Dipeptide hydrolases

Dipeptide hydrolases are specific for dipepfide and consequently can not be classified as amino- or carboxypeptidases. However, these enzymes are not important for foods. 

Accuretic Acequide Koretic Quinapril Quinaprilum. component of Accuretic Acequide Koretic. Angiotensin-converting enzyme inhibitor. Orally active peptidyl-dipeptide hydrolase inhibitor. Antihypertensive. Parke-Davis. 

Peptidyl dipeptidase, peptidyl-dipeptide hydrolase, a term initially used to denote enzymes cleaving C-terminal dipeptides from longer peptide substrates. In 1972, this entry was referred by the lUB to angiotensin-converting enzyme (ACE). 

Dipeptidases - Dipeptide hydrolases 3.4.13 Small intestine Dipeptides... 

A different type of peptide hydrolase, dipeptide transferase, catalyzed the oligomerization of dipeptide amides. In the case of glycyl-L-tyrosinamide, the corresponding oligomer with DP up to 8 was formed.242... 

Proteases, which catalyze hydrolysis of peptide bonds in proteins or peptides, are essential enzymes in all types of organisms and, therefore, have been studied in detail by many researchers. In contrast, degradation of DKPs (2,5-diketopiperazines, 2,5-dioxopiperazines, cyclic dipeptides), which have peptide bonds in their molecules, is poorly imderstood in spite of their wide distribution in nature and their unique biological activities, e.g., antimicrobial, anticancer, and so on [1,2]. Therefore, there is no reports on DKP-hydrolyzing enzyme except for a cyclo(Gly-Gly) hydrolase from Bacillus sp.[3j. 

Few other peptide hydrolases from thermophiles have been purified. Cho et al. [299] in studying the aminoacylase from the moderate thermophile Bacillus thermoglucosidus found it to have hydrolytic activity against several dipeptides and mention a dipeptidase with high activity against L-valyl-L-alanine, but no characterization was undertaken. Subsequent screening of Bacillus species for... 

This may arise, for example, when a dipeptide containing L-lysine and a catabo-lizable amino acid such as L-alanine is taken up and hydrolyzed by constitutive di- and oligopeptide uptake and hydrolase systems [39, 40]. Synthesis of LysE is controlled by LysG and occurs only if the intracellular L-lysine concentrations exceeds a threshold of about 35 mM [42]. L-Lysine export could be improved fivefold by overexpression of lysE [39,40]. Expression of lysE under control of an L-lysine riboswitch was also applied (see below [43]). 

Classical enzymes employed for peptide coupling of the serine hydrolase family are chymotrypsin, trypsin, and subtilisin. Chymotrypsin and trypsin are secreted in the mammalian gut as inactive precursors, which are activated by autoproteolysis and structural reorganization. The use of chymotrypsin for peptide synthesis has been reported since the 1930s [50]. Most early examples concern peptide s)mthesis using amides or (m)ethyl esters as acyl donors and free amino acids and their amides, short peptides, or short peptide amides as nucleophilic acyl acceptors [3]. These studies revealed that a high pH, high nucleophile concentration, and low product solubility stimulate the formation of synthetic product. Ethyl esters appeared suitable acyl donors in kinetically controlled conversions, and amino acid amides act better as nucleophilic acyl acceptors than the free amino acids [4]. Furthermore, tripeptides often performed better than dipeptides or amino acids as acyl acceptors. 

Prolyl aminopeptidases (PAP) are exopeptidases that hydrolytically cleave off an N-terminal Pro from peptides. The enzymes belong to the a/p hydrolase fold proteins. A PAP from Streptomyces thermoluteus carrying the active site nucleophile mutation S144C was used as a catalyst for the synthesis of proline-containing peptides. Dipeptide synthesis was obtained with an amino acid methyl or benzyl ester as the acyl donor and prolyl-OBz as the nucleophile [21]. Under alkaline conditions, cycli-zation and polymerization of prolyl-OBz was observed. 

The purified enzyme displays its highest activity at 50°C. Furthermore, the enzyme is fairly stable because more than 90% of the activity is retained after a preincubation for 30 min up to 55°C. The L-aminoamidase is active between pH values of 6.5-11.0, with a broad pH optimum at pH values of 8.0-9.5 (Fig. 9). Determination of the substrate specificity of the purified enzyme showed that this amide hydrolase was active toward a rather broad range of bodi a-H- and a-alkyl-substituted amino acid amides (Table 8). Within these two substrate classes, highest activity is observed for file cyclic amino acid amide DL-proline amide and the a-alkyl-substituted amino acid amides DL-isovaline amide and DL-a-allylalanine amide. Furthermore, this enzyme displays modest activity toward a number of simple amides (e.g., acetamide and propionamide). The enzyme appears to be inactive with the a-hydroxy acid amide DL-mandelic acid amide and with the dipeptide L-Phe-L-Leu. These results clearly show that this purified amide hydrolase belongs to the group of aminoamidases. 

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