64 PHYSIOLOGY OF YEASTS 



Maltose in order to be assimilated and fermented must also be 

 decomposed by an enzyme into two molecules of glucose. This is 

 accomplished by maltase. 



C 12 H 22 U + H 2 = C 6 H 12 6 + C 6 H 12 6 



Maltose Glucose Glucose 



Many yeasts at once decompose maltose and saccharose (S. cere- 

 visiae Pastorianus, intermedius, validus, ellipsoideus, and turbidans). 

 On the contrary, S. marxianus, exiguus, Jorgensenii, Saccharomy- 

 codes Ludwigii and Saccharomyces guttulatus, are able to ferment sac- 

 charose but do not ferment maltose. Maltase is then a different 

 enzyme from sucrase. Other yeasts such as S. apiculatus ferment 

 neither maltose nor saccharose, and thus possess neither maltase nor 

 sucrase. Maltase is a reversible enzyme and transforms maltose 

 into isomaltose. 



For lactose to undergo alcoholic fermentation, it must first be 

 changed by lactase into glucose and galactose. 



Ci 2 H 22 On + H 2 = CeHiijOe + 



Yeasts possessing a lactase are not common. Only a small number 

 are known. Lactase has been found in S. Kephir (Beijerinck), tyrocola 

 fragilis, acidi lactici, lactis a and ft (Dombrowski), Zyg. lactis, the 

 yeasts of Duclaux, Adametz, and Kayser, and various Torula and 

 Mycoderma isolated by Dombrowski, etc. Hunter l has mentioned a 

 yeast which was able to ferment the lactose in cream. This yeast 

 apparently possessed a lactase. Hunter also reviews the literature 

 on yeasts which possess this enzyme. Several such instances are men- 

 tioned. 



Trehalose is decomposed by trehalase into glucose and levulose. 

 Many yeasts seem to possess a trehalase and are thus able to hydrolyze 

 trehalose. 



Kalanthar has found it in many beer and wine yeasts. S. ther- 

 mantitonum and the bottom yeast of Frohberg (Linder) also contain 

 trehalase. 



Neuberg and Karczag 2 found that pyroracemic and oxymalic acids 

 were fermented with the formation of carbon dioxide. Acet alde- 

 hyde was identified as the other product. This would indicate that 

 a carboxylase removed the CO 2 from the pyroracemic acid. Carbon 

 dioxide was also split from the following acids: acetone dicarboxylic, 

 chelidonic, dihydroxytartaric, phenylglyoxylic and acetylenedicar- 



1 Hunter, O. W. A Lactose Fermenting Yeast Producing Foamy Cream. 

 Journal of Bacteriology, 3 (1918) 293-300. 



2 Neuberg, C. and Karczag, L. Carboxylase, a new enzyme of yeast. Bio- 

 chem. Zeit. 36, 68-75. 76-81; Chem. Abstracts, 6 (1912), 380. 



