466 ENZYMES 



other substances is, however, only really strongly marked in 

 connection with optically active substances. For, taking the 

 case of the fat-splitting enzymes or lipases, practically all esters 

 are broken up by pancreatic lipase, although the ease with 

 which the hydrolysis is effected may vary considerably in 

 different cases. 



CONDITIONING FACTORS. 



The rate of enzyme action is the resultant of various factors 

 the chief of which are temperature, reaction of medium, con- 

 centration of enzyme and of substrate, accumulation of end 

 products, paralysers, and radiation. The sensitivity of many 

 enzymes is so great that any one of these factors may 

 inhibit their activity, thus certain animal proteases are in- 

 active in an alkaline medium, pepsin for example ; or in 

 an acid medium, trypsin for example. On the other hand, 

 certain plant proteases are active in media irrespective of 

 its reaction. The appraisement of these factors, particularly 

 temperature and the reaction of the medium, is a matter of 

 some moment, for it is only when they are precisely ascertained 

 that the full value of the activity of an enzyme is available 

 in the laboratory and in industrial processes. They are, 

 however, often definable only within wide limits, since an 

 indisputably pure enzyme has yet to be obtained, and these 

 impurities may be effective in altering the value of the factor 

 in question. Willstatter * and his fellow-workers by special 

 methods of yeast cultivation and of preparation have isolated 

 an invertase (saccharase) possessed of high activity. The 

 preparation was effected by fractional autolysis of the yeast, 

 followed by dialysis, and purification was effected by adsorp- 

 tion on kaolin. The resultant enzyme was associated with 

 less impurity, was more stable, and was possessed of an 

 activity 28 per cent greater than any other previous pre-~ 

 paration. 



A general consideration of these factors follows ; a more 

 detailed account must be sought in manuals devoted to 



* Willstatter, Schneider, and Bamann : " Zeit. physiol. Chem.," 1925, 

 147, 248. 



