Pepsin activation volumes

Hj-receptor antagonists almost completely block secretion of hydrochloric acid in the stomach in response to most stimuli. These drugs play a major role in treating stomach ulcers associated with hypersecretion, because they have the ability to reduce both the volume of stomach secretion and overall acidity as well as pepsin activity. 

Figure 7. Emulsifying activity (expressed as volume percentage of the emulsified layer) of pepsin hydrolysates of soy protein as a function of pH and hydrolysis time. No hydrolysis (A) 2 h ( ) 8 h (X) 17 h ( ) 24h(O) (39).

The constancy of the velocity, at the beginning at least, is then established. But how do the dissolved lengths vary when the quantity of pepsin varies As Dudaux, from whom we borrowed the following argument, remarks, we cannot here expect obedience to the law of proportiotnality as in the case of the other procedures where the enz3one and the substance which undergoes the action are uniformly distributed in the same volume of liquid. In the eiq)eriment in question, the entire cylinder of albumin is not in contact with the active liquor, and is attacked only at its base. It is then the quantity of enzyme, not by unit of volume but by unit of surface, which must be considered. 

Another urogastrone material, prepared from human pregnancy urine, has been studied for a number of years by a group at the University of Milan. The most active fraction appears to be a glycoprotein with little or no gonadotropic activity it reduces gastric secretory volume and acid concentration, but has no effect on pepsin concentration in rats. ... 

In our glycine 76 study (Okoniewska et al., 2000), this position was substituted with alanine, valine, and serine. These amino acids differ in their van der Waals volumes, accessible surface areas, polarities, and allowable energy levels on Ramachandran plots for individual amino acids. Rate constants for the activation process were calculated for the mutants and the wild-type enzymes at pH 1.1, 2.0, and 3.0. Samples were taken at different activation times, quenched, and the amount of pepsin formed was determined with synthetic substrate I. Activation rate constants presented in Table 15.5 corresponded to first-order reaction constants. All the mutants activated at rates slower than those for the wild-type, regardless of amino acid size and polarity. At all pH conditions, the activation reactions were slowest for valine and serine mutants, which had comparable reaction rates. The alanine mutant activated more slowly than did the wild-type but was faster than the other two mutants. 

It has long been known (24) that one of the peptides released on activation of pepsinogen could act as a pepsin inhibitor at pH values above 4. Peptide 1-16 from porcine pepsinogen (25) and the corresponding peptide 1-17 from bovine pepsinogen (5) can indeed inhibit the milk-clotting activity of pepsin above pH 5 (see Kumar et, Chapter 13 this volume). ... 

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