminal alanine and are free from carbohydrate. Again the only difference detected among them is in their organic phosphate content. The pepsins of high phosphate content are converted by an acid phosphatase in vitro into pepsins of low phosphate content.

Studies on the heterogeneity of human gastric zymogens

THE PEPTIC ZYMOGENS OF HUMAN GASTRIC MUCOSA HAVE BEEN STUDIED IN THE PAST BY THREE DIFFERENT TECHNIQUES: phosphate-gradient chromatography on a column of DEAE-cellulose, chloride-gradient chromatography on DEAE-cellulose and agar-gel electrophoresis. These techniques have given different results, each suggesting the presence of a different number of pepsin zymogens in human gastric mucosa. In the present experiments gastric mucosal homogenates were subjected to analysis by all three techniques. The two major zymogen peaks obtained from phosphate-gradient chromatography were found to be composed of the three fractions found on chloride-gradient chromatography; these fractions in turn were shown to be heterogeneous on agar-gel electrophoresis. The latter technique demonstrated the presence of seven separable enzymically active components in human gastric mucosal homogenates. The relationships of the components separated by the three techniques are discussed.

Pepsin D. A minor component of commercial pepsin preparations

Methods are described for the isolation and purification of pepsin D, an enzyme which accounts for about 10% of the enzymic activity in commercial preparations of pepsin. Pepsin D is similar to pepsin in having a molecular weight of about 35000, the same C-terminal amino acid sequence, and an N-terminal isoleucine residue. It differs in having no phosphate residue. Pepsin D is similar to pepsin in its ability to digest haemoglobin, acetyl-l-phenylalanyl-l-di-iodotyrosine and gelatin but it is twice as active as pepsin in the clotting of milk. It has the same specificity as pepsin in its action on the B-chain of oxidized insulin. It is probable that the pepsin D in commercial preparations of pepsin arises from the activation of gastric pepsinogen D.