INTERGONVERSION OF SUGARS 



Trehalose phosphate had been previously prepared by 

 Robison and Morgan from the mixture of sugar esters formed 

 during the fermentation of sugars by dried yeast. 



Free trehalose is found in some plants, in yeast, and in fungi. 

 In mushrooms it tends to disappear with age and is replaced by 

 mannitol. Trehalose is considered to be some sort of storage 

 form of sugar in those organisms which do not store sucrose. 



The discovery of the role of UDPG as glucose donor imme- 

 diately leads to speculation on the role of the other uridine- 

 pyrophosphate-containing substances. The formation of phenol 

 glucuronides from phenol and UDP-glucuronic acid has already 

 been mentioned. As to UDP-galactose, it might transfer galac- 

 tose to glucose or glucose phosphate to yield lactose or lactose 

 phosphate. In this connection, it should be pointed out that 

 lactose is /3-galactosyl-4-glucose, whereas in sucrose and tre- 

 halose, and also in UDPG, the linkage of glucose is a. Therefore, 

 the synthesis of sucrose and trehalose takes place without inver- 

 sion, whereas for lactose it would be accompanied by inversion. 

 That such a type of inversion can take place was proved by 

 Fitting and Doudoroff (7) in a study of a bacterial enzyme which 

 catalyzes the following reaction : 



maltose (a:-glucosyl-4-glucose) + phosphate ^ ^ 



/3-glucose-l -phosphate -\- glucose (24) 



Moreover, phenol glucuronides are usually jS, and if UDP- 

 glucuronic acid is a, like UDPG, an inversion should take place 

 in this reaction also. 



Disaccharides and higher saccharides can be formed by 

 enzymes whose main action is hydrolytic (1). To take the case 

 of lactase, the events may be pictured as follows. The substrate, 

 lactose, reacts with lactase to give a galactosyl-enzyme com- 

 pound which then reacts with an — OH-containing substance 

 which may be water or another molecule. The reaction product 

 will depend on the type of acceptor available, and since water is 

 usually the most abundant, the main reaction will be a hydrolysis 

 of the galactosyl-enzyme compound. However, if galactose con- 



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