TURNOVER OF PHOSPHATIDES 



355 



consider that in contrast to the present autliors, lliey investigated lasting 

 rats. Platt and Porter (1947), when comparing the turnover of plios- 

 phatides in the liver of fed and fasting rats, found the former value to 

 be about 1/3 larger than the latter. That the diet influences the percentage 

 renewal of liver phosphatides of the rat was also shown recently by 

 Campbell and Kosterlitz (1948). 



While we cannot calculate turnover rates from 1h(> ratio of the speci- 

 fic activities of the phosphatide P and total liver P, this ratio indicates 

 to what extent phosphatide P atoms are renewed compared with the 

 average total P atoms. We listed these ratios in Tabk; 4 along witli the 

 total P content of the livers investigated. We have not listed the inor- 

 ganic P nor the phosphatide P contents as we were interested primarily 

 in phosphatide P and inorganic P fractions of high purity and the ex- 

 tended purification processes entailed an appreciable loss. 



The absolute amount of phosphatides renewed during a given span 

 of time increases, in contrast to the percentage renewal, with the age 

 of the rat, as both the weight of the liver and its phosphatide content 

 are increasing with age. The phosphatide content of the liver of the 



Table 3. — Lower Limit of the Percentage Turnover per 

 Hour of the Phosphatides of the Rat Liver. Inorganic 



P Scale 



Table 4. — Specific Activity of Liver Phosphatides as 

 Percentage of the Specific Activity of the Total P of 



the Liver 



23* 



