120 Prof. H. E. Armstrong and Mr. E. Horton. [Jan. 26, 



Again, when at the end of an experiment (when the action was complete and 

 therefore the products of change were present in a proportion equivalent to 

 the urea originally present) a fresh quantity of urea, equal to that originally 

 taken, was added, the rate at which hydrolysis took place initially was about 

 one-third of that first observed and the time required to effect complete 

 hydrolysis was more than doubled. 



In another experiment, in which a third portion of urea was introduced, 

 hydrolysis took place at a very slow rate, 12 per cent, being changed after 

 30 minutes in this third stage instead of 10 per cent, in the second stage and 

 25 instead of 97 per cent, at the end of six hours. 



Inasmuch as ammonia had so much more influence in retarding change than 

 the carbonate, it appeared probable that the effect was attributable to its 

 acting as an alkali. But it was conceivable that by favouring the activity of 

 proteoclastic enzymes associated with the urease it might promote the 

 destruction of the enzyme rather than retard its action. 



Stability of the Enzyme. — To test the stability of the enzyme under various 

 conditions, 25 c.c. of an extract prepared in the manner previously described 

 was diluted to 250 c.c. with water; a second 25 c.c. was diluted to 250 c.c, 

 sufficient ammonia being added to make the solution N/500 NH 3 in concen- 

 tration ; a third 25 c.c. was similarly diluted with water and acidulated 

 to be of the strength N/500 HC1; a portion of the extract was set aside 

 undiluted. The activity of each of these solutions towards urea was tested as 

 soon as they were made and after various intervals and in the case of the 

 acid and alkaline liquids, two experiments were made with each solution — 



Table V. 



Enzyme solution. 



Percentage of urea hydrolysed in mixtures of 20 c.c. 

 enzyme solution and 20 c.c. 2M/5 urea solution 

 in 1 hour at 25°. 



Initial. 



• 



day. 



3 



4 



7 



11 



17 



60 



Aqueous solution of 10 per cent. 



25 -3 



25 -3 



24 -3 





23 -8 



23 -3 



21 -5 



9-6 



of Soja extract [kept] 



















Ditto [made at time of experi- 



25 -3 



25 -7 



24 -9 





23 -7 



23 -1 



21 -5 



10 -4 



ment] 



N/500 NH 3 solution of 10 per 



25 -9 



25 -2 



24 -1 





23 -3 



22 -7 







cent, of Soja extract [kept] 



















Ditto [neutralised at time of 



25 -9 



25 -3 



24 -6 





22 -7 



23 -7 



22 -8 



11 -0 



experiment] 



















N/500 HC1 solution of 10 per 



25 -9 



25 -0 



21 -4 



19 -6 



17 -3 



15 -5 







cent, of Soja extract [kept] 



















Ditto [neutralised at time of 



25 -5 



24 -1 



21 -0 



18 -9 



17 -1 



14 -5 



11 -9 



3 1 



experiment] 



















