5-CARBOXYMETHYLURIDINE A NOVEL NUCLEOSIDE DERIVED FROM YEAST AND WHEAT EMBRYO TRANSFER RIBONUCLEATES

A carboxyl-containing nucleoside, 5-carboxymethyluridine, has been isolated from the transfer ribonucleates of bakers’ yeast, brewers’ yeast, and wheat embryo. The 2′- and 3′-nucleotides of 5-carboxymethyluridine were isolated from alkali hydrolysates of the purified transfer ribonucleate preparations. A phosphodiesterase hydrolysate of wheat embryo transfer ribonucleates was examined for the presence of 5- carboxymethyluridine 5′-phosphate, but none could be detected. However, after alkali treatment of the 5′- nucleotides produced by the action of phosphodiesterase on wheat embryo transfer ribonucleates, a compound having the properties of the 5′-nucleotide of 5-carboxymethyluridine was isolated. This observation suggests that 5-carboxymethyluridine does not occur as the free acid in native transfer ribonucleates, but that before alkali hydrolysis the carboxyl function is substituted by an alkali-labile group. One possibility is that 5-carboxymethyluridine may occur as a saponifiable carboxymethyl ester in native transfer ribonucleates. The base derived from 5-carboxymethyluridine was identical with synthetic 5-carboxymethyluracil, and distinctly different from 6-carboxymethyluracil, in its spectral, electrophoretic, and chromatographic properties. 5-Carboxymethyluridine 2′(3′)-phosphate accounts for 0.34 and 0.15 mole % of the products formed by alkali hydrolysis of transfer ribonucleates from brewers’ yeast and wheat embryo, respectively. © 1968, American Chemical Society. All rights reserved.