Protein proteinase activity

Proteinase-activated recqrtors (PARs) are a unique family of G-protein-coupled receptors (GPCRs) that are activated in response to serine proteinases. There are four PAR family members PAR-1 through to PAR-4. PAR-1 and PAR-3 respond to thrombin, PAR-2 responds to trypsin, whilst PAR-4 is sensitive to both thrombin- and trypsin-related proteinases. 

In an earlier report (J>), the decay of healthy yam tubers during storage was shown to be a result of catabolism of its proteins by an active a-glutamyl transpeptidase. There is also some alkaline proteolytic activity in the yam tuber (6), but little information is available on individual enzymes of the purine degradative pathway and on the properties of an alkaline proteinase that may function in yams during storage. This report describes the interrelation of five enzymes of ureide metabolism in fresh and stored yams, the release of ammonia in vitro by three of the enzymes that may provide an environment for alkaline proteinase activity in vivo, and the in vitro properties of an... 

Table 4. Substrate Specificity of Yam Tuber Alkaline Proteinase (Activity mg protein hydrolyzed)/10 mg enzyme/2hr).

Normally, thrombin is present in the blood as an inactive proenzyme (see p. 270). Prothrombin is activated in two different ways, both of which represent cascades of enzymatic reactions in which inactive proenzymes (zymogens, symbol circle) are proteolytically converted into active proteinases (symbol sector of a circle). The proteinases activate the next proenzyme in turn, and so on. Several steps in the cascade require additional protein factors (factors 111, Va and Villa) as well as anionic phospholipids (PL see below) and Ca "" ions. Both pathways are activated by injuries to the vessel wall. 

Huang, C., Ma, W. Y.,Ryan, C. A., Dong,Z. (1997). Proteinase inhibitors I and II from potatoes speeifieally bloek UV-indueed activator protein-1 activation through a pathway that is independent of extracellular signal-regulated kinases, c-Jun N-terminal kinases, and P38 kinase. Proc. Natl. Acad. Sci. U. S. A., 94, 11957-11962. 

Figure B3.1.2 Native discontinuous polyacrylamide gels activity stained for proteinases. (A) Gel stained with Coomassie brilliant blue for total protein. (B) Gel assayed for proteinase activity using casein as a substrate. Samples are enzyme extracts of hepatopancreas from four shrimp species. Lane 1, molecular weight markers Lane 2, Rcaliforniensis Lane 3 R vannamei Lane 4, Rpaulensis, Lane 5, P. schmitti.

Another possible mechanism for kallikrein action in physiology and pathobiology is the activation of proteinase-activated receptors (PARs). PAR is a recently described family of G-protein-coupled receptors with seven transmembrane domains that are stimulated by cleavage of their N-termini by a serine protease rather than by ligand-receptor interaction [184-186]. Four PARs have been identified so far, of which PARI, PAR3,... 

We have shown above, although in a very qualitative way, that various NMR evidence seems to indicate that two peculiar features of SSI, namely dimeric structure and wide inhibitory activity, which are rather unusual for protein proteinase inhibitors, are actually closely related. The molecular assembly of the SSI subunit can be conceptually divided into two subdomains having a similar topology domain I, which is located at the N-... 

Oxidative Regulation of Proteinase Activities—Protein Inhibitors Balance. 213... 

It is helpful in the effort to understand activation complexes to consider complex formation, the reactions that occur in the complexes, and the demise of the complexes as proceeding in a sequence. First, a reversible, noncovalent association of proteinase, cofactor protein (strictly, activated cofactor protein), proteinase precursor, and membrane surface occurs to form the activation complex. This spontaneous association occurs as the result of complementary interaction sites on the protein molecules, e.g., the binding sites between proteinase and protein substrate, proteinase and cofactor protein, substrate and cofactor protein, and all three proteins with the membrane surface. Tissue factor normally exists as an integral membrane protein and is always associated with the membranes of cells in the vessel wall. The same processes are involved in the anticoagulant subsystem and, with a different surface, fibrin in the fibrinolytic system as well. 

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