ENZYMES. 61 



proteins). As above mentioned, the enzymotic decompositions are 

 often complicated by their taking place over several intermediary steps to 

 the final product. As indicated by several conditions, the enzymes also, 

 before they act upon the substrate, combine therewith in some way or 

 another. The fact that the action of an enzyme is dependent upon the 

 stereometric construction (page 67) of the substrate speaks essentially 

 for this view. The substrate also protects certain enzymes against destruc- 

 tive influences (heat, alkalies) 1 ; casein is able to protect trypsin against 

 the retarding influence of seralbumin (HEDIN 2 ) . Trypsin adsorbed by 

 carbon is in part abstracted by proteins (HEDIN 3 ) . According to this 

 only that part of the added enzyme which is combined with the substrate 

 is active. We must now consider the following: 



1. The velocity with which the enzyme combines with the substrate. 



2. The result of the division, i.e., how much of the added enzyme 

 is combined with the substrate. 



3. The velocity of the chemical processes produced by the enzyme. 



The velocity of the combination of the enzyme with the substrate (1) can at 

 least in many cases be ignored in consideration of the time necessary for the 

 chemical reaction. This applies to those cases where the chemical transforma- 

 tion in the presence of an excess of substrate at the beginning of the processes 

 remains the same in each successive time interval. The quantity of enzyme 

 combined with the substrate, does not, in these cases, increase with the time, 

 which would be the case if the time necessary for the combination is not in com- 

 parison with that for the chemical reaction. 



Equal decomposition for equal time at the beginning of the processes have 

 been found for the following enzymes invertase, 4 diastase, 5 trypsin with casein. 6 



The second question, as to the division of the enzyme between different bodies, 

 we will discuss after we have spoken of the velocity of the real chemical reaction 

 as well as the retardation of enzyme action. 



In regard to question 3, it must be recalled that the following laws 

 have been found for catalytic reactions: 



1. When the quantity of catalyst remains constant, the reaction 

 velocity for every moment is proportional to the concentration of the 

 body decomposed, which is shown by the velocity coefficient in the same 

 experiment being constant at different times. 



1 O'Sullivan and Thompson, Journ. Chem. Soc., 57, 926, 1890; Bayliss and Starling, 

 Journ. of Physiol., 30, 71, 1903; Hedin, ibid., 30, 173, 1903; 32, 474, 1905; Taylor, 

 Journ. of biol. Chem., 2, 90, 1906. 



2 Journ. of Physiol., 32, 390, 1905, also Zeitschr. f. physiol. Chem., 50, 497, 1907. 



3 Bioch. Journ., 2, 81, 1906. 



4 O'Sullivan and Thompson, Journ. Chem. Soc., 57, 926, 1890; Ducleau, TraitS 

 de microbiologie 11, 137; Brown, Trans. Chem. Soc., 81, 373, 1902; Armstrong, Proc. 

 Hoy. Soc., 73, 500, 1904. 



5 Brown and Gliddinning, Proc. Chem. Soc., 18, 43, 1902. 



6 Hedin, Journ. of Physiol, 32, 471, 1905. 



