The Transport of S-Adenosyl-l-methionine in Isolated Yeast Vacuoles and Spheroplasts

Abstract

1 The properties of S-adenosyl-l-methionine accumulating system for both vacuoles and spheroplasts are described. Yeast vacuoles were obtained by a modified metabolic lysis procedure from spheroplasts of Saccharomyces cerevisiae. 2 Isolated vacuoles accumulate S-adenosyl-l-methionine by means of a highly specific transport system as indicated by competition experiments with sitructural analogs of S-adenosyl-lm-methionine. The S-adenosyl-l-methionine transport system shows saturation kinetics with an apparent K_m of 68 μM in vacuoles and 11 μM in spheroplasts. 3 S-Adenosyl-l-methionine accumulation into vacuoles does not require glucose, phosphoeno/pyruvic acid, ATP, ADP nor any other tri- or di-phosphorylated nucleotides. It is insensitive to azide and 2,4-dinitrophenol which strongly inhibit the glucose-dependent accumulation of Sadenosyl-l-methionine in spheroplasts. 4 The transport of S-adenosyl-l-methionine into vacuoles is optimal at pH 7.4 and is insensitive to nystatin while the uptake of S-adenosyl-l-methionine into spheroplasts is optimal at pH 5.0 and is strongly sensitive to nystatin. On this basis it has thus been possible to measure both the intracytoplasmic and the intravacuolar pool of S-adenosyl-l-methionine. 5 Our results indicate the existence of a highly specific S-adenosyl-l-methionine transport system in the vacuolar membrane which is clearly different from the one present in the plasma membrane of yeast cells.