32 



OPTICAL ACTIVATION 



isomers which, lon account of their configuration, belong to one 

 group. ThuSj for example, he has founcU that d- glucose, 

 d- mannose, d- galactose, and d- fructose all undergo 

 fermentation with yeast, while the laevo isomers of these sub- 

 stances do not. Xot onlv, however, are the micro-organisms 

 able to distinguish between isomers of entirely opposed activity, 

 but the transposition of two groups, attached to a single one of 

 a number of asjanmetric carbon atoms, is of importance to them. 

 Fischer and Thierfelder^ have shown that although the above 

 mentioned sugars are fermentable by various yeasts, d- talose, 

 which differs from d- mannose and d- galactose only by the 

 transposition of the groups attached to a single asymmetric 

 carbon atom, is not attacked by the same yeast species. To 

 insure enzyme action, then, the substrate and enzyme must have 

 their configurations adjusted to one another like lock and key; 

 and it may be possible that they may act on one another to their 

 mutual distruction if the keys turn opposite ways. However, 

 experiments made by Eiloart showed no such destruction in the 

 case of human and pig pepsins. 



The relation between the substrate molecule and that of the 

 enzyme is illustrated^ by the splitting lof a - — • and ^ — methyl 



H— C— OCH, 



H— C— OH 

 I 

 HO— C— H 



I / 

 H— C 



I 

 H— C— OH 



I 



CH,— OH 



H3CO— C— H 



1. Fischer, E.: Zeit. f. physiol. Cheni.. 26, 60, (1898). 



Fischer, E., and Thierfelder: Bar. d. deutsch .chem. Ges., 27, 2031. 



(1894); see also Fischer, ibid. 27, 29S5, 3228, 3479. 

 3. Fischer, E.: ibid. 32, 3617, (1899). 



