PHYSIOLOGICAL CHEMISTRY 



CHAPTER I 

 ENZYMES AND THEIR ACTION 



According to the old classification ferments were divided into two 

 classes, the organized ferments and the unorganized ferments. As organ- 

 ized 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 designated this latter class of substances as 

 enzymes (kv ^u/zrj 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 Wv 

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

 nature similar to an enzyme. Investigation after investigation, how- 

 ever, 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 has enunciated, in substance, the principles 

 which were destined to be fundamental in our modern theory of fermen- 

 tation. 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 between the product of the metabolism of the yeast cell and the 

 sugar occurred without aid from the original cell. It was not until 1897, 

 however, that this theory was placed upon a firm experimental basis. 

 This was brought about through the efforts of Buchner, who succeeded in 

 isolating from the living yeast cells a substance (zymase) which, when 

 freed from the last trace of organized cellular material, was able to bring 



