116 THE BIOSYNTHESIS OF PROTEINS 



nucleotide-peptide compounds has been reported from several laboratories. 

 Ascites tumour cells contain aspartic acid associated with a uridylic nucleo- 

 tide (Reith, 1956), and chicken liver a compound tentatively described as 

 adenosinediphosphoglutamic acid (Hansen and Hageman, 1956). Several 

 compounds containing a few amino acids were isolated from micro-organ- 

 isms (Hase et al, 1959; Brown, 1959). The peptide linked nucleotides 

 which were detected in yeast (Koningsberger et al., 1957; Harris and 

 Davies, 1958; Koningsberger, 1960) and in liver (Szafranksi et al., 1959, 

 1960; Steinberg et al., 1960) might be of special interest, for the terminal 

 carboxyl of the peptide moiety reacts with hydroxylamine. The com- 

 pounds might thus be activated peptides acting as intermediates in some 

 anabolic process. The chemical structure of some of the compounds from 

 yeast has now been established (Davies and Harris, 1960). They are mixed 



HN:C-NH2 HN-.C-NHj 



NH NH 



CH2 ^^2 



CH, CHp CH3 CH 



°' CHa'O'P-OCO-CHNHCOCHNHCOCH NHC0CH-NH2 

 OH 



Fig. 30. Structure of a nucleopeptide from yeast (Davies and Harris, 



1960). 



anhydrides in which the terminal carboxyl of the peptide is condensed 

 with the 5' phosphate group of the uridylic moiety of a dinucleotide (Fig. 

 30). Some of these compounds are extracted only by cold acid treatment, 

 as if they were weakly bound to other cell constituents in neutral extracts. 

 One may wonder whether the peptides found in yeast by Turba and Esser 

 (1955) have the same origin. 



The uridylic acid peptide compounds discovered by Parks (1952), and 

 other clearly related substances (Strominger and Threnn, 1959; O'Brien 

 and Zilliken, 1959) have not been mentioned here, because they are known 

 to be precursors of bacterial cell wall. This serves to remind one that 

 amino acids and peptides are found in other substances beside proteins, 

 and that nucleotide-peptide compounds might have nothing to do with 

 protein synthesis. However, until their function is discovered, they must 



