156 PHYSIOLOGY OF ALIMENTATION. 



the products of the inversion are removed does the catalysis 

 go to an end. 



The optimal temperature for sucrase is given by KJELDAHL 

 as 52 C. for a preparation obtained from yeast. EFFRONT 

 states that at C. the activity of sucrase is practically nil, 

 rises slowly up to 30 C. to increase more rapidly up to 50 C., 

 after which it falls again. At a temperature of 65 C. the 

 ferment is rapidly destroyed. External conditions modify 

 very markedly the points at which the optimal temperature 

 and the maximal temperature are attained. 1 While a dilute 

 solution of sucrase may be kept at 52 C. for an hour without 

 losing its fermentative activity, more concentrated solutions 

 suffer considerably if kept at the same temperature for even 

 shorter periods of time. At 65 C. a concentrated solution 

 of sucrase is entirely destroyed within an hour, while a more 

 dilute solution bears this treatment with only a partial loss 

 of its activity. Besides these variations in optimal and maxi- 

 mal temperatures in the same preparation of sucrase under 

 different external conditions, marked differences are also 

 found between sucrase preparations obtained from different 

 sources. The various sucrase preparations differ, for example, 

 in their optimal and maximal temperatures, in their resistance 

 to chemical and physical agents, etc. On this ground certain 

 investigators have tried to establish the existence of varieties 

 of sucrase. The same can be said of this ferment, however, 

 which has been said of others, that when obtained from dif- 

 ferent sources the impurities accompanying the preparations 

 are not the same. Preparations of sucrase differ, therefore, 

 not because of specific differences in the sucrase itself, but 

 because of specific differences in the impurities accompanying 

 the sucrase. Certain of these act more deleteriously upon the 

 enzyme than others, and we get in consequence the long line 

 of differences which authors have claimed exist in the sucrases 

 themselves. 



1 By maximal temperature is meant the temperature at which the 

 fermentative reaction no longer takes place. 



