CHAPTER VIII 



PROTEOLYTIC ENZYMES 



Putrefaction of the remains of dead animals and plants in 

 natural environments is due in part to autolysis, i.e. to dis- 

 integration of cellular components by the organism's own 

 enzymes [27], and in part to the activities of the mixed 

 population of micro-organisms which rapidly becomes 

 established in such conditions. Because of their insolubility 

 or molecular size, many cellular materials must be degraded 

 to simpler substances before they can be utilized by micro- 

 organisms as sources of carbon, nitrogen and energy. De- 

 gradation may be accomplished either by enzymes present 

 in the cell wall of the micro-organism, in which case the 

 organism must itself come into physical contact with the 

 substrate (e.g. the digestion of cellulose by species of Cyto- 

 phaga), or by extracellular enzymes produced by the micro- 

 organism yet acting independently of the parent cell. One 

 group of extracellular enzymes especially important in 

 putrefaction is the proteases, enzymes which hydrolyse 

 peptide bonds and thus make available the amino-acid con- 

 stituents of proteins. 



For several years bacteriologists have used physical mani- 

 festations of proteolytic activity in the classification and 

 identification of micro-organisms, e.g. the liquefaction of 

 gelatin or the clotting and digestion of milk. Moreover, the 

 unwelcome effects of some pathogenic bacteria are now 

 known to be due to extracellular toxins which possess en- 

 zymic activity against certain proteins in the susceptible 

 host. Mainly because of the influence of industry and medi- 

 cine, the proteolytic activity of bacteria has been studied 

 almost exclusively in terms of natural substrates such as 

 casein, collagen (or gelatin) and fibrin, and more from the 

 viewpoint of the bacteriologist rather than the biochemist. 

 On the other hand, there have been considerable advances 

 in knowledge with regard to animal proteases, several of 



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