LUIS F. LELOIR 



and D-xylose to D-xylulose. These investigations have started 

 recently, so that it is impossible to assess their metabolic im- 

 portance, but it is believed that the enzymes acting on phos- 

 phorylated sugars are of more widespread occurrence. 



Inversion of Configuration 



The transformation of mannose into glucose requires inver- 

 sion at position 2, while a similar change in position 4 leads to 

 the formation of glucose from galactose. Both types of reactions 

 occur in nature. Inversion at 2 has been studied with muscle 

 extracts. Starting with mannose-6-phosphate, the product ob- 

 tained was a mixture of fructose-6-phosphate and glucose-6- 

 phosphate. Since the enzyme acting on mannose phosphate 

 could not be separated from the isomerase which interconverts 

 glucose phosphate into fructose phosphate, it has not been pos- 

 sible to decide whether the primary product is the glucose or the 

 fructose ester. 



Inversion at 4 has been studied with extracts of yeast grown 

 in galactose-containing media. These extracts catalyze the 

 interconversion of a-glucose-1 -phosphate (II) into a-galatose-l- 

 phosphate (III); that is, the inversion of the hydroxyl group at 



Q- 



o- 



CH20H 



.N. 



HC 



HC 



CO 



N 



U 



Sc 



OH 



590 



