Hydrolysis of peptides within lumen of small intestine

Abstract

The quantitative significance of intraluminal peptide hydrolases in the terminal stages of peptide digestion was investigated, and the precise origins of these enzymes were determined. Intestinal contents and mucosae were obtained from rats anesthetized with ether. Experiments carried out on pancreaticobiliary secretions and germfree rats showed that pancreatic and bacterial enzymes do not contribute significantly toward the luminal digestion of dipeptides. Chemical assay data, thermostability studies and examination of electrophoretic mobilities of luminal peptide hydrolases indicated that jejunal enzymes originated predominantly from the cytoplasm of intestinal mucosal cells, whereas the brush border of mucosal cells was a major source of the enzymes in the ileum. With glycyl-L-phenylalanine and L-phenylalanyl-glycine as substrates, jejunal luminal activity was less than 2.6% of mucosal activity. Brush-border peptide hydrolase activity in ileal contents was 11.9% and 40.7% of mucosal brush-border activity for the 2 substrates. Luminal enzymes played an insignificant role in the terminal digestion of peptides in the jejunum, but had a much more important role in the ileal digestion of peptides.