ENZYMES. 59 



In all these cases the enzymes are obtained strongly contaminated 

 with other bodies. No enzyme has thus far been obtained in a per- 

 fectly pure form, and the chemical constitution as well as structure 

 is therefore unknown. The enzymes probably belong to the colloids; 

 if they themselves are not colloids, they occur at least with col- 

 loids, from which they cannot be separated. The enzymes are character- 

 ized by the fact that they are readily taken up by finely divided sub- 

 stances (inorganic precipitates, carbon, kaolin, infusorial earth and other 

 colloids such as alumina, iron hydroxide, proteins 1 ). This process may 

 act selectively, as from a solution certain enzymes can be taken up and 

 others not at all, or only to a slight extent (HEDiN, 2 MICH.AELIS and EHREN- 



REICH 3 ). 



All enzymes lose their specific action on sufficiently heating their 

 aqueous solutions, and even at ordinary temperature the enzymes are 

 gradually decomposed. MADSEN and WALBUM have followed this 

 process at different temperatures and found that the decomposition 

 of trypsin, pepsin and rennin at given temperatures proceeds mono- 

 molecularly, i.e., that the velocity of reaction at every moment is pro- 

 portional to the concentration of the enzyme (page 54) . 4 The readiness 

 with which an enzyme is decomposed is nevertheless to a great extent 

 dependent upon the presence of other bodies (page 61). 



Certain enzymes are also sensitive to light. According to SCHMIDT- 

 NiELSEN 5 chymosin is injured by light and indeed, by the ultra-violet 

 rays. The experiments of JODLBAUER and TAPPEINER 6 with invertin 

 have led to the same results; the visible rays also can in certain cases 

 (peroxidase, hsemase) in the presence of oxygen or certain fluorescent 

 substances exert an injurious action. 7 



Just as it is difficult to prepare an enzyme free from non-enzymotic 

 contaminations, so also is it difficult to exclude the possibility that a 

 so-called enzyme is not a mixture of several related enzymes. In fact 

 the several enzymotic processes proceed step by step, and it is possible 

 that the various steps are caused by different enzymes. This seems 

 according to BUCHNER and collaborators 8 to be the case in alcoholic 

 fermentation, in which the dextrose is probably first split into lactic 



1 Dauwe, Hofmeister's Beitrage, 6, 426, 1905. 



2 Bioch. Journ., 2, 112, 1907. 



3 Bioch. Zeitschr., 10, 283, 1908. 



4 Arrhenius, Immunochemie, Leipzig, 1907, 5? 



5 Hofmeister's Beitrage, 5, 355, 1904; 8, 481 1906; Zeitschr. f. physiol. Chem., 58, 

 233, 1908. 



6 Arch. f. klin. Med., 87, 373, 1906. 



7 Bioch. Zeitschr., 8, 61 and 84, 1908. 



8 Ber. d. d. chem. Gesellsch., 37, 419, 1904; 38, 620, 1905. 



