Specific Proteolytic Enzymes

Homogenates of the muscle layer of rat small intestine inactivate ornithine aminotransferase, with the catalytic activity being lost more 

Whatever the true function of group-specific proteinases, it seems reasonable that they play a significant role in intracellular enzyme catabolism. Further investigations should clarify this role, as well as establish whether a wide range of such proteinases occurs in tissues. 

All intracellular enzymes in mammalian cells are degraded by a pathway which produces amino acids. To date no intermediates in the sequence have been described, and information on the intracellular localization of the pathway and on the interplay between various sub-cellular fractions is very sparse. Nevertheless, measurement of half-lives of many enzymes has been made, especially those present in the liver cytosol, and a general picture is appearing as to why some enzymes are stable in vivo and others extremely unstable. 

The contribution of enzyme degradation to the various adaptation responses seen in mammalian tissues is becoming clear. Although changes in enzyme content are usually slower than those caused by allosteric ligands, they are extremely important for the long-term modifications which enable a cell to carry out its major functions in a changing environment. 

Anfinsen, C. B., and Scheraga, H. A., 1975, Experimental and theoretical aspects of protein folding, Adv. Protein Chem. 29 205. 

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The granules contain two types of proteins that result in death. First, compounds that produce holes (pores) in the membrane of the cells these are the proteins, perforin and granulysin. Both insert into the membrane to produce the pores. These were once considered to result in death by lysis (i.e. exchange of ions with extracellular space and entry of water into the cell). However, it is now considered that the role of the pores is to enable enzymes in the granules, known as granzymes, to enter the cell. These granzymes contain proteolytic enzymes. They result in death of the cell by proteolysis but, more importantly, activation of specific proteolytic enzymes, known as caspases. These enzymes initiate reactions that result in programmed cell death , i.e. apoptosis (Chapter 20). 

Highly specific proteolytic enzymes cleave a single peptide bond in a naturally occurring substrate. These proteases appear to be Integral parts of many biologic processes and may be contrasted with less specific proteases Isolated from the gastrointestinal tract. 

After the introduction of pronase E, other more or less nonsubstrate-specific proteolytic enzymes have been applied to assist Se speciation. Most of them were derived from DNA/RNA clean-up protocols. The new enzymes (subtilisin from Bacillus licheniformis, also named protease VIII, EC 3.4.21.14 proteinase K from Tritirachium album, EC 3.4.21.64 the crude Novo Nordisk product of Flavourzyme from Aspergillus oryzae) proved to be capable of extracting Se with varying yields and chromatographic recovery of Se species. It is important to highlight that the latter parameter also depends on the instrumentation available. In this regard, different recovery values for the same samples reported by independent research groups do not necessarily indicate successful or unsuccessful sample preparation. Similarly, extraction efficiency (defined as the ratio of extracted Se to total Se in the sample) cannot be used as such for comparison purposes because sample preparation may include some extra steps, for example, TCA precipitation or ultrafiltration, which may reduce this value even by 10-20 percent. 

Proteolytic enzymes have long been used to produce protein hydrolysates for use in soups, bouillon, soy sauce, tamari sauce, etc. Recent interest in producing large polypeptides of controlled size having improved solubility and functional properties for use in the food industry has led to investigation of highly specific proteolytic enzymes for that purpose (34, 35). 

Proteins and peptides are accessible to enzymatic action due to the susceptibility of specific amino acid sequences, and such proteolysis is a naturally occurring metabolic process in vivo. Degradation pathways generally involve hydrolysis of peptide bonds by a variety of exopeptidases and endopeptidases, and the specific proteolytic enzymes associated with non-invasive routes of administration have been identified in some detail. Enzymatic activity varies depending on the delivery route and a qualitative rank ordering is shown in Table 1. Since a significant portion of dietary protein consumed by humans is assimilated by means... 

Although a variety of (specific) proteolytic enzymes ate available, tiypsin is applied in most studies. Trypsin cleaves the protein at the C-terminal side of Lys or Arg, unless the next C-terminal amino acid is Pro. Other missed cleavage sites occur as well. Tryptic peptides are often indicated with Tx, where x is the number of the tryptic peptide, counted from the A-terminal side of the protein. The reaction can be performed in various ways homogeneous digestion, with tiypsin immobilized on beads, or by means of a trypsin immobilized enzyme reaction (IMER). 

After the removal of the signal peptide, a peptide segment referred to as the C chain is removed by a specific proteolytic enzyme. Two disulfide bonds are also formed during insulin s posttranslational processing. 

The biodegradability of chitin and chitosan is mainly due to their susceptibility to enzymatic hydrolysis by lysozyme, a non-specific proteolytic enzyme present in all tissues of the human body. Lipase, an enzyme present in the saliva and in human gastric and pancreatic fluids, can also degrade chitosan [142]. The products of the enzymatic degradation of chitosan are non-toxic. The degree of acetylation, the molecular weight, the pH and even the method of preparation of chitosan affect biodegradation. 

Dissolution of preexisting collagen fibers in the immediate proximity of neoplastic cells is a well-recognized feature of active invasive growths. This has led many to postulate that tumor cells release collagenase, a specific proteolytic enzyme found in both mammalian and bacterial cells. Extracts of various animal and human tumors exhibit enhanced collagenase activity (104,131,270, 310, 319). 

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