64 THE PHYSIOLOGY OF PROTEIN METABOLISM 



place in the tissues, and this change in all probability is brought about 

 by the decomposition of some other amino acid with a longer carbon 

 chain. Cohn (93A) has suggested that the glycine arises in part by the 

 union of acetic acid and ammonia. Magnus-Levy, however, does not 

 consider such a synthesis very probable. 



Can a synthesis, however, of a more complex amino acid take place 

 in the same fashion? As has already been shown (p. 63) the only evi- 

 dence in favour of such a synthesis rests on a false analysis. Against 

 such a synthesis are the feeding experiments with gelatin, which lacks 

 most of the aromatic group of amino acids, and with zein, which lacks 

 glycine, lysine and tryptophane. It is impossible to use either of 

 these substances as the sole source of nitrogen for the body, and there- 

 fore we must conclude that the tissues cannot have an efficient mech- 

 anism for the conversion of lower amino acids into higher. This 

 conclusion is not quite fair, since the aromatic groups play apparently 

 a special rdle in the tissues, or the mechanism which controls their 

 breakdown (perhaps also their formation) is a specialized one, as shown 

 by the anomaly in metabolism of alkaptonuria. It is possible that 

 those proteins, which lack certain groups, are not able to form ordinary 

 tissue protein, but are able to form a protein or a protein-like body of 

 a simpler type like protamine or histone. Such a substance might 

 be retained in the tissues either as a protein reserve or as store 

 material for building up and repairing new tissue when the necessary 

 amino acids from some other source, e.g. a fresh intake of food, are 

 available. 



Formerly it was believed that Miescher's (285) experiments on the 

 Rhine salmon during their stay in fresh water at spawning time afforded 

 absolute proof of the change of simpler monamino acids into the more 

 complex diamino acid, arginine, which was required in large amount 

 for the formation of the protamine found in the genitalia of the salmon. 

 Miescher found that during the growth of the testes and ovary there was 

 a great wasting of the muscle tissue, but did not believe that it con- 

 tained sufficient preformed arginine to supply the needs of the new 

 forming protamine. Weiss (419), however, in Kossel's laboratory, de- 

 monstrated quite clearly that the salmon muscle contained an amount 

 of arginine which amply sufficed for the formation of the protamine. In 

 other words, a mere transference of arginine can occur in the body 

 without the necessity of any synthetic action. Dunlop (108) has also 

 shown that all the protein nitrogen lost by the salmon during the 

 ascent of the rivers for spawning is not required for the formation of 

 the testes and ovary. It may therefore be assumed that the whole 



