CARBOHYDRATE ENZYMES 63 



But some decompose it simply into levulose and melibiose, causing 

 only the levulose to ferment; others are able to take it further. They 

 act on the melibiose which they change to dextrose and galactose; 

 this is fermented to d-glucose. The dissociation of raffinose is, then, 

 the work of two enzymes, raffinase and melitriase, which split the raf- 

 finose into levulose and melibiose, and a melibiase which splits the 

 melibiose into dextrose and galactose. 



Ci 2 H 22 On + H 2 O = C 6 H 12 O 6 + C 6 Hi 2 O 6 

 Melibiose Dextrose Galactose 



Saccharomycodes Ludwigii, S. marxianus, exiguus, thermantitonum, 

 cartilaginosus, Sch. Pombe, mellacei, octosporus, the yeasts E and F of 

 Rose, and the yeast of Logos cause raffinose and levulose to ferment 

 but not melibiose. They contain only a raffinase. On the contrary, 

 bottom yeast of the Frohberg and Saaz types cause melibiose and 

 levulose to ferment while the top yeasts of these types are able to 

 ferment .only levulose and do not possess a melibiase. 



According to Kalanthar, a melizitase exists in some yeasts which 

 decomposes melizitose into dextrose and turanose. 



+ H 2 = 

 Melizitose Glucose Turanose 



Disaccharides : Sucrase, Maltase, Lactase, Trehalase: The di- 

 saccharides possess the general formula Ci 2 H 22 On. Four of them, 

 saccharose, maltose, lactose and trehalose, are well known. 



Saccharose is changed by sucrase or invertase to glucose and levu- 

 lose. The phenomenon may be expressed by the following equation: 



Ci 2 H 22 On + H^O = CeH^Oe -f- CeH^Oe 

 Saccharose Glucose Levulose 



It was in the yeasts that Berthelot found sucrase for the first time. 

 It is rather widely distributed among them. In certain species, this 

 enzyme remains inside of the cell and only that sucrose which passes 

 into the cell, is decomposed. The glucose and levulose thus formed 

 diffuse through the membrane into the medium. But in Monilia 

 Candida and in the yeast of "Soja" not only the sucrase remains in 

 the cell but also the glucose and levulose, whether it is not able to 

 diffuse or whether it is destroyed as soon as it is formed. Thus it 

 is impossible to observe the inversion of sucrose by an analysis of the 

 fermentation mixture. But in many yeasts, sucrase is diffusible, and 

 is able to be secreted outside of the cell. Finally certain yeasts, as 

 Sch. octosporus, S. apiculatus, Behrensianus, Rouxii, mali Duclauxi, 

 P. membranafaciens, W. belgica, do not possess sucrase and are, conse- 

 quently, unable to ferment sucrose. 



