Studies on Enzyme Action. 



329 



200 c.c. Erlenmeyer Jena flask containing a measured volume (an excess) of 

 standardised chlorhydric acid. In all the experiments, the carbon dioxide 

 present was removed by bubbling air through the mixture to which the 

 standard acid had been added, after a few drops of olive oil had been intro- 

 duced in order to prevent the frothing which otherwise occurs. At the end of 

 an hour the excess of standard acid present was determined by titration with 

 standard baryta solution, using litmus as indicator. 



When dealing with substanoes of slight solubility (e.g. benzaldehyde, 

 methylic salicylate, etc.), 105 c.c. of a solution were prepared having a con- 

 centration of M/4 as regards urea and M/20 as regards the substance to be 

 added ; 100 c.c. of the liquid taken out with a pipette were introduced into 

 the 200 c.c. Jena flask and treated with 25 c.c. of Soja extract as before. 



In most of the experiments made with the object of studying the action of 

 carbon dioxide on more .concentrated solutions of urea (semi-molecular, 

 molecular, twice molecular and pentamolecular), in which samples were taken 

 over a considerable period, the quantity of urea solution used was 200 c.c. 

 together with 50 c.c. of Soja extract. 



Influence of Acid Compounds on the Activity of Urease. 



Not only strong acids but even the relatively much weaker carboxy- 

 acids prevent the enzyme from acting, if present in appreciable amount. 

 Thus no action took place in solutions of Aspartic and Salicylic acids of 

 M/50 strength. 



Boric Acid. — This acid has a remarkable depressant action when present 

 in a solution containing the proportion B2O3/5O as shown in Table A (see 

 Graph No. 12).* 



Phenol. — In M/25 strength phenol itself has little influence but it 

 appears to be sufficiently "acid" in M/5 strength to exercise a marked 

 retarding effect (Table A, Graphs 1 and 2). 



The influence of guaiacol and resorcinol is distinct from that of most other 

 substances. At first these compounds retard the rate of hydrolysis but 

 subsequently accelerate it slightly. Apparently, at the outset, they enter 

 into competition with the enzyme and share the urea with it ; as ammonia 

 is liberated, however, they also serve to neutralise this base and therefore 

 promote the change (Graphs 4, 5 and 6). 



In the presence of quinol, action soon comes to an end (Table B). Only 

 about 2 per cent, of change was effected when the solution was of M/25 



* Apparently boric acid is singular in that it retards the action of urease even in very 

 weak solutions ; all other acids, if present in sufficiently small amount, accelerate 

 hydrolysis. 



