SECTION 9 



PROTEIN METABOLISM 



9-1. The Structure of the Avian Egg-proteins before and after 

 Development 

 The hen's egg contains at the beginning of development, as we 

 have already seen, about six or seven different proteins and a number 

 of smaller nitrogenous molecules. At the end it consists of another 

 set of proteins, mostly the avian body and serum proteins, a further 

 collection of simpler nitrogenous substances, differently distributed, 

 and, in addition, a quantity of incombustible protein breakdown 

 products, the outcome of the embryonic oxidations. How does the 

 constitution (especially as to amino-acid distribution) of the original 

 egg-protein molecule differ from that of the finished embryo-protein 

 molecule? One answer is afforded by the work of Plimmer & 

 Lowndes who massed together the proteins at o, 15 and 21 days of 

 incubation, and made van Slyke estimations of the amino-acid dis- 

 tribution, employing Plimmer's modifications of this technique. In 

 Table 130 are shown the results, expressed in percentages of the total 

 nitrogen. 



Table 130. 



Plimmer and Lowndes' figures (massed proteins) : 



