Peptidases activation

A proteolytic cascade occurs when one peptidase activates the next in a proteolytic pathway, and this in turn activates the next and so on. This is a mechanism to amplify the initial signal, because one peptidase molecule can activate many zymogen molecules. Examples of proteolytic cascades include blood coagulation, activation of digestive peptidases in the intestine, and apoptosis. 

The introduction of redox activity through a Co11 center in place of redox-inactive Zn11 can be revealing. Carboxypeptidase B (another Zn enzyme) and its Co-substituted derivative were oxidized by the active-site-selective m-chloroperbenzoic acid.1209 In the Co-substituted oxidized (Co111) enzyme there was a decrease in both the peptidase and the esterase activities, whereas in the zinc enzyme only the peptidase activity decreased. Oxidation of the native enzyme resulted in modification of a methionine residue instead. These studies indicate that the two metal ions impose different structural and functional properties on the active site, leading to differing reactivities of specific amino acid residues. Replacement of zinc(II) in the methyltransferase enzyme MT2-A by cobalt(II) yields an enzyme with enhanced activity, where spectroscopy also indicates coordination by two thiolates and two histidines, supported by EXAFS analysis of the zinc coordination sphere.1210... 

The same principle described above to monitor endo-peptidase activity was used by Matsuoka to monitor a ceramide glycanase... 

I.S. Han, N. Ramamurthy, J.H. Yun, U. Schaffer, M.E. Meyerhoff, and V.C. Yang, Selective monitoring of peptidase activities with synthetic polypeptide substrates and polyion-sensitive membrane electrode detection. FASEB J. 10, 1621-1626 (1996). 

M5. Messer, M., Anderson, C. M., and Townley, R. R. W., Peptidase activity of biopsies of the duodenal mucosa of children with and without coeliac disease. Clin. Chim. Acta 6, 768-775 (1961). 

Ajami, K., Abbott, C.A., McCaughan, G.W. and Gorrell, M.D. (2004) Dipeptidyl peptidase 9 has two forms, a broad distribution, cytoplasmic localization and DPIV-like peptidase activity. Biochimica et Biophysica Acta, 1679, 18-28. 

This is a 29-kDa protein that has NH 2-terminal sequence homology with elastase and cathepsin G. However, it contains glycine and not serine at the predicted catalytic site, and so lacks protease and peptidase activity. Purified azurocidin kills a range of organisms (e.g. E. coli, S.faecalis, and C. albicans) in vitro. It functions optimally at pH 5.5 and in conditions of low ionic strength. 

Walker GF, Langoth N, Bemkop-Schnurch A (2002) Peptidase activity on the surface of the porcine buccal mucosa. Int J Pharm 233 141-147... 

Garren K, and Repta A (1988) Buccal drug absorption Comparative levels of esterase and peptidase activities in rat and hamster buccal and intestinal homogenates. Int. J. Pharm. 48 189-194. 

B. Bauvois, J. Sanceau, J. Wietzerbin, Human U937 Cell Surface Peptidase Activities Characterization and Degradative Effect on Tumor Necrosis Factor-a , Eur. J. Immunol. 1992, 22, 923-930. 

Preliminary information useful in prodrug design has been obtained with amino acids attached to model aromatic amines. Thus, N-(naphthalen-2-yl) amides of amino acids (6.1, R=side chain of amino acid, R =H) proved to be of interest as test compounds to monitor peptidase activity such as ami-nopeptidase M (membrane alanyl aminopeptidase, microsomal aminopepti-dase, EC 3.4.11.2) [16][17], In the presence of purified rabbit kidney aminopeptidase M or human cerebrospinal fluid (CSF) aminopeptidase activity, the rate of hydrolysis decreased in the order Ala-> Leu->Arg->Glu-2-naphthyl-amide. Ala-2-naphthylamide, in particular, proved to be a good test compound, as its rate of hydrolysis was influenced by experimental conditions (preparation, inhibitors, etc.), as was the hydrolysis of a number of low-molecular-weight opioid peptides and circulating vasoactive peptides. 

A number of observations converge to indicate that much of plasma peptidase activity is due to aminopeptidases, with A-protection markedly increasing peptide stability in blood. Dipeptidyl-peptidase is another noteworthy peptidase in blood. In human plasma, some of the peptides showed very small tm values of only a few minutes, but a majority of f1/2 values were on the order of 10-30 min. 

M. Harada, HPLC Determination of Peptidase Activity toward Prohne-Containing Peptides , Anal. Chim. Acta 1997, 352, 179-185. 

Both the 26S proteasome and the RC hydrolyze all four nucleotide triphosphates, with ATP and CTP preferred over GTP and UTP [58]. Although ATP hydrolysis is required for conjugate degradation, the two processes are not strictly coupled. Complete inhibition of the peptidase activity of the 26S proteasome by calpain inhibitor I has little effect on the ATPase activity of the enzyme. The nucleotidase activities of the RC and the 26S proteasome closely resemble those of E. coli Lon protease, which is composed of identical subunits that possess both proteolytic and nucleotidase activities in the same polypeptide chain. Like the regulatory complex and 26S proteasome, Lon hydrolyzes all four ribonucleotide triphosphates, but not ADP or AMP [18]. 

Kopp, E., Dahlmann, B., and Kuehn, L. Reconstitution of hybrid proteasomes from purified PA700-20 S complexes and PA28alphabeta activator ultrastructure and peptidase activities. JMol Biol 2001, 313, 465-71. 

Low expression levels and the lability of the HslVU complex make work with proteins from wild-type strains difficult. Gratifyingly, the active protease can be reconstituted in vitro from over-expressed and purified components (Rohrwild et al. 1996). It requires ATP for the degradation of folded substrates and ATP or some of its analogs for the purification of small chromogenic peptides. As expected, ATP-hydrolysis and proteolysis activities are mutually dependent (Seol et al. 1997). In addition, the peptidase activity was found to depend in complex ways on the presence of various cations, especially K in the buffers (Huang and Goldberg 1997). 

The 20S proteasome can exist not only as a core of 26S, but also as a separate population that cannot degrade ubiquitinated proteins. However, the 20S proteasome by itself has chymotrypsin-like, trypsin-like, and postglutamyl peptidase activities which cleave after hydrophobic, basic, and acidic residues, respectively. The peptide-hydrolyzing activity of the 20S proteasome can be modulated by an IIS regulatory cap. °°... 

K (peptidase activity) = 0.018 pM IC50 (epoxide hydrolase activity) = 0.2 pM... 

Pentene complexes with silver, 12 336 Peptidase, activity, [Tp ]ZnOH complexes, relevance, 42 367-370... 

Let us see where this scheme may bring us, and for this purpose refer to Figure 4.7. This shows a small library of oligopeptides, where one (or more) of these products, indicated in the figure with an asterisk, is endowed with peptidase activity. These peptides then, under the reaction conditions, can catalyze fragment condensation in a specific way - for example of those peptides with a terminal aromatic residue. Following the first condensation step, the catalytic center is inserted into a longer polypeptide, with retention of the catalytic activity. 

As some of the newer drugs such as hormones, growth factors, and cytokines now being produced are peptides and certain toxins are also peptides or proteins, the role of peptidases may be important. Peptidases are especially active in the lumen of the gut, and consequently many such drugs are administered intravenously. Also some natural protein toxins may bypass the gut by via bites or stings into tissue. However, peptidase activity is also found in blood and other tissues. Peptidases are also important in the further metabolism of glutathione conjugates (see below). 

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