SPECIFIC NATURE OF CATALYTIC ACTION 135 



stratum must fit like key and lock, or the reaction does not 

 occur. 



A similar selective action is seen in the case of the organisms 

 which induce fermentation, as was known before the date of 

 Fischer's researches upon the enzymes, as a result of the investi- 

 gations of Pasteur, who showed that only dextro-rotatory racemic 

 acid was attacked, and was able to separate the Isevo-rotatory 

 stereo-isomer by such means. It is only those sugars with six 

 or nine carbon atoms that are fermentable, and of these only certain 

 of the stereo-isomers belonging to the " d " series. This fact 

 has been used by Fischer for the purpose of separating the "Z" 

 stereo-isomers from the inactive mixture of " d " and " I " sugars 

 obtained by synthetic procedures. 



That the hydrolytic action of enzymes upon the sugars depends 

 upon the stereo-isomeric form has been clearly demonstrated by 

 E. Fischer, E. Fischer and E. Frankland Armstrong, and other 

 observers, by the action upon derivatives of the fermentable or 

 hydrolysable sugars. By combination of the hexoses with methylic 

 alcohol, the methyl-hexoses are obtained. In each such case two 

 stereo-isomeric compounds are obtained, which Fischer termed 

 a and /3 compounds. Thus from glucose and methyl- alcohol one 

 obtains a-methyl-glucoside, and /3-methyl-glucoside. If now the 

 effect of the yeast enzymes is tested upon these two artificial 

 compounds, which only differ in their stereo-chemical relationships, 

 it is found that only the a -modification is hydrolysed, the /3 one 

 being quite resistant. If instead of the yeast enzymes, however, 

 the emulsin enzymes be employed, the ft compound is now the 

 one which is attacked, similarly to a large number of naturally 

 occurring glucosides. 



In collaboration with E. F. Armstrong, Fischer extended his 

 observations to show that the same laws held in the case of other 

 sugar derivatives, such as the osones and artificial disaccharides. 



It can accordingly be predicted, when the constitution and 

 stereo-chemical relations of a body are known from its derivation, 

 whether it will be attacked by a given enzyme or not. 



It is worthy of note that it is not whether a sugar is artificial 

 or natural which determines the attack, but whether it possesses 

 a certain molecular configuration the identity of which must extend 

 even into stereo-chemical exactness. Hence it follows that the 

 specific action does not mean that an enzyme can attack one sub- 



