184 



A SYMPOSIUM ON RESPIRATORY ENZYMES 



only glucose from the equilibrium mixture of fructose- and glucose- 

 6-phosphate. 



When fructose is added to liver or kidney extract, it is also con- 

 verted to glucose. This involves phosphorylation of fructose and 

 splitting of the glucose-6-phosphate in equilibrium with fructose-6- 

 phosphate. Table 6 illustrates an experiment in which an aerobic 

 phosphorylation of fructose took place with partial conversion to 

 glucose. In this experiment glutamate was used as oxidizable sub- 

 strate, which caused a considerable consumption of oxygen. The 

 respiration, as in other cases of aerobic phosphorylation, serves here 

 for the regeneration of adenosinetriphosphate, the phosphate donor 



Table 6.— Aerobic conversion of fructose to glucose in dialyzed rat 



hver dispersion 



(All samples contained 0.2 mg. Mg++, a catalytic amount of adenosinetriphosphate, 

 and 0.025 M phosphate buffer of pH 7.3, in a volume of 1.4 cc. Incubated 60 minutes 

 at 37°C.) 



to fructose. When no fluoride is added only a small amount of 

 phosphate ester accumulates, and most of the fructose that disap- 

 pears is converted to glucose. Fructose and glucose were determined 

 by separate methods. In the presence of fluoride, dephosphorylation 

 is inhibited and consequently more hexosephosphate esters accumu- 

 late and less glucose is formed. When no phosphate acceptor is 

 added, a small amount of inorganic phosphate is esterified, espe- 

 cially when fluoride is added. This compound is almost exclusively 

 pyrophosphate, as has been mentioned previously. 



The mechanism of the conversion of fructose to glucose is shown 

 in Table 7, the enzyme system consisting of adenosinetriphos- 

 phate, kidney phosphatase prepared by Albers' method, and yeast 

 hexokinase— which also contains Lohmann's enzyme (11). If hexo- 

 kinase is not added, neither adenosinetriphosphate nor fructose 

 disappears. When phosphatase is omitted, all the added adenosine- 



