126 H. R. Mahler, H. Walter, A. Bulbenko and D. W. Allmann 



of protein, but solely suggest that there may not be free equilibration between 

 the free added amino acid pool and amino acids formed and utilized metaboli- 

 cally during precursor protein breakdown and product protein formation 

 respectively. 



Another potentially very fruitful line of investigation is provided by some 

 experiments of Ebert's, the results of which tentatively suggest the incorporation 

 of organ specific adult proteins into those of embryos subsequent to chorio- 

 allantoic grafts of the donor organs (3, 13). These researches were the out- 

 growth of findings by Murphy (14) and by Danchakoff (15), made some 

 forty years ago, that such transplants of adult chicken spleen lead to a specific 

 enlargement of the host organs. A systematic re-investigation of the phenomenon 

 by Weiss led to the conclusion that transplants of kidney and liver, as well 

 as injections of organ breis of six-day old chick embryos into four-day old 

 hosts, could lead to similar effects (2). Weiss correctly pointed out that experi- 

 ments of this sort did not permit a choice between a 'template' or a 'specific 

 precursor' type of mechanism. Ebert's investigations are designed to shed 

 some light on this question as well as on the more general ones of protein 

 synthesis and organ specific growth control in embryonic development. 



In our own investigations we have made use of S^^-labeled organ homo- 

 genates, isolated proteins, peptides, and amino acids to gain some insight into 

 the pattern of embryonic protein biosynthesis. In this work we have been 

 interested not only in the immediate but also in the original precursors, which 

 in this case must consist of all or part of the egg white and yolk proteins. 

 Preliminary accounts of some aspects of this work have appeared (16). 



II. METHODS AND RESULTS 



1 . Preparation oj Labeled Precursors 



In the experiments to be reported in tliis and subsequent sections S^^- 

 labeled proteins, peptides, and a mixture of amino acids were prepared bio- 

 synthetically as follows: Torulopsis utilis was grown on S^^-sulfate (obtained 

 from Oak Ridge National Laboratory), according to Wood and Perkinson. (17) 

 After extraction with organic solvents (18) the yeast protein was hydrolysed 

 with a 1 :1 mixture of 6N HCl and 90 per cent fomiic acid. Humin was removed 

 by centrifugation and a portion of the neutralized hydrolysate, which also 

 served as source of amino acids in the experiments to be reported, corresponding 

 to 50 mc of the original S^^, was injected intraperitoneally into a laying White 

 Leghorn hen in two doses, about five hours apart. Eight hours after the second 

 injection the blood was withdrawn by heart puncture, allowed to clot, and serum 

 albumin and serum globulin prepared (19). The oviduct was removed from 

 the hen, and ovalbumin prepared essentially as described by Steinberg and 

 Anfinsen (11). All proteins were treated with cysteine at a pH of 8.0 to 8.5 

 to assure removal of exchangeable S^^, and then dialysed. Peptides were 

 prepared by peptic hydrolysis of the proteins. Aliquots of the radioactive 

 amino acids, peptides, and proteins were prepared by standard methods and 

 counted. In the tracer experiments, 0.05 to 0.1 ml aliquots of the radioactive 

 precursor solutions, containing 0.3 to 1.8 mg and 6000 to 25,000 counts per 

 minute each, were injected into the yolk or the albuminous portion of some two 



