VELOCITY OF REACTION 77 



however, is the proportionality a linear one, the effect being pro- 

 portionately less as the concentration rises. 



If the effect of diminishing the concentration of the substratum 

 as well as that of increasing products of reaction be eliminated, 

 the curve becomes a straight line. 



There is no evidence of actual destruction of trypsin in digesting 

 solutions up to the seventh or eighth hour at 38 C., but trypsin 

 solutions alone rapidly lose activity when kept even at C. 



When kept for some time at a warm temperature, trypsin in 

 solution becomes converted into a body resembling a " toxoid," 

 which may be termed a " zymoid." This body appears to have 

 retained its power of combination with the substratum while becom- 

 ing comparatively inactive as regards its proteoclastic powers. 1 



The chief cause of the increase of the electrical conductivity 

 in trypsin digestion is probably the splitting off of the inorganic 

 constituents of the substratum molecules ; and also, in the case of 

 caseinogen, to the conversion of organic phosphorus into inorganic 

 phosphates. The change of internal friction has, apparently, very 

 little part in the effect. This production of electrolytes is insuffi- 

 cient to account for the retarding action of the products of re- 

 action, they being present in too small a concentration in the total 

 products. 



There is some evidence that amino-acids are more active as 

 retarding agents than the constituents, such as albumoses and 

 peptones, present as chief constituents of the products of the earlier 

 stage of the reaction. 



The retarding action of the products is on the enzyme rather 

 than on the substratum ; and their mode of action is, most probably, 

 by combining with the enzyme and withdrawing it from the sphere 

 of action. This is supported by the fact that they are at least as 

 active as the substratum in protecting trypsin from destruction by 

 heat. 



Trypsin is capable of acting on caseinogen at a temperature as 

 low as C. 



An anti-trypsin is present in egg-white and serum, which slowly 

 disappears during the reaction with trypsin. 



The biuret reaction commences to disappear as early as 2J hours 

 after the commencement of the action of trypsin on caseinogen. 

 The viscosity of caseinogen solutions undergoes a rapid diminution 

 and then becomes constant, while the conductivity curve continues 

 to rise fairly rapidly. 



1 This statement is based on the fact that warmed trypsin solution, when 

 added to gelatine, causes a marked and immediate fall in conductivity. 



