OF THE 



UNIVERSITY 



OF 



PHYSIOLOGICAL CHEMISTRY. 



CHAPTER I. 



ENZYMES AND THEIR ACTION. 



ACCORDING to the old classification ferments were divided into 

 two classes, the organised ferments and the unorganised ferments. 

 As organized ferments or true ferments there were grouped such 

 substances as yeast and certain bacteria which were supposed to 

 act by virtue of vital processes, whereas the unorganized ferments 

 included salivary amylase (ptyalin), gastric protease (pepsin), 

 pancreatic protease (trypsin), etc., which were described as "non- 

 living unorganized substances of a chemical nature." Kiihne des- 

 ignated this latter class of substances as enzymes (eV fv/*^ in 

 yeast). This division into organized ferments (true ferments) and 

 unorganized ferments (enzymes) was generally accepted and was 

 practically unquestioned until Buchner overthrew it in the year 

 1897 by his epoch-making investigations on zymase. Previous to 

 this time many writers had expressed the opinion that the action of 

 the ferment organisms was similar to that of the unorganized 

 ferments or enzymes and that therefore the activity of the former 

 was possibly due to the production of a substance in the cell, which 

 was in nature similar to an enzyme. Investigation after investiga- 

 tion, however, failed to isolate any such principle from an active 

 cell and the exponents of the " vital " theory became strengthened 

 in their belief that certain fermentative processes brought about 

 by living cells could not occur apart from the biological activity 

 of such cells. However, as early as 1858, Traube had enunciated, 

 in substance, the principles which were destined to be fundamental 

 in our modern theory of fermentation. He expressed the belief 

 that the yeast cell produced a product in its metabolic activities 

 which had the property of reacting with sugar with the production 

 of carbon dioxide and alcohol, and further that. this reaction be- 

 tween the product of the metabolism of the yeast cell and the sugar 



