BASIC BIOCHEMICAL QUESTIONS 



There are good indications for the assumption that the 

 carboxy-activated amino acids enter directly into the mech- 

 anism of sequential arrangement (8,22,24). Furthermore, the 

 amino acids may enter as an amino acid'^P-nucleoside. The 

 activated amino acid seems, however, to approach the assembly 

 line not isolated but still fixed to the amino acid specific enzyme 

 protein (11). As a first approximation to a mechanism, we then 

 consider a specific enzyme for each amino acid which as a war- 

 head carries the amino acid linked to the phosphoryl of a mono- 

 nucleotide, eventually to effect selective linking into chains. 



There is, on the other hand, a certain likelihood that the 

 amino acid chain is deposited and grows along on ribonucleic 

 acid. The incorporation of radioactive amino acids takes place 

 in special microsomes rich in nucleic acid (4,24). Recent ob- 

 servations (14) have indicated that the microsome carrying out 

 amino acid synthesis contains approximately equal amounts of 

 nucleic acid and protein. This observation seems to counter- 

 indicate a nucleoprotein as responsible for the direction of the 

 amino acids into sequences. The amount of protein would be 

 too small to permit such an interpretation. But the particular 

 activated amino acid approaches the assembly line in association 

 with its specific enzyme. An enzyme-mononucleotidc'^amino 

 acid might react with a specific nucleic acid which by its own 

 sequential arrangement of nucleotides is supposed to direct the 

 sequential patternization of a protein. 



One process of progressive chain elongation has been suc- 

 cessfully analyzed, namely, fatty acid synthesis (17). It ap- 

 peared in that case that chain elongation always occurred be- 

 tween two activated molecules. But the energy of only one 

 energy-rich link is utilized, namely, the thioester bond to the 

 carboxyl which enters the • COCH2 • link. To compare this 

 methyl-carboxyl linking to the amino-carboxyl linking in a pep- 

 tide is not too far fetched, since it has been found (6) that the 

 methylene-carbonyl bond is hydrolyzed by chymotrypsin, which 

 makes the biochemical comparison between • CO — CH2 • and 

 • GO — NH • linking rather plausible. The importance of this 



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