ENZYMES. FERMENTATION 405 



Demonstration of the Presence of Lipase in Pancreatic Juice. 



The lipase in pancreatic juice may be demonstrated by adding a 

 few drops, or I c.c., to neutral olive oil (about 5 c.c.) containing a 

 drop of phenolphthalein. The mixture is coloured red by running ia 

 iN alkali from a burette. On keeping warm at 40 and occasionally 

 shaking, decolorisation takes place. More alkali is run in, drop by 

 drop, until the red colour again appears. It will disappear again. 

 This can be repeated several times. 



Effect of Bile Salts on Pancreatic Lipase. 



Bile salts increase the rate of hydrolysis of fats by lipase and act 

 as a co-enzyme. This can be demonstrated by the following three 

 experiments : 



(1) 5 c.c. neutral oil + 5 c.c. pancreas extract + I c.c. of water. 



(2) 5 c.c. ,, ,,+5 c.c. + i c.c. of i percent. 



bile salt solution. 



(3) 5 c.c. ,, +5 c.c. boiled + I c.c. of I percent 



bile salt solution. 



These three mixtures are kept at 40 for half an hour and titrated 

 with -iN alkali using phenolphthalein as indicator. No. 3 requires 

 least alkali, No. 2 requires most. More hydrolysis therefore occurs 

 in the presence of bile salts. 



VII. Pepsin. 



A solution of pepsin is readily prepared by treating the mucous membrane 

 of the stomach with glycerin for 12-24 hours and straining the solution 

 through muslin. Before use the glycerin extract is diluted with 2 or 3 

 volumes of water. 



Dry preparations of pepsin in the form of powder or scales are obtained 

 by precipitating aqueous extracts with alcohol, or evaporating them to dryness 

 at a temperature below 40. They generally dissolve slowly in water or -iN 

 hydrochloric acid. A i per cent, solution is convenient for the demonstra- 

 tion of pepsin. f 



As substrate for detecting the presence of pepsin, threads of fibrin 

 or pieces of coagulated white of egg, are generally used. 



The action of pepsin is demonstrated with five test tubes contain- 

 ing the following mixtures : 



(1) 5 c.c. of water + i c.c. of pepsin solution + a piece of fibrin. 



(2) 5 c.c. of -iN HC1 + I c.c. of water + a piece of fibrin. 



(3) 5 c.c. of -iN HC1 + I c.c. of pepsin solution + a piece of fibrin. 



(4) 5 c.c. of -iN HC1 + i c.c. of boiled pepsin solution + a piece 



of fibrin. 



(5) 5 c.c. of -iN Na 2 CO 3 + I c.c. of pepsin solution + a piece of 



fibrin. 



