58 PHYSIOLOGY OF YEASTS 



General Considerations of Enzymes in Yeasts 



The study of enzymes has been much advanced by Buchner who 

 developed a procedure which allowed the extraction of the juice. Before 

 this method was known, it was difficult to extract these enzymes which, 

 as is generally known, are not always susceptible to passage through a 

 membrane. They may remain on the interior of the cell and act there. 

 Buchner's method, which consists in searching the yeast juice for the en- 

 zymes, is the only one which offers any guarantee of success. 



Preparation of Yeast Juice 



It is, then, by the preparation of yeast juice that we must take up 

 the study of the enzymes. In 1897, Buchner was able to isolate the 

 enzyme which produced the alcoholic fementation by decomposing sugar 

 into carbonic acid and alcohol. This he called zymase or alcoholase. He 

 did this according to the following procedure. He ground up 1000 grams 

 of yeast after careful washing and drying. This was a difficult proce- 

 dure on account of the elasticity of the yeast cells, but in order to ac- 

 complish this, it was necessary to mix the cells with fine sand and rotten 

 stone. With the aid of a heavy iron pestle, he triturated the yeast, 

 previously dehydrated, with 1000 grams of quartz sand and 250 grams 

 of rotten stone in the form of a thick paste. This was expressed in a 

 hydraulic press under a pressure of 300 to 500 atmospheres. From 400 

 to 500 c.c of the yeast juice were thus obtained. 



The extract thus obtained is a brownish liquid with somewhat the 

 odor of fresh yeast little or not at all dialyzable. Heating to 40-50 

 causes a precipitation of albumin and the liquid loses its fermenting 

 power. It contains, along with a certain quantity of albumin (4.15 per 

 cent), the products of tryptic digestion (albumoses, peptones, tyrosine), 

 lecithin, a phosphorus compound (nucleic acid), 2 per cent of ash and 

 the products of fermentation (0.53 per cent of alcohol, 0.07 per cent 

 carbon dioxide, 0.096 per cent of glycerol, and 0.016 per cent of suc- 

 cinic acid). 



Along with the albuminoids precipitable by alcohol and coagulable 

 by heat, are various enzymes which we shall take up further on (endo- 

 tryptase, maltase, invertase, glycogenase, lipase, etc.), and especially 

 zymase; but this has not been isolated in the pure state. When placed 

 with fermentable sugars (saccharose, maltose, glucose, levulose) these 

 sugars, after a few minutes, are changed to alcohol. Further on, we 

 shall discuss the properties of this enzyme. 



