Comparison of the development of proteolytic activity in the abomasum of the preruminant calf with that in the stomach of the young rabbit and guinea-pig

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Abstract
1. Proteolytic activity was measured in the abomasal contents of five calves during the first 7 weeks of life and in the stomach contents of rabbits and guinea-pigs during the first 4 weeks of life.2. The pattern of protease secretion in the abomasum varied considerably among individual calves; in addition to rennin, some pepsin activity was found in most animals from the first sampling at 9 d of age.3. Only pepsin was secreted in the guinea-pig stomach from birth, at a consistently high level at all ages.4. The main peak of proteolytic activity in the rabbit stomach during the 1st week post partum had an optimum at pH 3·5–4·0, corresponding to that for calf rennin. During the 3rd week of life the main pepsin peak, with an optimum at pH 1·6–2·0, developed.5. Agarose gel electrophoresis of an extract of neonatal rabbit stomach mucosa showed the activity peak at pH 3·5–4·0 to be due to two slow-moving components of mobilities similar to that of crystalline rennin. At least one of these cross-reacted with antiserum to crystalline rennin.6. At 10 d and 3 weeks of age, activity at pH 1·6–2·0 was due to two faster-moving proteases, one being the main pepsin of the adult rabbit, which moved at the same speed as crystalline porcine pepsin, with the antiserum of which it cross-reacted.