Chemistry. — " Urease and the radlation-tJieory of enzyme-action". 



By Dv. H. P. BARENDRECHT. 



(Communicated in the meeting of February 22, 1919). 



I. 



1 . Since the discovery by Takeuchi of urease in tiie Soja-beans an 

 exceptionally useful material for the study of enzyme-action has 

 been at our disposal. The enzyme as well as the pure substrate, 

 urea, are now readily obtainable in unlimited quantity. The estima- 

 tion of the reaction products can be carried out easily and accurately, 

 an important condition for success in pioneerswork, where innume- 

 rable analyses have to be niade. 



This chance of solving to some extent the great riddle of enzyme- 

 action has therefore attracted many woikers during the last few years. 



Marshall (J. Biol. Chem. XVII, p. 351, 1914) has found, that 

 in this case also the action is proportional to the concentration of 

 the enzyme. 



The Armstrong's, Horton and Benjamin (Proc. Roy. Soc. 1912 

 and 1913) have made extensive empirical studies, from which the^^ 

 drew the conclusion, that ammonia retards, but carbonic acid 

 accelerates the reaction, a surprising result, which others also state 

 to have found. As will be seen from the present paper, pure 

 chemical empiricism here leads to false conclusions. 



A ru'st endeavour to theoretical as well as to experimental study 

 of the action of urease was made by Donald van Slykk and his 

 collaborators (J. Biol. Chem. XIX, p. 141, 1914). 



To clear the field it is necessary to pass some criticism on this work. 



The theoiy of these authors and all their further work are based 

 principally on three experiments. In experiments 1 and 2 "the effect 

 of concentration of urea, enzyme concentration being constant" and 

 "the effect of decreasing urea concentration on reaction, as the latter 

 approaches completion" were investigated. As in these experiments 

 the considerable changes in concentration of the hydrogen-ions were 

 left out of consideration, notwithstanding the authors themselves have 

 further on become aware, that the urease activity is dependent in 

 a high degree on the H-ion concentration, it is no wonder, that they 



