112 PHYSIOLOGICAL ACTIVITIES 



dextrorotatory one which is attacked. No single enzyme 

 attacks both. This probably means that the structure of 

 the enzyme corresponds to that of the substrate, "fits it as 

 a key fits a lock," as Emil Fischer says. 



The production of enzymes is by no means restricted to 

 bacteria since all kinds of living cells that have been inves- 

 tigated have been shown to produce them and presumably 

 all living cells do. Hence the number of different kinds of 

 enzymes and of substances acted upon is practically unlim- 

 ited. Nevertheless they may be grouped into a compara- 

 tively few classes based on the general character of the 

 change brought about by them. 



I. Class 1 is the so-called "splitting" enzymes whose 

 action is for the most part hydrolytic, that is, the substance 

 takes up water and then splits into compounds that were ap- 

 parently constituents of the original molecule. As examples 

 may be mentioned diastase, the enzyme first discovered, which 

 changes starch into a malt-sugar, hence is more commonly 

 called amylase^ (starch-splitting enzyme); invertase,^ which 

 splits cane-sugar into dextrose and levulose: C12H22O11 -|- 

 H2O = C6H12O6 + C6H12O6. Lipase^ or a fat-splitting 

 enzyme, which decomposes fat into glycerin and fatty acid: 



Fat Glycerin Fatty acid 



C3H6(OCnH2n-iO)3 + SHjO = C3Hb(OH)3 -|- SCnHjnOj. 



Proteases, which split up proteins into proteoses and pep- 

 tones. 



Other classes of "splitting enzymes" break up the prod- 

 ucts of complex protein decomposition, such as proteoses, 

 peptones and amino-acids. A variety of the "splitting 

 enzymes" is the group of 



" Coagulases" or coagulating enzymes as the rennet (lab, 

 chymosin) which curdles milk; fibrin ferment (thrombin, 

 thrombase) which causes the coagulation of blood. These 

 apparently act by splitting up a substance in the fluids 

 mentioned, after which splitting one of the new products 

 formed combines with other compounds present (usually a 



'■ It will be noted that the names of enzymes (except some of those first 

 discovered) terminate in ase which is usually added to the stem of the name 

 of the substance acted on, though sometimes to a word which indicates the 

 substance formed by the action, as lactaddase, alcoholase. 



