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Metabolism of Ethionine in Ethionine-Sensitive and Ethionine-Resistant Cells of the Enteric Yeast Candida slooffii¹

^a Departamento de Microbiologia Geral, Instituto de Microbiologia, Universidade Federal do Rio de Janeiro, Rio de Janeiro, GB, Brasil

ABSTRACT

In a defined medium with added ethionine plus low methionine, phenylalanine, tryptophan, tyrosine, adenine, and additional methionine reversed inhibition of the enteric yeast Candida slooffii by ethionine. Isoleucine and 7-methylguanine restored half-maximal growth. Choline but not triethylcholine inhibited C. slooffii. 6-Mercaptopurine reversed ethionine inhibition and also synergistic inhibition by ethionine plus choline. Protection against ethionine by adenine plus aromatics was also evident with log-phase cells in the absence of methionine. Incorporation of ethionine-ethyl-1-¹⁴C by resting cells was partially inhibited by aromatic amino acids and methionine. Ethionine depressed incorporation of ³H-phenylalanine but not of ³H-adenine. Ethionine-resistant mutants were isolated which incorporated ethionine efficiently and degraded it to yet unidentified substances not including 5'-ethylthioadenosine. Ethionine-sensitive cells accumulated more S-adenosylethionine (SAE) than resistant mutants. Adenine was a good precursor of SAE. Radioactivity from ethionine-ethyl-1-¹⁴C was recovered from cell fractions of ethionine-sensitive cells with the following distribution: cold trichloroacetic acid-soluble > hot trichloroacetic acid-insoluble > lipids > deoxyribonucleic acid > ribonucleic acid. Total radioactivity recovered from ethionine-sensitive cells was twice as much as that from ethionine-resistant mutants.

¹ Taken in part from a thesis submitted by the senior author in partial fulfillment of the requirements for the D.Sc. degree in Microbiology. A preliminary communication was presented at the Brazilian Academy of Sciences, 1969 (An. Acad. Brasil. Ciênc. 4:650R-651R).