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 structural analogs of S-adenosyl-L-methionine. The S-adenosyl-L-methionine transport system shows saturation kinetics with an apparent K , of 68 pM in vacuoles and 11 pM 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 Sadenosyl-L-methionine in spheroplasts.4. The transport of S-adenosyl-L-methionine into vacuoles ic 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.

Uptake of adenosylmethionine and related sulfur compounds by isolated rat liver

“…It is worth noting, in this respect, that primitive eukaryotes, i.e., yeast cells, bear a simila; transport system, but with higher affinity towards SAM [21] . -The inhibition of SAM uptake observed in the liver by 2,4dinitrophenol suggests that the system is energydependent, similarly to what has been already shown with spheroplasts of Sacchuromyces cerevisiae [4] .…”

“…An active transport system with high affinity towards SAM has been described in yeast cells, which accumulate very peculiarly the sulfonium compound into the vacuoles [3,4] ; furthermore mutants lacking this transport system have been isolated [3] . The uptake of SAM by rat pancreas isolated cells [ 51 as welI as rabbit erythrocytes [6] has also been studied.…”

Dynamic aspects of vacuolar and cytosolic amino acid pools of Saccharomyces cerevisiae

“…Wiemken and collaborators (6,15,16) discovered that the vacuoles in Candida utilis and Saccharomyces cerevisiae contain specific pools of basic amino acids, from which most acidic and neutral amino acids are excluded. These findings indicated that vacuoles are metabolically active organelles and must have differential sequestration systems for certain amino acids (2) and other metabolites (11).…”

The Yeast Vacuolar Membrane Proteome

“…However, based on measurements of transport activities across the vacuolar membrane and determination of organic substance content in the vacuole lumen, the existence of many more proteins with translocation activities is expected. Transport systems for S-adenosylmethionine (15), purines (16), polyamines (17), and sulfate (18) have been postulated based on activity measurement, but the identity of the corresponding proteins has remained elusive.…”