INTERCONVERSION OF SUGARS 



With this new enzyme together with aldolase and transketo- 

 lase, the number of possible interconversions between ketoses 

 becomes enormous. 



Redox Reactions 



The initial studies of Warburg on the oxidation of glucose- 

 6-phosphate at position 1 have been followed by several workers, 

 and it has been found that the following sequence of reactions is 

 catalyzed by enzymes present in plant and animals: 



TPN 



glucose-6-phosphate y ^ 6-phosphogluconoIactone ^ ' 



— CO2 

 6-phosphogluconic acid ^ ^ ribuIose-5-phosphate ^ 



TPN 



ribose-5-phosphate (11) 



A point of interest is that all the reactions have been proved 

 to be reversible (9), so that starting with ribulose-5-phosphate, 

 COo, and an appropriate reductant, it is possible to convert 

 ribulose phosphate into glucose phosphate. This set of enzymes, 

 therefore, provides a method for lengthening or shortening the 

 carbon atom chain by one unit. 



A similar oxidation of free glucose to gluconic acid has been 

 found to be catalyzed by mold and liver enzymes. 



The product of oxidation at position 6 of glucose is glu- 

 curonic acid, which is frequently found in nature. It is well 

 known to mammalian physiologists as a "detoxifying substance," 



597 



