1907.] Cyanogenesis in Plants. 317 



The statement that phaseolunatin is decomposed by the emulsin of 

 almonds must therefore be withdrawn. It is probable that in the cases 

 (recorded by Jorissen,* Jouck,f and in the third paper of this seriesj) in 

 which the liberation of prussic acid from phaseohmatin has been attributed 

 to the action of emulsin the decomposition was in reality due to some 

 secondary cause and not to the direct agency of emulsin. 



There is, therefore, the fundamental difference between the emulsin of 

 almonds and the enzymes occurring in Phaseolus lunatics beans, flax, and 

 cassava, that whilst emulsin decomposes amygclalin and salicin and is 

 without action on phaseolunatin, the enzymes of Phaseolus lunatus, flax, and 

 cassava decompose all three of these glucosides. The question at once arises 

 as to whether the enzyme associated with phaseolunatin in these three plants 

 is merely an enzyme of the emulsin type having a greater range of activity, 

 or is a mixture of emulsin with a second enzyme, and that the decomposition 

 of phaseolunatin is due to the action of the latter. The first of these 

 hypotheses seems at first sight the more plausible, since it is difficult to admit 

 that the same mixture of two enzymes should occur in the three plants 

 already mentioned, especially since none of them contains, so far as has been 

 ascertained, any glucoside or complex sugar which could be attacked by 

 emulsin. The further evidence we have obtained, however, leaves no doubt 

 that, accepting present theories of enzyme action, these three plants do 

 contain two enzymes, one of the emulsin type and the other of the maltase 

 type.§ It is probable that to the action of the " maltase " the decomposition 

 of phaseolunatin is due. 



Fischer 1 1 has shown that the glucosidolytic enzymes so far systematically 

 examined are divisible into two classes, the one capable of decomposing the 

 a-alkyl ethers of the hexoses and the other the stereo-isomeric /3-alkyl ethers 

 of these sugars. The first class of enzymes may be regarded as typified by 

 the maltase of yeast and the second by the emulsin of almonds. 



It is obviously possible from Fischer's generalisation to classify an 



* Jorissen, loc. cit. 



f Jouck, loc. cit. 



X Dunstan and Henry, loc. cit. 



§ Since the present investigation was concluded, some results have been published by 

 Marino and Fiorentino ( f Gaz. Chim. Ital., 5 1906, vol. 36, p. 395), which seem to indicate 

 that the maltase of malt is capable of decomposing both a- and /3-glucosides ; thus, 

 according to these authors, it effects the decomposition both of maltose and salicin. They 

 reject the obvious and simple explanation of these anomalous results, viz., that the maltase 

 they used contained emulsin, on what appear to be insufficient grounds. If their conclu- 

 sions were established, our present views respecting the nature and mode of action of the 

 group of glucosidolytic enzymes would require to be considerably modified. 



|| 'Zeit. Physiol. Chem.,' 1898, vol. 26, p. 75. 



2 A 2 



