1912.] 



Studies on Enzyme Action, 



115 



20 c.c. of Soja extract diluted with 20 c.c. of water were closed with india- 

 rubber stoppers through which passed glass tubes provided with indiarubber 

 tubes and screw clips. The flasks were exhausted slightly and then kept in 

 incubators at 25°. After 24 hours, the contents of each flask was heated 

 to boiling and distilled in a current of steam during 15 minutes, excessive 

 frothing of the solutions containing enzyme being prevented by addition of 

 a few drops of olive oil. Each distillate was collected in 10 c.c. of a 

 standardised solution of chlorhyclric acid ; the distillate was then heated to 

 boiling to expel carbon dioxide, cooled and titrated with baryta solution, 

 using litmus as indicator. The results are given in Table I. 



Table I. — Action of Soja Urease on Substituted Ureas. 





Standard acid neutralised by 



Amount of hydrolysis of 



Substituted 



distillate from 





Urea + enzyme. 





Urea alone. 



Urea + enzyme. 



Urea alone. 



Uncorr. 



Corrected for 

 enzyme. 



Methylurea 



s-Dirnethylurea . . . 

 a.s-Dimethylurea ... 



o-o 



0-5 

 2 

 0-6 



c.c. 

 0-45 

 0-8 



0- 2 



1- 65 



per cent. 



0-3 

 0-1 

 0-4 



per cent. 

 0-3 

 0-5 



0- i 



1- 



per cent. 

 0-15 

 0-4 



o-o 



0'9 



.s-Diethvlurea 



0-25 



0-35 



0-25 

 0-3 



0-15 

 0-15 



0-15 

 0-12 



0-03 

 0-05 







The evidence thus obtained appears to us to be conclusive proof that 

 urease is capable of acting only on urea itself — in other words, it exercises a 

 purely selective effect and must, like other enzymes, in some way correspond 

 very closely in structure with the hydrolyte urea with which alone it is in 

 correlation. 



The value of such correlation will be realised more fully perhaps when it 

 is stated that either acid or alkali of normal strength may be kept in 

 contact with urea during several days at 25° without any perceptible degree 

 of hydrolysis being effected, though in the presence of the enzyme the urea is 

 resolved rapidly into ammonia and carbonic acid. 



Time Bate of Change of Urea by Soja Urease — Effect of Concentration. — In 

 our earliest experiments we were struck by the fact that the graphs repre- 

 senting the course of the change were of extreme flatness in comparison 

 with those representative, of the action of other enzymes. On attempting to 

 effect the hydrolysis at a> constant rate by means of a very small proportion 

 of enzyme, using M/o solutions of urea, we found that though, in the later 



I 2 



