1322 



If nc is large, compared with a, the initial velocity is small; a 



larger a gives a greater velocity. On rhe other hand, if nc is small, 



(I 



then even for low urea concentrations is not small and will 



a -\- nc 



sooner approximate to a constant value. 



The values of m were calculated in the tables, either, when y had 

 an appreciable value, from the integrated equation, or from the 

 differential equation for the initial velocity as soon as the urea 

 concentration was high enough to make these equations give the 

 same value. 



The inconstancy of hi will now be shown to afford favourable 

 evidence to the radiation theoiy. 



For in surveying the columns which give the c.c. NHj^^^N, formed 

 in equal times of action, a remarkable featuie will be observed. 



For low pn these values increase continually from 0.03 up to 

 8 7o "I'ea concentration. 



For higher />// there is first an increase and then, in the most 

 concentrated urea solutions, a decrease. 



This is exactly, what the theory would lead us to expect. 



A urease particle being the cejitre of a sphere of action and the 

 action in thi.'^ case producing an alkaline substance, the H-ion con- 

 centration aiound the enzyme particle will be lowered and kept 

 low by the enzyme action itself. This process will be negligible in 

 dilute ui-ea solutions, l)ut in concentrated ones, where the sphere of 

 action is concentrated into a small volume, a marked diminution of 

 the H-ion concentratioji may be expected. 



Bearing in mind the dependence of urease activity m on pu (see 

 Fig. 3), it will be evident, that in solutions of low />// a decrease 

 of the H-ion concentration around the enzyme particles, i.e. a 

 diminution of c, means a rise of ///. Hence for two reasons con- 

 siderably more action is t'ound here in high urea concentrations. 



(( 

 ¥()\-, besides the increase of , there is also an increase in m, 



a -\- ur 



because the />//, though constant as fai- as can be estimated in the 

 solutions as a whole, is increased in the small sphere around the 

 enzyme, to which the action is confined. 



If /)// is not very low, tire production of an alkaline substance 

 ai'ound the enzyme particle may raise ps above the optimum in 

 these phosphate solutions. Hence in the concentrated urea solutions 

 of a pH neai' or above this optimum the pfj may soon be raised 

 so far, that m is diminished. 



{To he continned.) 



