[Amino acid composition of unresorbed peptide fractions in the contents of the distal part of rat small intestine. 1. Nitrogen-free diet and diets with casein, sunflower protein isolate and defatted sunflower seeds].

After feeding with protein containing diets the protein quantity increases in the aqueous supernatant (U1), in the trichloracetic acid soluble (U2) and precipitable (S2) fractions of the content of the distal part of the small intestine of rats. Independent of the dietary proteins the amino acid composition of both fractions (S2 and the peptides from U2) is similar in relation to protein-free feeding; a similarity with the amino acid composition of the dietary proteins doesn't exist. In relation to fraction S2 the peptides of fraction U2 show anording to the higher content of amino acids, which are difficult to liberate by protein cleavage, a high proteolytic degradation.