In Vitro Digestibility of Succinylated Protein by Pepsin and Pancreatic Proteases

Succinylated and untreated casein were hydrolyzed with pepsin and pancreatin. Neither Nɛ‐succinyllysine nor lysine was detected in the hydrolysate of succinylated casein, although the formation of lysine from untreated casein was detected. The composition of other amino acids from the hydrolysate was similar to that found in the untreated casein. The succinylation of casein suppressed tryptic hydrolysis, but had no influence on chymotryptic hydrolysis. Nα‐tosyl‐lysine‐methylester and its Nɛ‐succinylated derivative inhibited the activity of chymotrypsin to the same extent. Neither carboxy‐peptidases A nor B released Nɛ‐succinyl‐lysine from t‐butyloxycarbonyl‐glycyl‐Nɛ‐succinyl‐lysine. These results reveal that the lysyl bonds of succinylated proteins are not hydrolyzed by proteases present in digestive glands.