204 



E. Hammarsten 



dependent to a large extent on the precursor used. The ideal 

 precursor should be directly incorporated into both of the 

 actual substances without any intermediates. 



In order to investigate to what degree glycine has been 

 incorporated as an intact molecule, thrice marked glycine 

 was used, and the excess of isotopes was determined in a 

 sample of glycine isolated from the proteins (Table I). The 



Table I 



Incorporation of ^^NHg^^CHg^^COOH into Proteins of Regenerating 



Rat Liver 



figures are the direct analytical values measured on the basis 

 of total carbon. No attempt has been made to degrade the 

 glycine and determine the isotope figures in each carbon 

 atom. The values show that the ratio of ^^C and ^^N excesses 

 in glycine isolated from the proteins is nearly the same as in 

 the administered compound (7- 7/7-0 and 100/100 respec- 

 tively). The value for ^*C (5-6) shows that the glycine 

 incorporated into the protein molecule has undergone slight 

 rearrangement involving rupture of the bond to the carboxyl 

 group. According to this result the administered glycine has 

 been directly incorporated into the proteins with only some 

 intermediate turnover of the carboxyl group. The glycine is 

 probably fairly well distributed in the protein molecule, and 

 we think that the isotope content of the glycine isolated from 

 the proteins can be used as a measure of the protein turnover. 

 In the polynucleotides the incorporated glycine, according 

 to earlier measurements, is probably situated in positions 4, 5 



