The transport of S-adenosyl-L-methionine in isolated yeast vacuoles and spheroplasts.
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 structural analogs of S-adenosyl-L-methionine. The S-adenosyl-L-methionine transport system shows saturation kinetics with an apparent Km of 68 muM in vacuoles and 11 muM in spheroplasts. 3. S-Adenosyl-L-methionine accumulation into vacuoles does not require glucose, phosphoenolpyruvic 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 S-adenosyl-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.