Labile glutamine peptides, and their bearing on the origin of the ammonia set free during the enzymic digestion of proteins

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Abstract
The 3 peptides, d-glutaminylglycine, d-glutaminyl-d-glutamic acid and d-glutaminylglycylglycine, were synthesized by the method of Bergmann and Zervas. All are readily hydrolyzed by yeast peptidases and exhibit the labile characters of d-glutamine itself; i.e., they give abnormally high amino-N (Van Slyke) values and are unstable in aqueous soln. at 100[degree]. The stability of d-glutamine and the peptides mentioned was detd. at 37[degree] and various pH values. All the annde-N is hydrolyzed to ammonia in 6-9 days. The bearing that these observations have on the origin of the ammonia liberated during the enzymic digestion of proteins and also on the titrimetric technic generally used to follow the course of the digestion is briefly discussed.