Proteolytically Effective Enzymes

Proteases effect the hydrolysis of peptide bonds. Some may also cause the scission of ester bonds or transpeptidization (exchange of peptide bonds). Some are produced from high-molecular-weight proteins by the elimination of amino acids. These high-molecular-weight proteins are called precursors or zymogens. 

A basic peptide is, e.g., eliminated from the amine end of the precursor pepsinogen (M = 42,500), and the enzyme pepsin (M = 35,500) is formed. The precursor trypsinogen (M = 23,700) converts into trypsin with a molecular weight of 15,100 under the action of enterokinase (ph 5.2-6.0) or trypsin itself in the presence of Ca ions pH 7-9). Chymotrypsin (M = 22,000) changes under the action of trypsin into a-chymotrypsin (M = 

Carboxypeptidase (M = 34,000) is produced from the zymogen procarboxy-peptidase (M = 95,000). 

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On the basis of this anti-proteolytic effect of sialic acids, a hypothetical model435 for the role of sialidase in clostridial infections is shown in Scheme 4. It is considered that the bacterial enzyme releases sialic acids from cell-surface glycoproteins of the infected tissue, which thereafter can be readily attacked by proteases. This cooperation between sialidase and protease may support the spreading of the bacteria. Acylneuraminate pyruvate-lyase, also shown in this model, degrades sialic acids for energy supply, and growth, of the bacteria. 

A classic text, directed at the food sciences, covering the fundamental principles of enzymology. Chapters covering enzyme purification, pH effects, temperature effects, enzyme inhibitors, and the proteolytic enzymes are particularly relevant to this unit. 

In such a manner, the activity of different proteolytic enzymes has been estimated. Since the products of proteolytic cleavage can exhibit higher catalytic waves than those of the native proteins, the proteolytic effect can be investigated polarographically. Larger protein molecules can be precipitated with sulphosalicyclic acid. The polarographic analysis of these filtrates corresponds to the content of proteolytic products mainly. 

Although the cytoplasm of the cell and the fluids that bathe the cells have a pH that is carefully controlled so that it remains at about pH 7, there are environments within the body in which enzymes must function at a pH far from 7. Protein sequences have evolved that can maintain the proper three-dimensional structure under extreme conditions of pH. For instance, the pH of the stomach is approximately 2 as a result of the secretion of hydrochloric acid by specialized cells of the stomach lining. The proteolytic digestive enzyme pepsin must effectively degrade proteins at this extreme pH. In the case of pepsin the enzyme has evolved in such a way that it can maintain a stable tertiary structure at a pH of 2 and is catalytically most active in the hydrolysis of peptides that have been denatured by very low pH. Thus pepsin has a pH optimum of 2. 

The pathophysiology of immune complex reactions occurs in several stages formation of immune complexes in antigen excess, deposition of complexes in tissue, activation of complement followed by attraction at the site of plynuclear neutrophils, and liberation in tissue of proteolytic lysosomal enzymes and inflammatory cationic proteins. The importance of concomitant increase in vascular permeability for the deposition of immune complexes has been shown in vivo by the preventive effect of antihistaminic and antiserotonin drugs on the development of serum sickness to horse antidiphteric serum (Kniker et al. 1971). 

Exogenous enzymes are those that are added by the brewer rather than those that occur naturally from the malted cereals and yeast. Enzymes are available that exhibit proteolytic, cytolytic (plant cell wall material) and carbohydrase activity. Cost-effective enzyme preparations are not in general pure enzymes, however, a blend is often an advantage, enabling more than one activity to occur. 

Recent reports by Yeh and Kim that CoA activation of acetyl-CoA carboxylase results in lowering the Km for acetyl-CoA should be considered as one possible mechanism for affecting the activity of carboxylase (133, 134). Purification of the carboxylase progressively lowers the Km for acetyl-CoA to about 10 to 25 /xAf. This suggests that proteolytic effects or the removal of some inhibitory molecule from the native enzyme occur during the purification. However, at present, the reason for the decrease in the Km for acetyl-CoA during the purification of carboxylase remains obscure. 

The first intermediate—7r-chymotrypsin—displays chymo-trypsin activity. Suggest proteolytic enzymes that might carry out these cleavage reactions effectively. 

A further controversy in the literature on xanthine oxidase preparations may be mentioned here. This concerns use of proteolytic enzymes in the purification procedure, a step first introduced by Ball (74), which undoubtedly increases yields of purified enzyme and generally simplifies the preparation. Despite suggestions to the contrary (70) it now seems (19, 58) that this treatment has little or no effect on the properties of the purified enzyme. 

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