Formation 5'-ethylthioadenosine from DL-ethionine in yeast.

Experiments on the formation of adenine thiomethylriboside from methionine in yeast (1) suggested a study of ethionine as a source of organic sulfur in the growth medium. The sulfur atom of this amino acid analogue is not utilized for the formation of thiomethyladenosine (2). However, we found in extracts of yeast (Torulopsis utilis and Saccharomyces cerevisiae) grown in the presence of an excess of nL-ethionine another nucleoside which seemed to be closely related to thiomethyladenosine. Besides showing the typical ultraviolet absorption spectrum of an adenine compound, it contained sulfur and gave a nitroprusside reaction like that of methionine, ethionine, or thiomethyladenosine (3). The differences in the RF values on paper chromatograms precluded the possibility that the new compound was identical with thiomethyladenosine. It appeared probable that ethylthioadenosine could be formed when ethionine was present in the growth medium. The isolation of this substance in quantity and its analytical examination corroborated this assumption.