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The Role of Pepsin, Peptic Inhibitory Substances, and Hydrochloric Acid in Normal Subjects and in the Production of Peptic Ulcers

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The Role of Pepsin, Peptic Inhibitory Substances, and Hydrochloric Acid in Normal Subjects and in the Production of Peptic Ulcers THE ROLE OF PEPSIN, PEPTIC INHIBITORY SUBSTANCES, AND HYDROCHLORIC ACID IN NORMAL SUBJECTS AND IN THE PRODUCTION OF PEPTIC ULCERS Harry H. Le Veen, Leonard Hallinger J Clin Invest. 1947;26(4):761-772. https://doi.org/10.1172/JCI101859. Research Article Find the latest version: https://jci.me/101859/pdf THE ROLE OF PEPSIN, PEPTIC INHIBITORY SUBSTANCES, AND HYDROCHLORIC ACID IN NORMAL SUBJECTS AND IN THE PRODUCTION OF PEPTIC ULCERS 1 By HARRY H. LE VEEN AND LEONARD HALLINGER (From the Department of Surgery of the University of Chicago) (Received for publication July 23, 1946) INTRODUCTION chloric acid solution. Such ulcers were not pro- There is still disagreement as to the respective duced by perfusion with hydrochloric acid alone. roles of the pepsin and hydrochloric acid of gastric Driver's (14) investigations with dogs have juice in the production of duodenal ulcer. yielded comparable results. Matzner (15) was In patients with ulcer, free hydrochloric acid has able to produce ulcers in rats by feeding pepsin- been generally found to be present in increased hydrochloric acid mixtures. quantities (1, 2). The work of Dragstedt (3) and In any attempt to resolve the controversy over of Mann and Bollman (4) have tended to empha- the comparative importance of acid and pepsin, it size the importance of hydrochloric acid. is necessary to apply more refined quantitative The occurrence of ulcers following the surgical methods of study and to devise mutually exclusive shunting of alkaline secretions (bile and pancreatic experimental conditions wherein both factors do juice) away from those portions of intestines where not vary in the same direction simultaneously. gastric juice was made to enter, served in part as Accurate determinations of gastric hydrochloric a basis for their deductions. Dragstedt, in addi- acid are easily made, but most methods for deter- tion, pointed out that the rate of digestion of frog's mining pepsin have been either inadequate or cum- leg in an acid pepsin solution was dependent on bersome (16). The reason for inadequacy lies acid concentration and independent of pepsin con- partially in the method and partially in the fail- centration (5). The production of ulcers by feed- ure to take cognizance of the kinetics of the enzyme ing hydrochloric acid to experimental animals also (pepsin) reaction. served as a basis for their conclusions. Histamine is a potent secretagogue of hydrochloric acid (6), THE KINETICS OF THE ENZYME REACTION but not of pepsin (7). Ulcers have been produced Pepsin acts on proteins, splitting them into pro- in practically all species of animals by injection of teoses, peptones, and polypeptides, but not to the histamine in beeswax (8). Cases have even been amino acid state (17). In the case of egg albumen, reported in humans following injections of hista- the molecule is either attacked and broken down mine (9). Frequent success over a long period to a molecular weight of approximately 1,000, or with therapy employing antacids has been another it is not attacked at all (18). Pepsin has a pre- strong argument in support of this premise. dilection for certain peptide linkages, especially Vanzant, Osterberg, Alvarez, and Rivers (10) those involving tyrosine and phenylalanine (19). have shown that the secretion of pepsin is enhanced Unlike linkages are split at various rates (19). in ulcer patients as compared with normal indi- Pepsin does not act like some simple inorganic viduals and that a direct correlation existed be- catalysts whose mere presence in traces is sufficient tween the amount of pepsin in gastric juice and the to bring about change. This enzyme reaction has severity of symptoms. Mullins and Flood (11) been found to obey the Law of Mass Action, so and others (12) have confirmed these observa- that the rate of reaction and therefore the amount tions. Schiffrin (13) demonstrated that ulcers of substance converted are directly proportional could be produced by perfusing isolated loops of both to the amount of active enzyme and to the jejunum or ileum of cats with pepsin and hydro- concentration of active substrate present. How- 1 Done on a grant from the Otho S. A. Sprague Me- ever, the rate of conversion is not uniform for morial Institute. more than a brief period. The reaction rate rap- 761 762 HARRY H. LE VEEN AND LEONARD HALLINGER is liberated from the pepsin-peptone complex and 24, additional digestion occurs. The significance of 2.0. these concepts will be enlarged upon later in this C w paper. to 1.6. The rate of digestion, as heretofore mentioned, a is directly proportional to the rate of concentration z 1.2 of the active substrate (21) which is steadily di- minishing during digestion. This, together with - . the fact that the enzyme is being progressively in- l activated during digestion, does not allow for the expression of a direct linear relationship between it 20 6'050 40 0 the enzymenzym concentration and the amount of pro- tein digested under practical test conditions. Nor- TIblE IN MINUTES throp (20) has found the kinetics of the reaction FIG. 1. THE AMOUNT OF PROTEIN DIGESTED IS PLOTTED to conform to the following equation: AGAINST TIME IN MINUTES. THE RATE OF DIGESTION STEADILY DECREASES, REACHING A PLATEAU IN 30 MINUTES A Log A- x A- x K ET K idly diminishes and approaches zero (Figure 1). A = Substrate concentration Peptones,2 the product of pepsin digestion, com- x = Quantity of substrate converted bine with the active enzyme to form an inactive E = Total enzyme concentration (active and pepsin complex. Therefore the quantity of active inactive) enzyme present is constantly diminishing as di- T = Time. progresses. reaction rate has gestion After the Under the conditions of our test, leveled off, the addition of sizeable increment of experimental the amount of protein digested is directly propor- enzyme fails to produce further digestion, since the tional to the logarithm of the total pepsin concen- small quantity of pepsin initially present has pro- It tration (Figure 2). duced large amounts of peptone inhibitor. Protein is an amphoteric substance and is pres- is the concentration of these inhibitory substances ent in the in a acid to its which is form of kations solution which determines the amount of pepsin isoelectric point (22). Pepsin acts only on pepsin active. kations. (The effect of hydrogen ion concentra- This pepsin-peptone complex has also been tion on pepsin digestion is purely on the substrate found Northrop (20) to obey the Law of Mass by and not on the enzyme [23].) Action, so that the following equation applies: The percentage of protein present in its kationic Pepsin + Peptone ±; Pepsin-Peptone form increases as the pH of the solvent decreases and until 100 per cent is in the kationic form. There- after, further decrement in pH will reduce the num- Conc. pepsin X Conc. peptone = K. ber of protein kations by the common ion effect. Conc. pepsin-peptone An increase in the active kationic substrate, The equation illustrates the reversibility of the brought about by pH changes, augments the rate reaction. Thus, if one decreases the concentration of digestion according to the Law of Mass Action. of the peptone inhibitors by dilution, active enzyme Since the pH at which all protein is in its kationic form varies from protein to protein, the optimum 2 Northrop uses the word "peptones" loosely to in- digestion pH of proteins differs. Peptic digestion clude all those breakdown products of protein which of mucosa mimics egg albumen in that both have combine with pepsin. We have retained his definition. their optimum digestion pH in the region of 1 We have also included gastric inhibitory substances with peptones, since they certainly react like them and for the (24). The digestion of mucosa may therefore be purposes of this paper may be considered identical. compared to egg albumen. PEPSIN AND HCL IN PRODUCTION OF PEPTIC ULCER 763 I-1 T /1*, _ 1000C 1~~~~~~~~-7 w~~~ a.~ ~104 4~~~~~~~~~~~~4 2w, /_ I 1_1_'_I IL- t 7 Co 04 / z 3 4 MG. ALBUMEN DIGESTED FIG. 2. THE NUMBER OF MILLIGRAMS ALBUMEN DIGESTED IS PLOTTED AGAINST GAMMA OF CRYSTALLINE PEPSIN ON SEMILOGARITHMIC PAPER FOR BOTH THE DILUTE AND THE CONCENTRATED TESTS In the concentrated test, 2% x the enzyme concentration produces 20 X the amount of albumen digested. APPLICATION OF ENZYME KINETICS TO THE STUDY (28) indicated that these substances were prob- OF GASTRIC JUICE ably peptones. It may be that the inhibitors of In gastric juice, the estimation of pepsin activity the gastric juice are peptones formed by the action is complicated by the presence of inhibitory sub- of pepsin on proteins derived from food, mucosal stances analogous to peptones (25). These sub- cells, and secreted protein (mucin and plasma stances, formerly called anti-enzymes (26), have protein). been thought to play an active role in protecting Dilution of gastric juice, under any conditions, against autodigestion (26, 27). Langenski6ld by decreasing the concentration of inhibitory sub- 764 HARRY H. LE VEEN AND LEONARD HALLINGER stances (peptones), allows digestion to continue composed has been constructed (Figure 3). (This unimpeded. By using highly diluted juice one can relationship is observed only in low dilutions.) assay the total quantity of pepsin present un- This establishes that one can interpolate to the affected by the naturally occurring inhibitory sub- undiluted state in order to determine the amount stances. Conversely, when one uses low dilutions, of pepsin in gastric juice that remains unaffected one assays only that fraction of pepsin which is by the inhibitory substances present (30). uncombined with the naturally occurring inhibi- We have assayed Total Pepsin Activity at opti- tory substances, which we have called the Active mum pH utilizing high dilutions of gastric juice Fraction.
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