Ovalbumin digestion by human pepsins 1, 3 and 5.

1. Of the three major human pepsins, pepsin 1 has greater proteolytic activity towards ovalbumin than has pepsin 3. Pepsin 5 has low activity towards this substrate. 2. Proteolytic pH-activity curves show only on pH maximum, about pH 1.4 for pepsin 1, pH 1.4--1.5 for pepsin 3 and pH 1.2--1.4 for pepsin 5. The curve for pepsin 3 has a shoulder between pH 2.4 and 3.4. 3. The rate of digestion of ovalbumin by pepsin 1 is approximately three times slower than are those of bovine haemoglobin or human globin. 4. The results suggest that there may be a physiological advantage in having more than one pepsin.