GLYCEROL 45 



Another procedure for demonstrating the convertibility of glycerol to 

 glucose is by proving that it reduces ketonuria. Only substances which are 

 convertible to glucose are believed to have a ketolytic effect. ^"^ Thus, 

 Hirschfeld,'"'' Satta,-"^ and Lang^'^^ reported that the ingestion of glycerol by 

 diabetic or by normal fasting human subjects is followed by a decrease in 

 ketonuria. Moreover, Shapiro, ^"^ employing the procedure of exogenous 

 ketonuria with the fasting rat, demonstrated that glycerol reduced the 

 excretion of ketone bodies to the same extent as did an isodynamic amount 

 of glucose. 



Not only has the experimental evidence left little doubt that a quanti- 

 tative conversion of glycerol to glucose or to glycogen can take place in 

 normal animals, but the proof of the opposite reaction is ecjually convincing. 

 Freeman and Friedemann-^" demonstrated that, after the feeding of oleic 

 acid to dogs, the acid was recovered exclusively as triglyceride in the lymph; 

 this result was interpreted as a direct proof of the synthesis of glycerol in the 

 gut wall. 



The appearance of glycerol arising from glucose in the process of gly- 

 colysis in tissues and in the fermentation with yeast offers another ex- 

 ample of the glucose -»■ glycerol transformation. Thus, West and Todd^^^ 

 suggest that, in the breakdown of glycogen and glucose in the liver, the 

 Harden- Young ester (fructose-l,6-diphosphate) gives rise to dihydroxy- 

 acetone phosphate; the latter compound can be converted to a-glycerol 

 phosphate (and hence to glycerol) or to 3-phosphoglyceric aldehyde. The 

 latter substance is not ordinarily the main source of glycerol, although it 

 can be converted to this polyhydric alcohol. The sequence of reactions 

 which result in glycerol production is shown on the following page. 



In the fermentation of glucose with yeast, small amounts of glycerol are 

 produced, in addition to ethyl alcohol. ^^^ In this instance, the immediate 

 source of the glycerol is believed to be 3-phosphoglyceric aldehyde, which 

 is converted to a-glycerol phosphate by diphosphopyridine nucleotide 

 (DPN) under the influence of a-glycerophosphate dehydrogenase. When 

 a-glycerophosphate is acted on by phosphatase, free glycerol is formed. 



Experiments with lactating animals have provided additional evidence 

 that glucose can serve as the mother substance of glycerol. Under such 

 conditions, the synthesis of glycerol apparently takes place in the mam- 



20^ F. Hirschfeld, Z. klin. Med., 28, 176-209 (1895); 31, 212-278 (1897). 

 »8 G. Satta, Beitr. Chem. Physiol. Pathol, 6, 376-391 (1905). 

 «>9R. M. Lang, Biochem. J., 9, 456-478 (1915). 



=»>» S. Freeman and J. E. Friedemann, /. Biol. Chem., 108, 471-478 (1935). 

 *" E. S. West and W. R. Todd, Textbook of Biochemistry, Macmillan, New York, 1955, 

 p. 965. 



