1190 ENZYMES OR SOLUBLE FERMENTS. 



Special Description of the More Important Enzymes. 



Ptyalin. 



While occurring chiefly and characteristically in saliva, a 

 similar enzyme may be obtained in minute amount, but fairly 

 constantly from almost any tissue or fluid of the body, more 

 particularly in the case of the pig. Most recently this enzyme 

 has been prepared as follows. Saliva is diluted with an equal 

 volume of water and saturated with neutral ammonium sulphate. 

 The precipitate thus formed is treated on the filter for five min- 

 utes with strong alcohol, removed from the filter and further 

 treated with absolute alcohol for one or two days. It is now 

 dried at 30° and yields, on extraction with a volume of water 

 equal to that of the original saliva, a solution which is actively 

 zymolytic and is stated to be free from all proteid reactions. 

 The hydrolytic activity of ptyalin is most marked in neutral 

 or nearly neutral solutions. 



An amylolytic enzyme is found in urine. 



Evidence of the existence of a zymogen of ptyalin (ptyalin- 

 ogen) has been obtained in the case of the saliva of the horse. 



The amylolytic enzymes of the pancreas and intestine. 



The secretion of the pancreas is even more active than saliva 

 in effecting the hydrolysis of starch. This property is depen- 

 dent upon the presence in this secretion of an enzyme which 

 in many ways closely resembles ptyalin, but differs from it 

 markedly in its greater power of effecting a more complete 

 decomposition of the starch than can ptyalin. Under ordinary 

 conditions the only sugar formed by the action of ptyalin on 

 starch is maltose. The pancreatic enzyme on the other hand 

 not only rapidly converts starch into maltose, but further con- 

 verts this maltose into dextrose in considerable quantity during 

 a digestion of relatively short duration. The secretion of the 

 pancreas is of extremely complicated composition and contains 

 in addition to the amylolytic at least two other well-character- 

 ized enzymes ; from these the former has as yet been only very 

 imperfectly separated, so that scarcely anything is known of 

 its chemical nature as distinct from its converting powers. An 

 active amylolytic extract is best prepared by extracting finely 

 minced pancreas for five or six days with four times its weight 

 of 25 p.c. alcohol, the mixture being frequently stirred. The 

 pancreas of the pig yields the most certainly active extracts and 

 more particularly if the gland is kept for 21 hours after removal 

 from the body, and is then treated for a few hours with dilute 

 (•5 p.c.) acetic acid before its final extraction with alcohol. 

 Extracts made with strong solutions of sodium chloride are also 

 frequently very active. 



