13 



Enzymatic and Nonenzymatic Synthesis in 



Adenyl Tryptophan 1 



MARVIN KARASEK PAUL CASTELFRANCO 2 



P. R. KRISHNASWAMY ALTON MEISTER 



Department of Biochemistry, Tufts University School of Medicine 



Acyl adenylates have been postulated as intermediates in the activation of 

 acetate [1] and of fatty acids [2, 3], as well as in the synthesis of phenylacetyl- 

 glutamine and hippurate [4]. Thus, the activation of acetate and of phenylace- 

 tate may be represented as follows: 3 



Acetate + ATP ±± Acetyl-AMP + PP 

 Phenylacetate + ATP ^± Phenylacetyl-AMP + PP 



The activation of amino acids, which has been observed with several enzyme 

 preparations, appears to involve an analogous reaction [5, 6, 7, 8] : 



Amino acid + ATP *± Aminoacyl-AMP + PP 



This reaction has been followed by observing the formation of amino acid hy- 

 droxamate when enzyme preparations are incubated with amino acid, mag- 

 nesium ions, adenosine triphosphate, and high concentrations of hydroxylamine. 

 The reaction has also been observed by determining the rate of exchange of 

 radioactive inorganic pyrophosphate with adenosine triphosphate in the pres- 

 ence of magnesium ions, amino acid, and enzyme. 



That the intermediate formed in the activation of amino acids is an aminoacyl 

 adenylate of the type (fig. 1) postulated to occur in other systems [1-4] is sug- 

 gested by several observations. For example, synthetic acyl adenylates are 



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. 



3 Abbreviations: adenosine triphosphate, ATP; adenylic acid, AMP; pyrophosphate, PP. 



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