44 ORIGIN AND MAINTEN. OF OPT. ACTIVITY 



by the plant, is stored not as such but combined with 

 gentiobiose in the form of 3-giucoside (natural amyg'da- 

 line). The latter easily crystallizes from water solutions, 

 while the glucoside which consists of gentiobiose and of 

 the left nitrite of mandelic acid possesses such a high 

 solubility that it does not, in general, crystallize from 

 water solutions (Walker and Krieble, 1909; Krieble, 

 1912).^ So, the fact that pure natural amygdaline is de- 

 posited in the plant does not necessarily postulate the 

 existence of an optically specific enzyme, synthesizing only 

 the right nitrite of mandelic acid. The right and the left 

 nitrites may be produced; then the right component pre- 

 cipitates in the form of gentiobioside ; the excess left 

 nitrile can thereupon be racemized according to the re- 

 quirements of true catalysis ; the right nitrile originating 

 from this process is again bound to gentiobiose and the 

 process continues until all the nitrile is converted into the 

 less soluble gentiobioside of the right nitrile, i.e., into pure 

 natural amygdaline. The same final state would evi- 

 dently ensue no matter whether the enzyme possesses the 

 capacity of preferential synthesis of the right nitrile or if 

 it would synthesize racemic nitrile. In the latter case, 

 however, the gradual catalytic transformation of the left 

 component into the initial substance (benzaldehyde and 

 hydrocyanic acid) and the resynthesis of the right com- 

 ponent would demand a long time, which is evidently 

 spared by the utilization of an optically specific enzyme. 

 Natural optically active gentiobiose is a stereo-autonomic 

 substance in the sense that it conditions the stable optical 

 purity of the synthetic product. Kuhn sees a confirmation 

 of his views in the fact that, in the fruits of Prunns 

 laurocerasus, one finds a gentiobioside of the pure right 

 nitrile of mandelic acid, while, in the leaves of the same 

 plant, one finds a glucoside of the racemic nitrile. It is 

 probable that the difference in solubility brought about 



1 Similar differences are found, in general, in diastereomers, that is, in 

 substances consisting of one antipode of a substance A combined Avitli either 

 of the tAvo antipodes of a substance B. For example, AiBi and AiBa are 

 two diastereomers. 



