1912.] 



Studies on Enzyme Action. 



123 



and other chlorides on the hydrolysis of urea by urease. Potassium and 

 sodium chloride act alike, both retarding the rate of change to a moderate 

 extent. Ammonium chloride has a very slight accelerating effect, about 

 equal to that exercised by glucose ; methylurea, on the other hand, has as 

 great an effect in retarding change as have potassium and sodium chloride. 

 The various substances were present in the same molecular proportion as 

 the urea at the outset. The results are represented in the set of graphs 

 on p. 125 and in Table VIII. 



Nature of the Process of Hydrolysis. — In view of the results we have 

 obtained, there is reason to suppose that urease, like all other enzymes 

 hitherto examined, is a selective enzyme — that is to say, an enzyme which 

 fits the hydrolyte of which it is the specific hydrolyst. This hydrolyte may 

 well be the hydrated form of urea, C(OH) 2 (NH 2 )2, rather than urea itself. 



The question to be considered is the nature of the change by which the 

 urea is broken down. It seems to us that there is no reason to suppose 

 that it is resolved otherwise than into carbonic acid and ammonia by a 

 direct process of hydrolysis ; the only intermediate product the formation 

 of which should be considered is carbamic acid. 



It has been argued by Fawsitt (loc. cit.) that the formation of carbonate 

 from urea involves the intermediate conversion of the urea into cyanate 

 but it may be contended that his argument is inconclusive and indeed 

 irrational. In the light of modern knowledge, neither the conversion of 

 urea into amnionic cyanate nor the reverse change can be looked upon 

 as a simple process of internal molecular rearrangement ; in both cases 

 doubtless, a series of changes take place. 



The formation of urea from the cyanate is probably a process involving 

 both hydration and dehydration and may be represented, with some degree of 

 probability, in the manner pictured in the equations on p. 112. 



The formation of carbonic acid and ammonia from urea, on the other hand, 

 is clearly a process of hydration and hydrolysis. It is conceivable and in 

 our opinion probable that both changes — that into cyanate and' that into 

 carbonate — have their origin in the same substance, the hydrated compound 

 which may be supposed to be present in a solution of urea C(OH) 2 (IsrH2)2. 

 Whilst this compound can give rise to cyanic acid, if deprived of ammonia 

 and hydrone (OH 2 ) ; if hydrolysed, it can give rise to orthocarbonic acid 

 and ammonia — 



