The biosynthesis of pentoses and their incorporation into mononucleotides 



During our study of the phosphoribomutase we found (Klenow, 1953) that the ratio 

 between the activity of this enzyme in muscle extract and that of the phosphogluco- 

 mutase was altered only slightly during preparation of the latter as a crystalline 

 enzyme (Najjar, 1948). Furthermore, it was found that the ribomutase reaction under 

 certain conditions could be activated by glucose- 1,6-diphosphate (see Figure 4). This 

 suggested that the phosphoglucomutase could catalyse the transfer of a phosphate of 

 glucose- 1,6-diphosphate to ribose- 1 -phosphate, whereby a ribose-i,-5-diphosphate 

 might be formed. This presumed that ribose- 1,5-diphosphate might then function as 

 a coenzyme for the phosphoribomutase reaction. Further evidence for the reaction 



-0.02 



W mm 



Figure 5. Formation of glucose-6-phosphate from ribose- 1 -phosphate 

 and glucose-i ^-diphosphate. 



Glucose- 1,6-diphosphate: 6 X io -5 m; ribose- 1 -phosphate: 3 x io -4 m; 

 triphosphopyridine nucleotide: i -2 X io -4 m; magnesium chloride: 2 X io -3 

 m; glycyl-glycine cysteine buffer pH 7-2:1 X io -2 m; crystalline phosphogluco- 

 mutase: 0-015 mg. protein per ml.; £wischenferment : 0-5 mg. protein per ml. 

 ©complete O control without ribose- 1 -phosphate; X control without glucose- 

 1 ,6-diphosphate. The reaction is measured in a spectrophotometer at 340 rmt. 



between ribose- 1 -phosphate and glucose- 1,6-diphosphate was obtained with glucose- 

 6-phosphate dehydrogenase {^wischenferment) and triphosphopyridine nucleotide. 

 With this system it could be demonstrated that glucose-6-phosphate is formed from 

 glucose- 1,6-diphosphate in the presence of ribose- 1 -phosphate and phosphogluco- 

 mutase (Klenow and Emberland, 1954) (see Figure 5). In the same system it could 

 furthermore be shown that not only ribose- 1 -phosphate, but also deoxyribose-i- 

 phosphate and galactose- 1 -phosphate can serve as acceptors of a phosphate from 

 glucose- 1,6-diphosphate (Klenow, 1953). From incubation mixtures of ribose- 1- 



75 



