ENZYMES. FERMENTATION. 



In the previous sections an outline has been given of the organic 

 compounds which are found in nature, both in plants and in animals. 

 Their variety is very great, and they include not only simple compounds 

 such as alcohol, glycerol, fatty acids, lactic acid, urea, amino acids, and 

 many others, but also the more complex, such as chlorophyll, haemo- 

 globin, and the three large groups, carbohydrates, fats and proteins. 

 These three groups make up the main portion of the solid matter of 

 plants and animals, and are concerned intimately with the functional 

 activity of the organism. 



We have to investigate how the change from the complex com- 

 pound to the simple, such as starch and glucose to alcohol and carbon 

 dioxide, protein to amino acids, and vice versa from the simple to the 

 complex, is effected in nature. 



The hydrolysis and decomposition of the complex compounds is 

 effected by the reagents grouped together under the term enzymes. 

 The formation of the complex compound from the simple ones is 

 effected by the same reagents. The decomposition is most easily 

 ascertained and followed, but the formation is only followed with 

 difficulty and it has been actually observed only in a few instances. 

 Nevertheless it is believed that the synthesis of all the complex com- 

 pounds is effected by enzymes. 



Historical. 



The formation of alcohol and carbon dioxide from sugar was known to 

 the ancients, and on account of the effervescence, or apparent ebullition of the 

 liquid, during the decomposition of the sugar, the process was called fermenta- 

 tion, tiomjervere, to boil. In the middle ages the decomposition of proteins 

 was recognised as an analogous process to that of fermentation and the terms 

 putrefaction and fermentation were frequently used to denote any process of 

 decomposition. Not until the beginning of the nineteenth century, mainly be- 

 tween 1830 and 1840, was it recognised that fermentation was due to the 

 presence of living cells (Schwann, La Tour, Kiitzing, Pasteur). At about 

 the same time it was discovered that extracts of plants barley and almonds, 

 and a little later that extracts of animal organs of the stomach and pancreas, 

 were able to effect the decomposition of the complex compounds, starch, 

 amygdalin and proteins into simpler ones. The effective substance in barley 

 extract was called diastase, that in almonds, emulsin, that in the stomach, 

 pepsin, that in the pancreas, trypsin. There were thus two varieties of active 

 agents the one living (yeast) the other not living (diastase, etc.), and they 

 were called respectively organised ferments and soluble or unorganised fer- 

 ments. 



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