Aminopeptidases aminopeptidase

Glutamyl aminopeptidase Aminopeptidase A, Zinc, calcium 1,10-Phenantroline [158],... 

Leueyl aminopeptidase Aminopeptidase I, Zinc, a-Aminoboronic acid... 

Significantly, the approach of activity profiling for cysteine proteases has established cathepsin L as a new protease pathway for neuropeptide biosynthesis. Together with current knowledge in the field, these data demonstrate the existence of two distinct protease pathways for converting proneuropeptides into active peptide neurotransmitters and hormones. These dual pathways consist of the newly discovered cysteine protease pathway for proneuropeptide processing, which consists of cathepsin L followed by Arg/Lys aminopeptidase (aminopeptidase B), and the previously known proprotein convertase (PC) family of subtilisin-like proteases (15-17) that process proneuropeptides with carboxypeptidase E (Fig. 3). Elucidation of these two protease pathways resulted from the application of the biochemical criteria required for processing proteases. 

Most exopeptidases are metalloproteases (exceptions e.g. D-amino acid aminopep-tidase, Salmonella methionine aminopeptidase). Aminopeptidases catalyze the hydrolysis of amino acid residues from the N-terminus of peptide substrates with broad substrate specificity. However, carboxypeptidases hydrolyze C-terminal amino acids with varied substrate specificity. Carboxypeptidase A, which prefers large hydrophobic side chain for the C-terminal residue of peptide substrates, has been extensively investigated (Christianson and Lipcomb, 1989) and its catalytic mechanism is illustrated in Figure 12.9. An analogous mechanism has been proposed for the requiring aminopeptidases (Taylor, 1993). 

In vivo, both bestatin and thiorphan display antinociceptive properties in behavioural tests which are additive when the two inhibitors are coadministered [26,32]. Puromycin does not display similar activity. Taken together, these data strongly indicate that enkephalinase and puromycin insensitive aminopeptidase (aminopeptidase M) are involved in the metabolism of endogenous enkephalins. 

In the placenta, the aminopeptidase oxytocinase, ie, cysteine aminopeptidase, is a principal catalyst for oxytocia hydrolysis and prevents premature uterine contractions. 

Several enzymes, none of which are completely specific for the enkephalins, are known to cleave Leu- and Met-enkephalin at various peptide bonds. The main enzymes that degrade enkephalin are 2inc metaHopeptidases. The first enkephalin-degrading enzyme to be identified, an aminopeptidase which cleaves the amino terminal Tyr-Gly bond (179), has been shown to be aminopeptidase-N (APN) (180). It is a cytoplasmic enzyme which is uniformly distributed throughout the brain. The increased analgesic activity of synthetic enkephalins substituted by D-amino acids at position 2, eg,... 

Ubenimex, [(2(3),3(R))-3-amino-2-hydroxy-4-phenylbutanoyl]-L-leucine, was isolated as an inhibitor of aminopeptidases, on which it acts as a strong, reversible transition-state analogue inhibitor (293). Analogues of ubenimex have been made and some other aminopeptidase inhibitors, not all of them peptides, have been isolated from streptomycetes (294—296). 

Dipeptidyl aminopeptidase (from rat brain) [9031-94-1] [EC 3.4.11.10]. Purified about 2000-fold by column chromatography on CM-cellulose, hydroxylapatite and Gly-Pro AH-Sepharose. [Imai et al. J Biochem (Tokyo)93 431 1983.]... 

L-Amino adds could be produced from D,L-aminonitriles with 50% conversion using Pseudomonas putida and Brembacterium sp respectively, the remainder being the corresponding D-amino add amide. However, this does not prove the presence of a stereoselective nitrilase. It is more likely that the nitrile hydratase converts the D,L-nitrile into the D,L-amino add amide, where upon a L-spedfic amidase converts the amide further into 50% L-amino add and 50% D-amino add amide. In this respect the method has no real advantage over the process of using a stereospecific L-aminopeptidase (vide supra). 

An exopeptidase that sequentially releases an amino acid from the N-terminus of a protein or peptide. Examples include cystinyl aminopeptidase (MEROPS M01.011), which removes a terminal cysteine from the biologically important peptides oxytocin and vasopressin, and methionyl aminopeptidase (M24.001), which removes the initiating methionine from cytosolic... 

Systematic screening experiments have identified more than 100 synthetic compounds with potent antiangiogenic activity. The mode of action for most of these molecules is not well understood, but some of the 40 compounds are well advanced in clinical trials (Table 3). The first substance to have entered clinical trials was the Fumagillin-derivative AGM 1470. Fumagillin is an antibiotic which inhibits bFGF- and PDGF-induced endothelial cell proliferation. The mechanism of action of AGM 1470 is poorly understood, but it was shown that it binds and inhibits the metalloprotease methionine aminopeptidase (MetAp-2). 

T-cell activating antigen although the aminopeptidase and immunological functions do not appear to interfere with each other. 

MG M24 M24.002 Methionyl aminopeptidase 2 Target of the potent angiogenesis inhibitors fumagillin and ovalicin... 

There are several different types of exopeptidases aminopeptidases, carboxypeptidases, dipeptidyl-peptidases, tripeptidy 1-peptidases, peptidyl-... 

Gener ally, a family of peptidases contains either exopeptidases or endopeptidases, but there are exceptions. Family Cl contains not only endopeptidases such as cathepsin L, but also the aminopeptidase bleomycin hydrolase. Some members of this family can act as exopeptidases as well as endopeptidases. For example, cathepsin B also acts as a peptidyl-dipeptidase, and... 

Inhibitors which interact only with peptidases of one catalytic type include pepstatin (aspartic peptidases) E64 (cysteine peptidases from clan CA) diisopropyl fluorophosphates (DFP) and phenylmethane sulfonyl-fluoride (PMSF) (serine peptidases). Bestatin is a useful inhibitor of aminopeptidases. 

Amiloride-sensitive Na+ Channel y-Aminobutyric Acid (GABA) Aminoglycosides Aminopeptidase AMP, Cyclic... 

Racemic a-amino amides and a-hydroxy amides have been hydrolyzed enantio-selectively by amidases. Both L-selective and o-selective amidases are known. For example, a purified L-selective amidase from Ochrobactrum anthropi combines a very broad substrate specificity with a high enantioselectivity on a-hydrogen and a,a-disubstituted a-amino acid amides, a-hydroxyacid amides, and a-N-hydroxya-mino acid amides [102]. A racemase (a-amino-e-caprolactam racemase, EC 5.1.1.15) converts the o-aminopeptidase-catalyzed hydrolysis of a-amino acid amides into a DKR (Figure 6.38) [103]. 

Other interesting examples of proteases that exhibit promiscuous behavior are proline dipeptidase from Alteromonas sp. JD6.5, whose original activity is to cleave a dipeptide bond with a prolyl residue at the carboxy terminus [121, 122] and aminopeptidase P (AMPP) from E. coli, which is a prohne-specific peptidase that catalyzes the hydrolysis of N-terminal peptide bonds containing a proline residue [123, 124]. Both enzymes exhibit phosphotriesterase activity. This means that they are capable of catalyzing the reaction that does not exist in nature. It is of particular importance, since they can hydrolyze unnatural substrates - triesters of phosphoric acid and diesters of phosphonic acids - such as organophosphorus pesticides or organophosphoms warfare agents (Scheme 5.25) [125]. 

Many other peptides are synthesized as proproteins that require modifications before attaining biologic activity. Many of the posttranslational modifications involve the removal of amino terminal amino acid residues by specific aminopeptidases. Collagen, an abundant protein in the extracellular spaces of higher eukaryotes, is synthesized as procollagen. Three procol-... 

There are two main classes of proteolytic digestive enzymes (proteases), with different specificities for the amino acids forming the peptide bond to be hydrolyzed. Endopeptidases hydrolyze peptide bonds between specific amino acids throughout the molecule. They are the first enzymes to act, yielding a larger number of smaller fragments, eg, pepsin in the gastric juice and trypsin, chymotrypsin, and elastase secreted into the small intestine by the pancreas. Exopeptidases catalyze the hydrolysis of peptide bonds, one at a time, fi"om the ends of polypeptides. Carboxypeptidases, secreted in the pancreatic juice, release amino acids from rhe free carboxyl terminal, and aminopeptidases, secreted by the intestinal mucosal cells, release amino acids from the amino terminal. Dipeptides, which are not substrates for exopeptidases, are hydrolyzed in the brush border of intestinal mucosal cells by dipeptidases. 

The proteases are secreted as inactive zymogens the active site of the enzyme is masked by a small region of its peptide chain, which is removed by hydrolysis of a specific peptide bond. Pepsinogen is activated to pepsin by gastric acid and by activated pepsin (autocatalysis). In the small intestine, trypsinogen, the precursor of trypsin, is activated by enteropeptidase, which is secreted by the duodenal epithelial cells trypsin can then activate chymotrypsinogen to chymotrypsin, proelas-tase to elastase, procarboxypeptidase to carboxypepti-dase, and proaminopeptidase to aminopeptidase. 

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