Glycylglycine dipeptidase

There are many dipeptidases [EC 3.4.13.x]. Cytosol nonspecific dipeptidase [EC 3.4.13.18] (also referred to as peptidase A, glycylglycine dipeptidase, glycylleucine dipeptidase, and A -)3-alanylarginine dipeptidase) catalyzes the hydrolysis of dipeptides. Membrane dipeptidase [EC 3.1.13.19] (also known as microsomal dipeptidase, renal dipeptidase, and dehydropeptidase I) is a zinc-dependent enzyme (a member of the peptidase family M19) that also catalyzes the hydrolysis of dipeptides. 

Found to be subject to metal ion catalysis, but the discovery by Kroll in 1952 that the hydrolysis af a-amino acid esters was catalyzed by metal ions stimulated considerable interest in the area. Many of these reactions can be considered as simple model systems for such metalloenzymes as arboxypeptidase A, leucine aminopeptidase and glycylglycine dipeptidase.25... 

One of the earliest suggestions that total enzymatic hydrolysis was possible came from the studies of Frankel (1916), who showed that over 90 % of the bonds in several proteins could be broken when proteolysis with pepsin, trypsin, and chymotrypsin was followed by prolonged hydrolysis with the erepsin preparation of Cohnheim (1901). The recognition in later years of several peptidases in intestinal exti acts which will specifically act upon bonds that are not susceptible to the endopoptidases (Bcrg-mann, 1942) probably accounts for these obseiwations. The specific peptidases such as prolidase, iminodipeptidase (prolinase), glycylglycine dipeptidase, tripeptidase, and leucine aminopeptidase, whi( h are present in mucosa, attack many of the bonds that resist the action of endopoptidases. 

The foregoing examples of transfer involve an amide radical. There are several instances of amino acid transfer at a peptide bond. Frantz and Zamecnik (58,142) found that when glycylglycine is hydrolyzed by a dipeptidase in the presence of C -labeled glycine, at equilibrium the theoretical amount of labeled glycine is found in the dipeptide but, when the reaction is stopped short of equilibrium, there is more than the equilibrium amount of labeled glycine in the dipeptide. The same was found with carboxypeptidase. In both instances the degree of replacement was low and much less than the degree of hydrolysis. 

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