CHANGES IN EXPRESSED YEAST JUICE 471 



Alcohol has long been in use as a precipitant for isolating 

 enzymes. Since, however, prolonged contact with alcohol must be 

 avoided with the more stable enzymes (e.g., invertase), caution is 

 all the more necessary in the case of the more sensitive enzyme 

 of alcoholic fermentation. According to ALBERT and BUCH- 

 NER (III.)> the whole of the fermentative enzyme can be recovered, 

 without loes, when the expressed yeast juice is treated with at 

 least twelve times its own volume of absolute alcohol or preferably 

 with a mixture of 800 c.c. of absolute alcohol and 400 c.c. of ether 

 per 100 c.c. of yeast juice the liquid being aspirated off' as rapidly 

 as possible, and the precipitate washed with ether and dried over 

 sulphuric acid in a vacuum desiccator. The precipitated fermenta- 

 tive enzyme is completely soluble in water containing 2.520 per 

 cent, of glycerin. Jn order to retain the fermentative power of 

 the precipitate intact, the simplest method is to suspend it in the 

 solvent. The portion dissolved by the aid of water and glycerin 

 can be reprecipitated with ether-alcohol, without greatly impair- 

 ing the efficiency of the preparation. The proteids are, of course, 

 the chief constituent of the precipitates, so that only an insignifi- 

 cant proportion of the total weight of the precipitate consists of 

 fermentative enzyme. 



When methyl alcohol is used as precipitant (see p. 242, vol. ii.), 

 the fermentative power of the precipitate is, strange to say, entirely 

 destroyed. Ether by itself, as first pointed out by WILL (XXXV.), 

 causes the production of a jelly, which is rich in the fermentative 

 enzyme. Favourable results have also been obtained with acetone 

 for precipitating the proteids of yeast juice. At first the present 

 writer made the mistake of using an insufficient quantity of the 

 acetone, at least a tenfold volume being requisite for throwing 

 down the whole of the fermentative enzyme. According to the 

 later researches of BUCHNER and ANTONI (II.) the precipitates 

 obtained with smaller quantities of acetone are deficient in the 

 phosphoric acid compounds essential to successful fermentation, 

 whilst increasing the quantity of acetone causes an increased pro- 

 portion of saline matter to be thrown down in the precipitate. 



In addition to the foregoing reagents, BUCHNER (X.) employed 

 ammonium sulphate and also cholesterin, according to the method 

 of Briicke, a,s a precipitant of the fermentative enzyme of yeast 

 juice. In the former case, however, no fermentation could be 

 observed at all, and merely traces in the latter. AHRENS (I.) 

 used zinc sulphate and alcohol, and WROBLEWSKI (IV.) ammonium 

 sulphate, for the same purpose, but neither of them tested the 

 fermentative power of the precipitates. Wroblewski employed 

 partial precipitation, and obtained five precipitates with an equal 

 number of filtrates. In this partial precipitation the proteids 

 which, as already mentioned (p. 462) are coagulated at different 

 temperatures are thrown down in an incomplete manner. 

 Finally, K. GREEN (III.) also confirmed the fact that the fermen- 



