Amino acid uptake is strongly affected during exponential growth of Saccharomyces cerevisiae in 0.7 M NaCl medium

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Labelling of Saccharomyces cerevisiae grown in 0.7 M NaCl with 35S-methionine revealed a 5–6 fold lowering of the methionine incorporation into protein, which could not be attributed solely to the approximately 50% longer generation time of cells grown in 0.7 M NaCl. Subsequent studies of the high affinity methionine uptake system showed a strongly reduced uptake of methionine during growth in 0.7 M NaCl medium. This reduced uptake was shown to be strain-independent and caused mainly by an approximately 20-fold lowered maximum velocity ( V max) of the transport system, while the substrate affinity ( K m) displayed only a minor change. A salt-instigated reduction of uptake was furthermore demonstrated for the leucine and histidine high affinity uptake systems and also for a mixture of 15 different amino acids. We therefore suggest that the reduced amino acid uptake is a general phenomenon observed in salt-grown cells.