[Characteristics of hydrolytic protein breakdown at an early age]

Proteolysis of milk proteins occurring within the gastrointestinal tract was distinctly manifested in young rats during the period of milk feeding as shown by gel filtration of nitrogenous components from contents of various parts of small intestine of 3, 20 and 30 days old rats as well as by means of ion exchange chromatography of free amino acids and estimation of their concentration and the rate of the amino acids liberation after incubation of the content of these parts of the intestine in vitro. In 3-20 days old rats the cavitary proteolysis was competed in the distal part of small intestine, in adult animals--in the proximal part. The amino acids might be divided into two groups: the rapidly liberated substances (leucine, isoleucine, lysine, arginine, tyrosine, serine) and the slowly liberated compounds (proline, glutamic and aspartic acids). The data obtained suggest the existance of two types of protein digestion--cavitary and intracellular (and/or membrane type) during this period of the ontogenesis; concepts of alimentary specificity of caseins are also discussed.