Peptidases extracellular

Extracellular peptidases are relatively easy to isolate and are, therefore, well-studied. In higher organisms, they perform a variety of different functions such as food digestion, control of blood pressure and blood clotting, and complement activation, among others. A few examples are compiled in Table 2.2. 

Table 2.2. Location and Function of Some Extracellular Peptidases...

The isolation and investigation of intracellular tissue peptidases is more difficult than that of extracellular peptidases, and, as a result, less is known about such peptidases. Illustrative examples of peptidases with their intracellular localization are presented in Table 2.3 [7a],... 

This enzyme [EC 3.4.24.27], also known as Bacillus ther-moproteolyticus neutral proteinase, is a thermostable extracellular metalloendopeptidase containing zinc and four calcium ions. A member of the peptidase family M4, this enzyme catalyzes the hydrolysis of peptide bonds with a preference for Xaa—Leu > Xaa—Phe. 

Extracellular cleavage of procollagen molecules After their release, the procollagen molecules are cleaved by N- and C-pro-collagen peptidases, which remove the terminal propeptides, releasing triple-helical collagen molecules. 

Penicillium caseicolum produces an extracellular aspartyl proteinase and a metalloproteinase with properties very similar to those of the extracellular enzymes produced by P roqueforti (Trieu-Cout and Gripon 1981 Trieu-Cout et al. 1982). Breakdown of casein in mold-ripened cheese results from the synergistic action of rennet and the proteases of lactic streptococci and penicillia (Desmazeaud and Gripon 1977). Peptidases of both lactic acid bacteria and penicillia contribute to formation of free amino acid and nonprotein nitrogen (Gripon et al. 1977). 

Law, B. A. 1979B. Extracellular peptidases in Group N streptococci used as cheese starters. J. Appl. Bacterial 46, 455-463. 

Within the extracellular space two procollagen peptidases act to cleave a 35-kDa peptide from the C terminus631 and a 20-kDa peptide from the N-terminal end of each of the three chains of the secreted procollagen. The amino acid composition of the peptides removed is quite unlike that of the remaining collagen monomer (also called tropocollagen) which contains one-third glycine and much proline. 

Hydrolytic reactions are catalyzed by extracellular hydrolases and mineral surfaces (Chrost, 1990 Hoffman, 1990). For enzymatic reactions, a defined substrate or moiety must match the catalytic site of a specific enzyme. The most studied examples in aquatic systems are glycosidases, peptidases, and phosphatases (Munster and De Hann, 1998 see Chapter 13). In general, hydrolytic reactions break the relatively labile C—N and C—O bonds that link monomers, generating lower molecular weight products more suitable for microbial consumption. 

Christie A, Butler M (1994), Glutamine-based dipeptides are utilized in mammalian cell culture by extracellular hydrolysis catalyzed by a specific peptidase, J. Biotechnol. 37 277-290. 

Cat B is an abundant and ubiquitously expressed cysteine peptidase of the papain family and makes up a major fraction of lysosomal enzymes that is capable of degrading components of the extracellular matrix in various diseases [30-32]. Cat B is also a prognostic marker for several types of cancer [33], and increased expression and secretion of cat B has been shown to be involved in the migration and invasion of various tumours [34—36], The precise role of cat B in solid tumours is not fully understood, but it has been proposed to participate, along with other cysteine cathepsins, in metastasis, angiogenesis, and tumour progression [37], Indeed, cat B inhibitors reduce both tumour cell motility and invasiveness in vitro [38], Recently, metal complexes based on rhenium, gold and palladium were shown to be effective inhibitors of cat B [39-44],... 

The procollagen molecule is secreted from the cell, and the extension propeptides are excised by two specific procollagen peptidases to form the tropocollagen molecule. The removal of the peptides (Mr = 20,000 and 35,000) allows the tropocollagen molecules to self-assemble to form fibrils. This assembly is regulated to some extent by the cells and by other extracellular components to produce the wide variety of structures found in collagen fibers. 

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