Proteolysis proteolytic enzyme activation

Proteolytic bacteria were present in relatively high numbers (10 /g of digetsa) in sheep fed on Calliandra leaves (McSweeney et al. 1999). The changes in the activities of proteolytic bacteria and the protease enzyme by tannins conld mediate nitrogen metabolism in the rumen (Tanner et al. 1994). A reduction in proteolysis might be attributed to the direct effects of CT on microbial proteolytic enzyme activity or... 

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). 

The proteolysis of cellulases has been previously investigated. Nakayama et al. (14) found that mild proteolysis of endoglucanase from T. reesei by a protease prepared from the same fungus resulted in cellulase enzymes which still possessed cellulolytic activity. Earlier, Eriksson and Petterson (24) investigated the effect of various proteolytic enzymes on the cellulase activities on Penicillium notatum. They found that different proteases affected enzyme activities to different degrees. 

In the diet, vitamin B12 is bound to proteins. Although some release of protein-bound vitamin B12 begins in the mouth, most of the release occurs in the stomach on exposure of food to gastric acid (HC1) and the proteolytic enzyme pepsin. For this reason, either hypo-chlorhydria (abnormally low concentration of HC1 in gastric fluid) or achlorhydria (the absence of HC1 in gastric fluid) may decrease the availability of dietary vitamin B12 for absorption by preventing the activation of pepsinogen to pepsin, the principal enzyme responsible for proteolysis in the stomach. Achlorhydric patients with adequate production of IF may have low normal or subnormal serum B12 concentrations because of failure to liberate B12 bound to food. 

Proteolysis plays a central role in apoptosis, as it does in the control of the cell cycle (Chapter 12). Apoptotic signals activate a cascade of proteolytic enzymes which degrade... 

Thrombin is a proteolytic enzyme and has a remarkable similarity in its overall three-dimensional structure to the digestive serine proteases, trypsin, and chymotrypsin [11-13]. Trypsin and thrombin share a common primary specificity for proteolysis next to arginine or lysine residues. Structural data of thrombin and trypsin have demonstrated strong resemblance in their substrate sites, and many small organic inhibitors are comparably active against both the enzymes [14,15]. For this reason, no or low inhibition of trypsin is viewed as a required condition for a compoimd to be a successful orally bioavailable thrombin inhibitor [16]. 

Examination of the action of proteolytic enzymes on native proteins (or biologically active peptides) can yield two important types of information. First, determination of the susceptibility of particular bonds in a protein substrate offers a means for evaluation of certain features of the conformation of the protein (Linderstr0m-Lang, 1952 Mihalyi and Harrington, 1959). Second, proteolysis can serve as an important method for modification of the covalent structure of biologically active proteins (Anfinsen and Redfield, 1956). 

Protein digestion begins in the stomach, where the acidic environment favors protein denaturation. Denatured proteins are more accessible as substrates for proteolysis than are native proteins. The primary proteolytic enzyme of the stomach is pepsin, a nonspecific protease that, remarkably, is maximally active at pH 2. Thus, pepsin can be active in the highly acidic environment of the stomach, even though other proteins undergo denaturation there. 

Proteolysis. The polarographic proof of proteolysis and the estimation of some proteolytic enzymes by means of the increase of the polarographic activity of hydrolysed proteins are described on p. 267. In this part, we should mention another method of following the proteolytic activity. Some polypeptides yield high polarographic catalytic waves in the Brdicka cobalt(III) solution (see p. 265). However, the products of their hydrolysis are polarographically much less active in cobalt (III) solution (see p. 265). In such a manner, the influence of serum of pregnant women on the hydrolysis of protein pituitary extract and on oxytocin and vasopressin was measured [178,179]. 

T15. Taylor, W. H., Studies on gastric proteolysis. 2. The nature of the enzyme-substrate interaction responsible for gastric proteolytic pH-activity curves with two maxima. Biochem. J. 71, 373-383 (1 9). 

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... 

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