1129 



100 cc), c is the concentration of the H-ions (also in grams per 

 100 C.C) and n is the coetïicient of absorption of the H-ions, i.e., 

 one gram of H-ions absorbs n times as much radiation as one gram 

 of urea. 



The velocity-constant m for a given temperature and H-ion con- 

 centration is proportional to the concentration of enzyme only, if 

 both temperature and H-ion concentration are maintained really 

 constant. 



Calling the initial urea concentration a, expressed like x and c in 

 grams per 100 c.c, putting 



a — X 

 a 

 substituting this in (1), we get 



, «(1— V) ,, .„. 



ady = m at (J) 



«(1— y) + "« 



After integration and introduction of decimallogarithms the general 

 equation for the reaction-velocity of urease at constant temperature 

 and constant H-ion concentration becomes 



nc 1 



log \- ay ^= mt (3) 



0,434 l — y 



3. Determination of the constant n. 



For the estimation of the important constant n it was necessary, 

 not only to determine accuiately the H-ion concentration c, but also 

 to take care, that c and thereby also m (as will be seen further 

 on) remained unchanged from beginning to end of the reaction. 

 Now, the hydrolysis of urea to ammonium-carbonate is in so far a 

 dilTicult case for enzyme study, that here by the enzyme-action 

 itself a distinctly alkaline substance is formed out of a neutral 

 substrate. This production of alkali is so considerable, that even in 

 presence of a buffer mixture of 8 % phosphate only 0.01 7o or at 

 the utmost 0.02 "/o of urea can be allowed to be transformed, if 

 one wants to maintain anything like constancy of />//. 



A study of the kinetics of urease-action without the addition of 

 a powerful buffer to keep the true reaction constant, is evidently 

 as useless as working without a thermostat in a room of widely 

 changing temperature. 



In fixing the best conditions for the experimental determination 

 of ■this constant ?7, two considerations determined the choice of the 

 Ph of the regulating phosphate mixture. 



