Rennin and pepsin in stomachs of rats (Rattus norvegicus).

The predominant protease in adult rat stomachs has a pH optimum of 2.0 to 2.3 which corresponds almost exactly to that of porcine pepsin. One-day-old rats have a protease with a pH optimum of 3.8 to 4.2 similar to that of calf rennin. The pH optimum of rat stomach proteases decreases with age, and at 28 days it is similar to that of the adult. The pH of stomach contents of rats decreases with age from pH 5.8 to pH 4.6. These data support the contention by other workers that the onset of pepsin secretion is a prerequisite for weaning and that rennin-like enzymes are not unique to ruminant species.