208 III. OXIDATION AND METABOLISM 



Gidez and Karnovsky'^^'' reported that, when C'*-tagged glycerol was 

 given to intact rats, only insignificant differences in metabolism were 

 noted, irrespective of whether the alcohol was given intraperitoneally, in- 

 tragastrically, or intravenously. A constant proportion was oxidized to 

 CO2 when doses ranging from 30 to 238 mg. were administered. It was 

 calculated that 70 to 100% of the newly-synthesized blood glucose originated 

 from the administered glycerol, while only 15 to 39% of the newly-formed 

 glycogen could be traced to this source. 



Moreover, Doerschuk^^^ demonstrated that the organism converts 

 glycerol into the glycerol moiety of the triglycerides as well as into the 

 glycerophosphoric acid portion of the phospholipids, lecithin, and cephalin. 

 However, Gidez and Karnovsky'^^'' observed that the hver triglyceride glyc- 

 erol reached a specific activity about three times that of phosphatide 

 glycerol, although the activity declined more rapidly in the triglyceride 

 than in the phospholipid fraction. It was also noted that tagged glycerol 

 was present in the lipids of most tissues examined, including the brain 

 lipids. 



The mechanism of synthesis of glucose from glycerol with isotopically- 

 marked glycerol has been found to be more complex than was originally 

 supposed. Thus, Doerschuk^^' reported that, when glycerol- 1,3-C'^ was 

 administered to rats, radioactivity occurred mainly on carbons 1, 3, 4, and 

 6 of the glucose; it was beheved that this indicated a preliminary oxidation 

 and phosphorylation to dihydroxyacetone phosphate or D-3-phosphoglyc- 

 eraldehyde, which was followed by known reactions of glycolysis.'^- 

 Schambye and Wood,^^' using glycerol-1-C^^, came to similar conclusions. 

 These latter workers reported that the tracer pattern of the carbon chain of 

 glucose was unsymmetrical, since C3 contained 1.4 to 2.4 times as much 

 C^* as did C4. This hypothesis proves that the end-carbons of glycerol are 

 not metabolically identical, and is in harmony with the Ogston hypothesis,^®* 

 that "the asymmetrical occurrence of isotope in a product cannot be taken 

 as conclusive evidence against its arising from a syinmetrical precursor." 

 Swick and Nakao,'^®^ on the basis of examination of the glucose formed in the 

 rat after feeding glycerol-1-C^*, demonstrated variations in the radioactivity 

 of the carbons in positions 3 and 4 which contained about 91% of the 

 radioactivity. These workers likewise state that glycerol, like citric acid, 



7«> L. I. Gidez and M. L. Karnovsky, /. Biol. Chem., 206, 229-242 (1954). 



7" A. P. Doerschuk, /. Biol. Chem., 196, 423-426 (1952). 



^«2 C. F. Cori and W. M. Shine, Science, 82, 134-135 (1935). 



^«3 P. Schambye and H. G. Wood, /. Biol. Chem., 206, 875-882 (1954). 



^" A. G. Ogston, Nature, 162, 963 (1948). 



'»R. W. Swick and A. Nakao, J. Biol Chem., 206, 883-886 (1954). 



