Transport of S-Adenosylmethionine in Saccharomyces cerevisiae

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RESUMO

The properties of a specific system for the transport of S-adenosylmethionine in yeast are described. The process was pH-, temperature-, and energy-dependent, and showed saturation kinetics. The Km for the system was 3.3 × 10−6m. Of the S-adenosylmethionine moieties tested, only S-adenosylhomocysteine competitively inhibited the uptake of the adenosylsulfonium compound. Adenine, adenosine, methionine, homocysteine, and the sulfonium compound S-methylmethionine were without effect. The analogue S-adenosylethionine showed competitive inhibition. Under conditions of inhibition of protein synthesis by cycloheximide or methionine starvation, permease activity was stable. The mutant sam-p3 apparently was able to transport S-adenosylmethionine only by diffusion. Uptake by diploids containing this mutation was directly proportional to the gene dose.

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