THE CHEMISTRY OF DIGESTION 



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(a) Proteolytic or protein-splitting enzymes, such as pepsin, give rise to a 

 hydrolytic cleavage of the protein molecule. 



(6) Lipolytic or fat-splitting enzymes, such as steapsin, cause a hydrolytic 

 cleavage of the fat molecule. 



(c) Amylolytic or starch-splitting enzymes, such as ptyalin, produce a hydro- 

 lytic cleavage of the starch molecule. 



(d) Inverting enzymes, such as maltase, split the disaccharides into monosac- 

 charides and the latter into simpler molecules. 



(e) Oxidizing enzymes, such as the oxidases of the tissues, which aid in internal 

 respiration. 



(/) Coagulating enzymes, such as rennin, which change soluble into insoluble 

 proteins. 



(g) Diaminizing enzymes, such as alanin, which split off an NH2 group from an 

 amino-acid as ammonia. 



In the following table are included some of the ferments with which 

 we are chiefly concerned at the present time, it being the custom 

 to designate them by the name of the substance upon which they act 

 and to affix the letters, ase. This suggestion (Duclaux) has been fol- 

 lowed in most instances, the only exceptions being those enzymes which 

 have been recognized for a long time, such as ptyalin, pepsin and trypsin. 



Although still incomplete, this enumeration proves very clearly 

 that almost every reaction necessitates the presence of a particular 

 enzyme. There can be only one reason for this, namely, that they are 

 specific in their action and cannot be employed interchangingly to 

 produce one and the same result. Thus, ptyalin changes starch into 

 maltose, but does not affect the fats and proteins, nor even the other 

 carbohydrates. Quite similarly, given a number of closely allied 



