In vitro digestion of gliadin by gastrointestinal enzymes and by pyrrolidonecarboxylate peptidase

The enzymatic hydrolysis of whole gliadin has been studied in vitro using sequential treatments by pepsin, trypsin, and pancreatin. Amino-terminal pyroglutamic acid-peptides were formed at each stage of the digestion process and the concentration of these peptides increased as the hydrolysis proceeded. Digests were further fractionated on columns of AG 50W-X8 or SE-Sephadex. Enzymic digests and selected column fractions were analyzed with pyrrolidonecarboxylate peptidase. Each digest or fraction was degraded further by this peptidase. Enzyme activity was greatest towards peptic-tryptic-pancreatic digests, peptic-tryptic digests, peptic digests, and undigested gliadin, in that order. The stability of lysosomal membranes to synthetic L-pyroglutamic acid, L-pyroglutamyl-L-alanine, L-pyroglutamyl-L-proline, and to selected fractions of the enzymic digests was tested. Each treatment ruptured lysosomal membranes. Findings are discussed in relation to the normal catabolism of gliadin and the alterations that may occur in certain pathological states.