Proteinases definition

Proteinases (Prt), again by definition, are responsible for the cleavage of peptide bonds, usually with a preference for particular types of side chain on the amino acid residues on one or the other or both sides of the scissile bond (Equation (7)). 

The normal form of PrP has been referred to as either PrP - for PrP-cellular or PrP-sen, which designates its sensitivity to proteinase K The abnormal form of PrP has been referred to as either PrP for PrP-scrapie or PrP-res, which designates its partial resistance to proteinase K Since the terms PrP-sen and PrP-res reflect a general biochemical definition rather than a disease-specific phenotype, they will be used throughout this discussion. 

By definition, all proteinases catalyze the hydrolytic degradation of peptide bonds of proteins (Fig. 3). In solution, the equilibrium lies so far to the right that the degradation and not the synthesis to large molecules is thermodynamically favored [20]. The shift toward hydrolysis can be attributed to the free-energy contribution from the ionization of the carboxyl and amino groups. 

The definition of the scope of the specificity of proteolytic enzymes with regard to the chemical configurations in the vicinity of the hydrolyzable peptide bond has necessarily been restricted to their peptidase activity in order that substrates of known chemical structure can be used. The familiar classification of proteinases on the basis of specificity towards peptides as model substrates, ss, 84, 85 meet rigorous testing on those rare... 

The end point of digestion is a matter of definition. Previously it was pointed out that the result of polysaccharide or protein digestion must involve a loss of specificity. In addition, the end product must be available to the cells. It is possible that the cells may further hydrolyze, and in that sense, digest, absorbed metabolites before assimilating or catabolizing them. The extracellular proteinases of the mammalian gut act on proteins to the extent of hydrolyzing them to a mixture composed of a high proportion of peptides compared to amino acids. Most of the work on intestinal... 

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