948 



ADVENTURES IN RADIOISOTOPE RESEARCH 



While we measure the rate of renewal of phosphatide molecules with 

 respect to their phosphate content by employing ^ap as an indicator, 

 the rate of renewal of the fatty acid constituents is determined by the 

 use of deuterium^*^-' as indicator, and the new-formation of the choline 

 content by applying i^N as a tracer^*^^*. A molecule can clearly be 

 renewed in various ways. 



SITE OF FORMATION OF PHOSPHORUS COMPOUNDS IN THE 



ORGANISM 



Origin of Yolk Phosphatides 



We shall first consider the site of formation of some constituents of 

 the hen's egg. Where in the organism are the phosphatides found in 

 the yolk synthesized ? This question can be answered by comparing the 

 specific activity of phosphatide P extracted from the yolk and from the 

 different organs a few hours after administration of labelled sodium 



phosphate^®*\ 



The results of an experiment in which the hen was killed 5 hours after 

 subcutaneous injection of labelled P are seen in Table 6. The specific 

 activities of the yolk phosphatide and the ovary phosphatide P were 



Table 6. — Specific Activity of Phosphatides 

 Extracted from the Organs of a Hen 



Organ 



Relative specific 



activity (Activity 



of inorganic 



plasma P = 1) 



Liver . . . 

 Plasma . . 

 Ovary . . . 



Yolk .... 

 Intestine 

 Spleen . 



0.54 



0.43 



0.039 



0.0035 



0.11 



0.1 



very low, showing that only a small part of the molecules present 

 in the said phosphatides had been formed within the last 5 hours. 

 The plasma phosphatide P had a much higher specific activity than 

 those extracted from the ovary and the yolk, while the liver phosphatide 

 P had a higher specific activity than the plasma phosphatide P. The 

 gradient indicating the presence of phosphatide molecules formed within 

 the last 5 hours, thus falls off in the direction from the liver, through 

 the plasma, into the ovary. 



