Studies on Enzyme Action. 



109 



My best thanks are due to Prof. E. W. MacBride for criticism and 

 suggestions. I have also to express indebtedness to Mr. E. Elmhirst, the 

 Superintendent of the Millport Marine Station, for much care in providing 

 me with material. 



Studies on Enzyme Action. XV.* — Urease : a Selective Enzyme. 

 By Henry E. Armstrong, F.R.S., and Edward Horton. 

 (Received January 26— Read February 1,1912.) 



[International Catalogue of Scientific Literature. 

 Q 831 ll C^ rea )' Hydrolysis by urease (Soja bean). 

 I Urease (Soja bean). Action on urea.] 



Q 8311 

 D 1814| 

 Q 1240J 



The production of urea from the metameric amnionic cyanate by Wohler, 

 in 1828, was naturally regarded as an achievement of great importance in 

 view of the part the substance plays in the human economy — very nearly the 

 whole of the nitrogen secreted being voided as urea ; the synthesis of such 

 a compound was a severe blow to the vitalistic conceptions which had been 

 dominant in organic chemistry and justly excited attention, as it broke down 

 the barriers up to that time held to be existent between the organic and 

 inorganic world. 



The attributes of urea are in many ways remarkable and scarcely in 

 correspondence with the simple formula ordinarily assigned to it. It is 

 generally spoken of in the text-books as carbamide but its properties are 

 more nearly those of the isomeric hydroxy-amino-imino-A.ex'\va l txw&: an 

 explanation may be found in the assumption that the two isodynamic 

 substances are present in an aqueous solution in oscillatory equilibrium : — 



But it is probable that these two compounds, in turn, are in equilibrium with 

 the hydrate common to both, C(NH 2 )2(OH) 2 : as chemical changes are all 

 reciprocal effects, the behaviour of urea is therefore subject to considerable 

 variation and depends on the conditions under which it is placed ; on this 



* XIV, ' Annals of Botany,' 1911, vol. 25, pp. 507—519. I— XIII, these ' Proceedings,' 

 Series B. 



