¹ From the Department of Agricultural and Biological Chemistry, Pennsylvania State University, University Park.

Dr. Fisher's present address is Wyeth Institute for Medical Research, Philadelphia

Two unknown radioactive areas appeared after radioautography and two dimensional paper chromatography of culture medium in which Escherichia coli was grown. These materials were studied by paper chromatography and paper electrophoresis of several derivatives and identified as ethionine and ethionine sulfone, the latter an artifact. Chromatographic coincidence of the unknowns and their derivatives with authentic materials establishes the identification.

Ethionine was found in cellular extracts and in the growth media of Escherichia coli, Bacillus megaterium, Pseudomonas aeruginosa, and Aerobacter aerogenes but not in Scenedesmus, Saccharomyces cerevisiae, or bovine lymphosarcoma cells.

Ethionine was synthesized by resting E. coli cultures from radioactive sulfate and from radioactive methionine. Growing cells labeled ethionine within 1 minute after addition of radioactive sulfate to cultures. Levels of radioactivity in ethionine increased with time. No incorporation of this amino acid could be detected in the cellular proteins formed under the conditions of this study.

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