M. Wheldalb 139 



or again one may have a retarding influence and the other none, as for 

 instance in the case of invertase, which is retarded by fructose, whereas 

 glucose has no effect. 



There is little doubt that the retarding influence is due to the fact 

 that the enzyme enters into some form of compound with the sugar 

 and is thereby removed from the sphere of activity, with the resultant 

 slowing down of the hydrolytic process. 



There is a similar retardation in many cases in the synthetic process 

 due to the combination of enzyme with the substrate. A full account 

 of these retardation processes is given by Bayliss in The Nature of 

 Enzyme Action. 



The enzymes with which we are chiefly concerned in the present 

 paper comprise the glucoside-splitting class. The term glucoside is 

 applied to a large number of substances occurring in plants, all of 

 which have the property of being hydrolysed by enzymes or by acids 

 into glucose and one or more other products such as alcohols, aldehydes, 

 phenols, etc' 



In some cases a glucoside, as, for example, xanthorhamnin, is only 

 hydrolysed, as far as we know, by one particular enzyme, rhamnase, 

 though sometimes one enzyme, such as emulsin, will hydrolyse a con- 

 siderable number of different glucosides, i.e. arbutin, salicin, coniferin, 

 syringin, helicin, amygdalin, aesculin, daphnin, and others. 



An interesting point in connection with the glucoside-splitting class 

 of enzymes is the rapidity with which the hydrolytic reactions take 

 place when the plant is submitted to the action of chloroform vapour 

 or other anaesthetics. Injury to the tissues will also bring about the 

 same result. This reaction is readily detected if the products of 

 hydrolysis have a characteristic odour, as for instance in the case of 

 cyanogenetic glucosides, of which amygdalin is the best known example. 

 Amygdalin occurs in bitter almonds and in the kernels of peaches, 

 apricots, plums and other fruits of the Rosaceae. By emulsin it is 

 hydrolysed according to the equation : — 



a„H2;0uN + 2H.,0 = CVHeO + HON + 2C,B.,,0, 



amygdalin benzal- hydrogen glucose 



dehyde cyanide 



and the progress of the reaction can be detected by means of the 

 characteristic odour of the products. 



1 An account of these substances is given by E. F. Armstrong in The Simple Carbo- 

 hydrates and Glucosides. 



10—2 



