STRUCTURAL AND CHEMICAL ARCHITECTURE OF HOST CELLS 



159 



Other related reactions have been summarized by Romberg (1957b). Of 

 these the most important include the formation of active metliionine, or 

 S-adenosylmethionine, first described by Cantoni (1953), in a reaction 

 liberating P from the terminal group of ATP and pyrophosphate from the 

 innermost phosphates of the nucleotide (Cantoni and Durell, 1957). The 

 details of tliis complex reaction are presented in formula (XV), and 



COOH 

 i 



CHNH2 



s- 



I 



CH3 



Adenine 



I . 

 C ^O 



I 

 (CHOH)2 



I 



HC 



Adenine 



c— O 



.0 



P O 



I ////// I 



CH2O-P-O-P-O-P-OH +S 



COOH 



I 

 CHNH2 



CHj (CHOH)2 



I I 



CH2 HC 



■CH2 



OH 

 3 



OH 

 2 



OH 

 1 



CH, 



methionine 



" active methionine" 

 (XV) 



P P 

 // // 



+ H3PO4 + HO-P-O-P-OH 



OH 

 2 



OH 

 3 



have not yet been thoroughly clarified. However, active methionine embody- 

 ing a methyl sulfonium group of high group -transfer potential is now recog- 

 nized to be an active methyl donor in the formation of a wide variety of 

 N- and S-methyl-containing compounds, as in the reaction to form creatine 

 shown in formula (XVI). 



CH2COOH 



HN 



I 



C=NH 



NH2 



gnanidoacetic 

 acid 



"Active methionine" 

 S— adenosyimethionine 



CHjCOOH 



CH3N 



1 



C=NH 



I 



NHj 



Creatine 



S-adenosyl 

 homocysteine 



(XVI) 



In the formation of tryptophan and histidine, reactions have recently been 

 described whereby pyrophosphoryl ribose-5-phosphate participates in the 

 formation of the indole and imideazole rings, respectively. Yanofsky (1957) 

 has demonstrated a series of reactions, beginning with this compound and 

 anthranilic acid, as shown in formula (XVII). 



VOL. I — 12 



