248 V. OXIDATION AND METABOLISM OF PHOSPHOLIPIDS 



residue of serine, remaining after deamination, is largely converted to glu- 

 cose and to glycogen. On the basis of the phlorhizin technic, Dakin^'' 

 showed that serine, cysteine, proline, ornithine, and arginine yield large 

 amounts of glucose. These results are supported by the qualitative ex- 

 periments of Butts et al.^^ and of Schofield and Lewis,^^ who demonstrated 

 that glycogen stores increased after the feeding of serine to fasted rats. 

 After conversion to glucose, the serine carbons follow the usual fate of the 

 carbohydrate molecule in the animal body. Barnet and Wick^^ fed C'^- 

 labeled glycine to rats, and found that the carboxyl carbon supplied ap- 

 proximately one carbon to each twenty-eight carbon atoms incorporated 

 into glycogen. One carbon atom in every 8.5 carbon atoms in the glycogen 

 molecule was derived from the a-carbon of the fed glycine. This is com- 

 patible with the pathway of conversion of glycine to glycogen suggested by 

 Sakami.'^^ 



{//-) Sphingosine 



Sphingosine, CH3-(CH2)i2-CH:CfI-CHOH-CH(NH2) -CH.OH, is the 

 nitrogenous base present in the sphingomyelin molecule. Although Zabin 

 and Mead^^ reported that sphingosine is synthesized from acetate, little is 

 known concerning the degradation products. It is established that 

 sphingosine is readily reduced to dihydrosphingosine, CHa- (CH2)l4•- 

 CHOH•CH(NH2) -0112011, but it is not known whether this is an inter- 

 mediate in the decomposition of sphingosine or whether it is merely a side- 

 product. Apparently, dihydrosphingosine is a normal product, since it is 

 found in nerve tissue and brain f^ its concentration was shown to be higher 

 in spinal cord than in brain. ^° Lesuk and Anderson**' likewise recorded its 

 presence in the larval form (Cysticercus fasciolaris) of the cat tapeworm 

 {Taenia crassicollis) . However, White et alP stated in 1954 that "Neither 

 the origin nor the fate of . . . sphingosine and dihydrosphingosine is known. 

 Since they are not essential in the diet, these nitrogenous bases presumably 

 can be synthesized in the mammalian organism." 



8* H. D. Dakin, J. Biol. Chem., U, 321-333 (1913). 



86 J. S. Butts, H. Blunden, and M. S. Dunn, J. Biol. Chem., 124, 709-714 (1938). 



86 F. A. Schofield and H. B. Lewis, /. Biol. Chem., 169, 373-378 (1947). 



87 H. N. Barnet and A. N. Wick, /. Biol. Chem., 186, 657-661 (1950). 

 88 1. Zabin and J. F. Mead, /. Biol. Chem., 205, 271-277 (1953). 



89 H. E. Carter and W. P. Norris, /. Biol. Chem., 145, 709 (1942). 



90 H. E. Carter, W. P. Norris, F. J. Click, G. E. Phillips, and R. Harris, /. Biol. 

 Chem., 170, 269-283 (1947). 



" A. Lesuk and R. J. Anderson, J. Biol. Chem., ISO, 457-469 (1941\ 



