REVERSIBILITY 473 



stroyed diastase, and since then several other authors have 

 described similar effects for other enzymes.* 



The action of radium and radium emanation on enzymes 

 has been studied by Wilcock,t by Loewenthal and Edelstein,$ 

 by Bickel, by Loewenthal and Wohlgemut, and others. § 



REVERSIBILITY OF ENZYME ACTION. 



Comment has above been made on the decrease in the 

 velocity constant of enzyme action after a certain point has 

 been reached ; the enzyme appears to become less active. 

 This may be accounted for in one of two ways : either by the 

 assumption that the products of the reaction combine with 

 the enzyme or, by their concentration, exercise some inhibiting 

 influence upon the enzyme ; or else by assuming that the 

 tendency for the reverse action to take place has a retarding 

 effect. 



That there should be a tendency for the reverse reaction 

 to take place is a perfectly legitimate conclusion ; in fact 

 van't Hoff long ago pointed out that a catalyst which accele- 

 rates a reaction in one direction must also be able to exert an 

 accelerating effect on the reverse reaction. Consequently the 

 same enzymes which effect hydrolyses should also, under 

 suitable conditions, be able to synthesize. 



The first experimental proof of this was given by Croft 

 Hill, 11 who showed that when maltase was allowed to act on 

 a concentrated solution of glucose, the disaccharide maltose 

 was produced ; later it was shown ^ that the disaccharide iso- 

 lactose could be synthesized from galactose and glucose by the 

 action of lactase from Kefir. Since then a large number of 

 enzymatic syntheses have been effected. 



* E.g. Burge, Fischer, and Neill : " Amer. Journ. Physiol.," 1916, 40, 

 137, 426. 



t Wilcock : " Journ. Physiol.," 1907, 34. 



J Loewenthal and Edelstein : " Biochem. Zeit.," 1908, 14, 484. 



§ Loewenthal and Wohlgemut: id.. 1909, 21, 476. Laborde and 

 Lemay : " Compt. rend. Soc. bioL," 1921, 85, 497. 



II Croft Hill : " J. Chem. Soc. Lond.," 1898, 73, 634. 



^ Fischer and Armstrong : "Ber. deut. chem. Gesells.," 1902, 35, 3144. 



