GENERAL CHEMISTRY OF LIFE PHENOMENA 2$ 



stereoisomeres, of which, however, only three are fermentable by 

 Saccharomyces cerevisice, namely, <^glucose, rf-mannose, and (^galactose. 

 The relation between fermentability and configuration will be rendered 

 a little clearer by the following diagrams: — 



H H OH H 



1. CH.OH C C C C COH ^-glucose (fermentable) 



OH OH H OH 



OH OH H OH 



2. CH.OH C C C C COH /-glucose (nonfermentable) 



H H OH H 



H H OH OH 



3. CH2OH C C C C COH ^-mannose (fermentable) 



OH OH H H 



HO HO H H 



4. CH2OH C C C C COH /-mannose (nonfermentable) 



H H OH OH 



H OH OH H 



5. CH.OH C C C C COH ^-galactose (fermentable) 



OH H H OH 



etc. 



Fischer gave a metaphorical illustration of these facts which was 

 taken rather literally by some biologists, and which has had a decided 

 influence upon the formation of biological hypotheses. For this reason 

 it may be mentioned here. " Inasmuch as the enzymes are in all proba- 

 bility proteins, and inasmuch as the latter are formed synthetically from 

 carbohydrates, it is probable that their molecules also have a dissym- 

 metrical structure, and one whose dissymmetry is, on the whole, com- 

 parable to that of hexoses. Only if enzyme and fermentable substance 

 have a similar geometrical shape can the two molecules approach each 

 other close enough for the production of a chemical reaction. Meta- 

 phorically we may say that enzyme and glucoside must fit into each other 

 like key and lock." 



Max Cremer* has expressed the idea that in all these cases in reality 

 one and the same sugar undergoes alcoholic fermentation; namely, 

 <f-glucose. It is, indeed, not imppssible that the alcohohc fermentation 

 of c?-mannose and rf-galactose occurs in two stages, the first stage con- 

 sisting in the transformation of these two substances into dextrose. This 

 would be in harmony with the observations concerning the alcoholic 

 fermentation of disaccharides, e.g. cane sugar, which must first be 

 * Max Cremer, Zeitsch.Jur Biologic, Vol. 32, p. 49, 1895. 



