62 PHYSICAL CHEMISTRY IN BIOLOGY. 



2. The velocity coefficient or the reaction velocity with constant 

 concentration of substrate is proportional to the quantity of catalyst. 



The first law has been shown for certain enzymes in case an excess 

 of enzyme is present, namely for invertin, 1 lactase 2 and trypsin. 3 It 

 was found that the decomposition in a certain time was proportional to 

 the substrate. In other cases the determination of the correctness of 

 the law was accomplished with difficulty. A part of the enzyme may 

 during an experiment be either destroyed or in other ways (combining 

 with the product) be put out of action; then reverse reactions may take 

 place (page 65) and finally in many cases our analytical methods are 

 incapable of obtaining comparative results for different decompositions, 

 as the reaction in many cases takes place step by step, or several 

 reactions occur at the same time. 4 Only in a few cases with especially 

 simple reactions have constant values been found for the velocity 

 coefficient at the beginning, as long as the quantity of reaction product 

 was small and the active quantity of enzyme remained unchanged. 

 With the aid of the formula for a monomolecular reaction 



1 . C 



t C-x 



(page 54), constant values were obtained for the velocity coefficient k in 

 the following cases: 



1. Decomposition of H 2 O2 by catalasc from blood (hsemase 5 ). 



2. Decomposition of H 2 O2 by catalase from Boletus scaber. 6 



3. Decomposition of ethyl butyrate by an enzyme from pig fat. 6 



4. Decomposition of amyl butyrate by an enzyme from the pancreas. 7 



5. Decomposition of triolein and triacetin by an enzyme from the 

 castor oil seed. 8 



6. Decomposition of glycyl-glycine by erepsin. 9 



The reaction is in these cases monomolecular. Although probably 

 most enzymotic cleavage processes proceed with an excess of water 

 monomolecularly, still the proof of this is only exceptionally found. 

 Indeed such an apparently simple reaction as the inversion of cane- 



1 Brown, Proc. chem. Soc., 18, 14, I'.HU. 



2 Armstrong, Froc. Roy. Soc., 73, 500, 1904. 



3 Hedin, Journ. of Physiol., 32, 475, 1905. 



4 Hedin, Zeitschr. f. physiol. Chem., 57, 468, 1908. 



5 Senter, Zeitschr. f. physik. Chem., 44, 257, 1903. 

 " Miller, Hofmeister's Beitrage, 7, 1, IWti. 



7 Dietz, Zeitschr. f. physiol. Chem., 52, 311, 1907. 



8 Taylor, Journ. of biol. Chem., 2, 93, 1906; Nicloux, Compt. rend. soc. biol., ,">(. 

 840, 1904. 



9 Euler, Zeitschr. f. physiol. Chem., 51, 213, 1907. 



