VARIOUS DISACCHARIDES 73 



mentable by yeast ; this statement is, however, probably not 

 strictly true, since pure cultures of yeast containing only 

 zymase, the active enzyme which produces alcoholic fermenta- 

 tion, have no action on maltose. Ordinary brewers' yeast, 

 however, contains maltase, which first hydrolyses maltose to 

 grape sugar, which is then fermented by zymase. Only sugars 

 containing six carbon atoms are fermentable by yeast (see 

 P- 377> 



ISO-MALTOSE. 



Iso-maltose is a disaccharide which is isomeric with and 

 closely related to ordinary maltose, its optical activity, 

 D = + 139-140, being almost the same as that of mal- 

 tose; it is formed, together with ordinary maltose, when 

 diastase acts on starch, provided the enzyme is not present in 

 too large a quantity ; the most favourable temperature for its 

 production is 65-70. Iso-maltose is also formed together 

 with dextrin by the action of concentrated hydrochloric acid 

 on glucose at a temperature of 10-15, which accounts for the 

 fact that it is not infrequently met with as an impurity in 

 commercial glucose prepared by the action of hydrochloric 

 acid on starch (see p. 61). 



CELLOBIOSE. 



Cellobiose is the name given to a disaccharide obtained 

 by the hydrolysis of cellulose (see p. 135). 



MYCOSE OR TREHALOSE. 



Mycose or trehalose is the name given to a disaccharide 

 found in various agarics, notably Boletus edulis, and also in 

 moulds such as Aspergillus niger. It does not reduce Fehling's 

 solution and is strongly dextro-rotatory, d = + 1 99. When 

 boiled in acids it is slowly converted into glucose.* 



AGAVOSE AND LUPEOSE. 



Agavose j- and lupeose J similarly are disaccharides which 

 have been isolated from the stem of Agave americana and 

 lupin seeds respectively. 



* Winterstein : " Z. physiol. Chem.," 1894, 19, 70. 



t Midland and Tristan : " Amer. Chem J.," 1892, 14, 548. 



iSchulze: " Ber. deut. chem. Ges.," 1892, 25, 2213. 



