5O METHODS FOR THE STUDY OF FERMENTS 



the expressed juice is mixed with a measured solution 

 of an optically active polypeptide of known compo- 

 sition. The mixture is poured into a polariscope tube 

 and the rotation for the solution is ascertained as 

 quickly as possible. If one then determines the 

 rotation from time to time, an insight into the nature 

 of the decomposition is acquired. Instead of optically 

 active polypeptides we can employ racemic bodies. 

 The latter are optically inactive, because they consist 

 of two halves equally strong as regards their respec- 

 tive rotations in opposite directions. The peptolytic 

 ferments generally decompose only such polypeptides 

 as are built up out of the optically active amino- 

 acids as thev are found in nature. If we have to 



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deal with a racemic polypeptide, of which one-half 

 complies with this condition, then this part is 

 reduced to its component parts, and we are left with 

 the other half of the racemic body, which consists 

 of amino-acids not found in nature. We recognize 

 this asymmetric splitting through the fact that the 

 original optically inactive mixture becomes optically 

 active. 



An example may convey a clear idea of these 

 conditions. In nature we meet the amino-acids 

 l-leucin and d-alanin, while d-lcucin and l-alanin 

 have never yet been found amongst the products of 

 reduction of the proteins. If we allow peptolytic 

 ferments to act on the racemic bodies d-alanvl 



