48 SCIENCE PROGRESS 



P. edule contains a cyanogenetic glucoside. The seeds of 

 Taraktogenos Kitrsii, 1 which are now recognised as the source 

 of chaulmugra oil, have been shown by Power and Gornall to 

 contain a cyanogenetic compound, from which prussic acid is 

 readily obtained by the action of acids or the specific enzyme 

 also present in the seeds ; according to Jouck the related plant 

 T. Blumei has also been found to yield prussic acid. 



Glucosidolytic Enzymes 



It is unfortunate that so far no satisfactory method of 

 characterising enzymes has been discovered, and consequently 

 it has become almost customary to assume that where a gluco- 

 side occurs in a plant in association with an enzyme which 

 decomposes it, the latter is specific in its action. 



This tendency has been rather less marked since Fischer 

 discovered that glucosides were capable of existing in two 

 isomeric forms derived respectively from a-glucose and /3-glucose, 

 and that there appears to be a certain relationship between the 

 configuration of the glucoside and that of the enzyme which 

 is capable of decomposing it. Thus Fischer 2 found that yeast 

 ferment (maltase) was only capable of hydrolysing a-glucosides 

 and emulsin of decomposing /3-glucosides. 



The enzymes associated with cyanogenesis in plants have, 

 however, not as yet been systematically studied, except in the 

 case of the emulsin of almonds, which is now known to be a 

 ^-enzyme — i.e. it is capable of decomposing /3-glucosides. The 

 action of emulsin on amygdalin presents some features of interest. 

 Since this glucoside is decomposed both by yeast enzyme (mal- 

 tase) and by emulsin, it must be at once an a- and a /3-glucoside — 

 i.e. of the two glucose residues present in the molecule, one must 

 exist in the a and the other in the /3 form. It is curious, how- 

 ever, that while maltase attacks amygdalin in such a way as to 

 liberate only one molecule of glucose (presumably a-glucose), 

 leaving the rest of the molecule (mandelic nitrile glucoside) 

 intact, emulsin attacks amygdalin in such a way as to lead to 

 complete decomposition, producing presumably a molecule each 

 of a- and /3-glucose. This complete decomposition of amygdalin 

 by emulsin can be accounted for if it may be assumed that 

 the enzyme first splits the glucoside into benzaldehydecyan- 



1 Power and Gornall, loc. cit. 2 Fischer, loc. cit. 



