FERMENTATION OEGANISMS 101 



Exercise 142. The Invertase of Yeast 



Invertase is one of the important enzymes produced by yeast. 

 Its specific action is the hydrolytic splitting of disaccharides to 

 monosaccharides, such as dextrose and levulose (invert sugar), 

 by an action represented by the equation 



Invertase passes out of the yeast cell by exosmosis into the 

 surrounding medium. 



A. A simple and convenient method of demonstrating this is 

 the following: 



1. Prepare a 2 per cent solution of pure cane sugar. Make 

 certain that it has no reducing action on Fehling's solution. 

 Put the solution into several large test tubes or small flasks. 



2. Add to each tube yeast from a yeast cake or from a pure 

 culture. Keep the tubes in a warm place (25° C.) for twenty-four 

 hours. 



3. Test the contents of the inoculated tubes for invert sugar 

 by the use of Fehling's solution. Write the equation for the 

 chemical change in the sugar. 



£. By the use of another method the invertase may be obtained 

 free from living yeast cells. 



1. Wash 10 g. of brewer's or compressed yeast thoroughly 

 with water and filter with suction. 



2. Mix the moist yeast with 100 cc. of distilled water and 

 5 cc. of chloroform. The chloroform prevents the yeast from 

 growing but does not destroy the enzymic action. Keep the 

 solution for three hours at a temperature of 25°-30° C. ; then 

 filter. 



3. To test the inverting action of this solution, add 5 cc. to 

 25 cc. of a 3 per cent cane-sugar solution and keep at 30° C. for 

 an hour or more. Boil the solution to drive off the chloroform, 

 which would otherwise interfere with the test with Fehling's 

 solution. Add distilled water to restore the boiled solution to 

 its original volume and determine the amount of invert sugar 

 quantitatively by Fehling's solution or by the polariscope. 



