14 



Participation of Adenyl Amino Acids in Amino 

 Acid Incorporation into Proteins 1 



PAUL CASTELFRANCO - ALTON MEISTER KIVIE MOLD AVE 



Department of Biochemistry, Tufts University School of Medicine 



It has been postulated that aminoacyl adenylates possessing the general struc- 

 ture shown in figure 1 are formed in the enzymatic activation of amino acids 



HO 

 i ii ii 



R-C-C-O-P- 0-Ribose-Adenine + 



I i 



NH 3 + 0" 



Fig. 1 



by adenosine triphosphate, and that such "activated amino acids" are inter- 

 mediates in the incorporation of amino acids into microsomal proteins observed 

 in cell-free systems [1, 2]. Whether such incorporation represents protein syn- 

 thesis is not yet known, although this hypothesis has indeed been considered. 

 Recent studies in our laboratory have been directed toward a better under- 

 standing of the activation of amino acids and the possible role of aminoacyl 

 adenylates in amino acid incorporation into protein. In the preceding paper 

 by Karasek et al. [3], evidence for the net synthesis of tryptophanyl adenylate 

 by a purified tryptophan-activating enzyme is described. These observations 

 appear to give direct support to the idea that aminoacyl adenylates are the 

 initial products of the activation reaction. The subsequent reactions of ami- 

 noacyl adenylates are not yet clearly understood, although it has been sug- 

 gested that the amino acid moieties of such anhydrides are transferred to pro- 

 tein via specific acceptors, possibly ribonucleic acid [4]. 



1 Supported in part by research grants from the National Science Foundation and the 

 National Institutes of Health, Public Health Service. 



2 Postdoctorate fellow of the National Heart Institute, Public Health Service. 



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