302 ADVENTURES IN RADIOISOTOPE RESEARCH 



On the phosphatide synthesis in the embryo of the chicken 



We saw that the phosphatide molecules present in the chicken's 

 embryo are not identical with those formerly located in the yolk, 

 but that they were synthesized in the embryo. The work of Schonheimer 

 and RiTTENBERG [1936] gives us important information about the units 

 which are utilized in the synthesis. They found, by making use of deute- 

 rium as an indicator, that the developing hen's egg forms no new fatty 

 acids and their result excluded also the possibility that unsaturated 

 fatty acids present in the egg had been hydrogenated during develop- 

 ment. Needham [1931], on the other hand, found that a marked desatu- 

 ration occurs in an aqueous emulsion of embryonic tissues mixed with 

 the corresponding yolk and vigorously shaken. The embryo must thus 

 make use of the fatty acids present in the yolk to build up its phosphati- 

 des: in doing this it possibly gives some preference to the less saturated 

 fatty acids. The fatty acid components of the phosphatides extracted 

 from the embryo are found to be less saturated than those extracted 

 from the yolk residue. This, at first sight puzzling fact that the embryo, 

 instead of using the phosphatide molecules found in great abundance 

 in the yolk synthesizes its own phosphatide molecules, becomes less 

 puzzling when we envisage the likely possibility that the synthesis of 

 phosphatide molecules is a step in other chemical processes which 

 occur simultaneously in the growing embryo. 



Summary 



Radioactive sodium phosphate was injected into lien's eggs which were then 

 incubated in some experiments for 6, and in others for 11, 16 and 18 days. While 

 the phosphatide -phosphorus extracted from the embryo always showed a high 

 specific activity (activity per mgm P), that extracted from the yolk was hardly 

 active at all. The phosphatide molecules present in the embryo could not there- 

 fore have been taken from the yoUi only, but must have been sjTithesized in the 

 embryo. The investigation of the "acid-soluble" and residual (mainly nucleoprotein) 

 phosphorus extracted from the embryo led to a similar result — namely, that 

 the ratio in which the labelled inorganic phosphorus atoms are incorporated 

 into the different phosphorus compounds present in the embryo is governed 

 solely by probability considerations. Practically all the phosphorus atoms present 

 in the various compounds of the embryo must pass through the stage of inorganic 

 P; only the inorganic phosphorus present in the embryo is taken as such from 

 the yolk or the white. 



In some experiments, instead of radioactive sodium phosphate, labelled hexo- 

 semonphosphate was injected into the egg before incubation. The hexosemono- 

 phosphate-phosphorus extracted from the embryo had about the same specific 

 activity as the inorganic and the phosphatide phosporus extracted. This result 

 suggests that inorganic phosphate radicals which were split off from the hexo- 

 semonphosphate and from other compounds present in the yolk and the white, 

 rather than the hexosomonophosphate molecules introduced into the latter, are 

 utilized to build up the phosphorus compounds of the chicken's embryo. 



