164 AGEICULT.UEAL AND INDUSTRIAL BACTERIOLOGY 



bacteria known which will ferment inulin but whether the 

 inulin is attacked directly or first broken down into levulose 

 has not been proved. 



Three of the common disaceharides are frequently used in 

 the study of microorganisms. These are sucrose or cane 

 sugar, maltose or malt sugar, and lactose or milk sugar. 

 These are hydrolyzed by the enzymes sucrose, maltase and 

 lactase respectively. The reaction may be indicated as 

 follows : 



C12H22O,, + HjO + invertase = C.H.^O, + C^U^^O^ + invertase 



Many species of molds and yeasts are known which produce 

 one or more of these enzymes. Common bread yeast, for 

 example, produces the enzymes sucrase and maltase but not 

 lactase. Certain of the lactic yeasts, however, are able to 

 produce lactase as well. These enzymes are collectively 

 known as invertases, and the process of hydrolysis of a 

 disaccharide is termed an inversion. It should here be 

 remarked as under starch fermentation, that many bacteria 

 are capable of attacking disaceharides without hydrolyzing 

 them into the simple sugars ; that is, the fact that a micro- 

 organism can ferment sucrose does not indicate that it 

 necessarily produces the enzyme sucrase, or that dextrose 

 and levulose are intermediate products in the fermentation. 

 Proteases and Amidases. — In the discussion of the nitro- 

 gen cycle it was noted that proteins are exceedingly complex 

 nitrogenous organic compounds built up by the polymeriza- 

 tion of alpha amino acids. The hydrolysis of these com- 

 pounds is brought about by a group of enzymes termed pro- 

 teases and amidases. Those most common are the pepsins, 

 the trypsins, and the erepsins. The pepsins are enzymes 



