472 



LECTURE XX. 



following formula of a non-fermentable sugar, d-talose, will show what 

 a slight difference in the configuration in the molecule may prevent the 

 action of the yeast : 



COH 



HO . C . H 

 HO . C . H 

 HO . C . H 

 H . C . OH 



CH 2 . OH 



d-Talose 



Although, from what was said about zymase, we can conceive of the 

 selective behavior of the cells of Penicillium glaucum, yeasts, etc., as due 

 to the action of ferments, it is nevertheless desirable to perform such 

 experiments with the individual ferments themselves. In many cases the 

 cell, with its ferments, may conceal such a specific action on account of 

 the acting together of ferments of different kinds. Emil Fischer has suc- 

 ceeded in showing that the specific activity of the cells is dependent upon 

 the ferments contained therein. If aldoses are heated with very weak, 

 alcoholic hydrochloric acid, we obtain two isomeric glucosides, which are 

 designated as the a- and /^-compounds. Emil Fischer has assigned the 

 following formulas to these methyl derivatives of d-glucose : 



OH 



OH 



Only one of these two compounds, in fact the /?-form, is hydrolyzed by 

 emulsin into methyl alcohol and grape-sugar; the a-form remains unacted 

 upon by this ferment. On the other hand, ferments obtained from yeast 

 do not attack the /?-glucoside, but hydrolyze the a-form. The stereo- 

 isomers of the above compounds, a-methyl-Z-glucoside and /?-methyl- 

 Z-glucoside, are not attacked by either emulsin or the yeast ferments. 



