48 GENERAL AND PHYSICO-CHEMICAL. 



Of the above mentioned enzymotic reactions the hydrolytic cleavage 

 processes have been best studied, and the general properties of the 

 enzymes which will be given apply chiefly to the hydrolytically splitting 

 enzymes. Among these the following are to be mentioned especially: 



1. Enzymes which split fats and other esters with the formation of 

 the corresponding alcohol and acid. They are called Upases or esterases. 



2. Enzymes which split complex carbohydrates with the formation 

 of simpler ones. To these belong: 



a. Disaccharide splitting enzymes for instance saccharase (invertase, 

 invertin), maltase, lactase which act upon the corresponding disaccharide 

 saccharose (cane-sugar) maltose and lactose (milk sugar); 



b. Polysaccharide splitting enzymes such as amylase, ptyaUn. The 

 name diastase is often used to designate all the enzymes of this group. 

 In close relation to these enzymes stand the glucoside splitting enzymes 

 which occur especially in higher plants and the best known of which is 

 amygdalase (emulsiri) occurring in the almond. 



3. Enzymes which act upon the proteins or their related cleavage 

 products. Of these we have : 



a. Peptidases and erepsin which split polypeptides or peptones; 



b. Proteases which act upon proteins as substrate (pepsin, trypsin, 

 autolytic enzymes). 



Among the hydrolytic enzymes of the animal kingdom we also 

 include the arginase, which splits arginine into urea and ornithin and the 

 histozym, which splits hippuric acid. The two following groups also 

 belong here, namely, the nucleases which split nucleic acids and which 

 will be discussed in Chapter II, and the coagulating enzymes, rennin 

 and thrombin, which are probably active as proteases. The deamidizing 

 enzymes which split off the NH2 group from amino combinations are, 

 at least in certain cases, to be classed as hydrolytic enzymes. This is 

 for example the case with the adenase and guanase which splits off ammonia 

 from the two bodies adenine and guanine converting them into hypoxan- 

 thine and xanthine respectively. The urease which splits urea also belongs 

 to this group. 



General Properties of the Enzymes. When possible we make use 

 of watery solutions of enzymes in experimentation. In case they are 

 insoluble in water (certain Upases) we use them in the form of more or 

 less purified powders or together with the tissue where they are formed. 

 We have no general method for preparing enzyme solutions. In certain 

 cases they are contained in secretions (gastric and pancreatic enzymes) ; 

 in others they are prepared from the cells by crushing and pressing out 

 the cell juice (zymase, organ enzymes), and finally, most enzymes can 

 be extracted from the cells with water or glycerin, and as this last gives 

 permanent solutions it has found great use as an extraction medium. 



