106 



ENZYMES 



sugars which are dextrorotatory are more readily hydrolysed 

 than their laevorotatory isomers. The mould penicillium glaucum 

 destroys Z-leucine and d-glutamic acid without having any ex- 

 tensive action on d-leucine or Z-glutamic acid. 



Fischer showed that the proteoclastic enzyme, trypsin, acted 

 asymmetrically on synthetic polypeptides, e.g. inactive d.L- 

 alanyl-leucine was digested in such a way that only the compound 

 of d-alanine and Meucine was hydrolysed, whereas the compound 

 of d-alanine and d-leucine was undigested. That is, the natural 



FIG. 18. Diagram of a carbon atom (A) having its valencies- supplied with four 

 different atoms B, C, D, E. The mirror image of this structure would be its optical 

 isomer. 



isomers were destroyed by the enzyme before the isomers not 

 occurring in nature were manifestly attacked. 



Much research has been done to elucidate the reason for this 

 preferential treatment, and some fanciful explanations have 

 been put forward. The problem is a difficult one and the bias 

 of the enzyme at present inexplicable. One fact, however, may 

 be of importance for future development, viz. : if inactive reagents 

 are used to destroy or produce compounds having an asymmetric 

 C atom, then both isomers will be produced or destroyed equally ; 

 if, on the other hand, optically active agents are employed, one 

 isomer has preferential treatment. 



