378 ENZYMES 



THE ISOLATION OF ZYMASE. 



The following is the method pursued by Buchner in isolat- 

 ing zymase from Saccharomyces. One kilogram of com- 

 pressed yeast is mixed with 250 grams of the infusorial earth 

 known as kieselguhr and a quantity of fine quartz sand. The 

 mixture is ground in a mortar until the microscope shows the 

 majority of the yeast cells to be broken. To this paste-like 

 mixture are added 100 c.c. of water which is very thoroughly 

 stirred in ; the mass is then wrapped in a cloth, placed in a 

 press and gradually subjected to a very high pressure 

 Buchner used a pressure as high as 500 atmospheres the 

 liquid extracted being collected in a glass vessel. The resi- 

 due is then removed from the press, broken up, and again 

 mixed with 100 c.c. of water and subjected to pressure. The 

 extracts are united, shaken up with a little kieselguhr and 

 filtered. The filtrate contains the zymase, but in an impure 

 condition ; it may be purified by precipitating with alcohol 

 and dissolving the precipitate in water. The aqueous solu- 

 tion will not keep any great length of time, a character which 

 is shared with most other enzymes when in aqueous solution ; 

 this phenomenon is termed hysteresis. It may, however, be 

 preserved for a longer time but not indefinitely by drying 

 the extract under reduced pressure, the solid substance so ob- 

 tained being kept in a cold desiccator and dissolved in water 

 as occasion demands. 



In preparing extracts of yeast, it must be remembered that 

 the potency of the extracts depends upon the physiological 

 state of the yeast used. Thus, if brewers' yeast be taken from 

 the wort whilst fermentation is at its height, a high quality 

 zymase will be obtained ; if, however, fermentation of the wort 

 be over, the yeast taken from it will yield an extract of little 

 'or no fermenting power. 



GENERAL CONSIDERATIONS. 



The alcoholic fermentation of sugar by yeast may be repre- 

 sented by the equation : 



C 6 H 12 6 = 2 C0 2 + 2 C 2 H 6 



Recent investigations, however, have shown that the pheno- 

 menon is not quite so simple as this general statement indicates. 



