The Effect of Temperature and pH on the Stability of Human Pepsin in Stored Gastric Juice: A Method to Prevent Activity Loss

The mechanisms controlling pepsin secretion are controversial. A contributory factor may be storage-dependent effects. We have studied the effects of temperature, pH, and storage time on human gastric pepsin. Gastric juice samples taken from three healthy volunteers under both basal and post-pentagastrin-stimulated (6 micrograms/kg subcutaneously) conditions were separated into four aliquots. Each aliquot was titrated to pH 1, 4, or 6 or left at ambient pH. Aliquots were then stored at 4 degrees C or frozen at -70 degrees C and stored. On days 1, 3, 7, and 28 aliquots were removed and assayed by the kinetic albumin-bromphenol blue method. In a second experiment we determined the effects of different concentrations of glycerol on the preservation of peptic activity. From these experiments we conclude that pepsin is unstable when stored frozen at low pH but not when stored above pH 2. This pH-dependent stability may explain the variable conclusions other workers report on optimal methods of storing gastric juice. In addition, we have confirmed the suitability of glycerol as a preservative of peptic activity and recommend that gastric juice be stored frozen with 11.5% glycerol.