JOHN H. NORTHROP 233 



Comparison of the Course of the Reaction as Followed by the Formal 

 Titration of the Solution and by the Change in Conductivity. 



The most significant determination as regards the hydrolysis of 

 proteins is the increase in amino or carboxyl groups. It was found 

 that under the conditions adhered to in these experiments the increase 

 in carboxyl groups is directly proportional to the increase in the con- 

 ductivity. This is shown in Fig. 2. The values obtained by the con- 

 ductivity method therefore represent the actual course of the hydrolysis. 

 This is not true under all conditions. It was found that at other ranges 

 of acidity the two determinations are not parallel. The change in 

 conductivity is also dependent on the alkali used to bring the gelatin 

 to the required pH. It is greatest in ammoniacal solution and may 

 even decrease instead of increase in concentrated phosphate solutions. 



Since the rate of hydrolysis is to be used to determine the amount 

 of trypsin present it is necessary to have some method of expressing 

 the velocity of the hydrolysis. This value should be independent 

 of the stage of the hydrolysis at which the determination is made 

 since otherwise it would evidently be possible to obtain a series of 

 values depending on what stage of the hydrolysis was chosen. The 

 most satisfactory figure for such purposes is of course the constant 

 obtained by substituting the observed values in some equation such 

 as the monomolecular reaction equation. The hydrolysis as carried 

 out in these experiments, however, does not follow accurately any 

 of the simple reaction formulas so that this method cannot be used. 

 It was found that the reciprocal of the time required to cause a defi- 

 nite change was very nearly directly proportional to the concentra- 

 tion of trypsin; i.e., QT = K. Where Q is the concentration of tryp- 

 sin, T the time required to cause a given small change, and A' is a 

 constant. As Arrhenius^ has pointed out, this is a general property 

 of enzymes even though they do not follow the formula for a mono- 

 molecular reaction. This rule has been found to hold for trypsin by 

 Taylor,^ Henri, * Vernon," Hedin,'- and Bayliss,^ whereas Griitzner^' 

 states that the rule does not hold, but that the reciprocal of the time 



" Vernon, U.M., J. Physiol., 1904, x.xx, 330. 

 '2 Hcdin, S. G., J. Physiol., 1905, xxxii, 468. 

 '^ von Griitzncr, P.. Arch. ges. Physiol., 1911, cxli, 63. 



