Cysteine Uptake for Accumulation of Glutathione by the Cyanobacterium Synechocystis strain PCC 6803

By incubation with precursor amino acids, L-glutamate, L-cysteine, and glycine, or with L-cysteine, the unicellular cyanobacterium Synechocystis strain PCC 6803 increased intracellular glutathione levels, under illumination with white light. L-Cystine could not serve as the precursor. Two transport systems for L-cysteine were evident in the strain: a high (Ks; L-cysteine concentration giving one-half of the maximum uptake, 21~35 μM) and a low (Ks, 1.0~1.8 mM) affinity transport system. The latter, responsible for glutathione accumulation, was an energy-requiring process. L-Cysteine uptake by the two transport systems were Na(+)-independent, and inhibited by the presence of neutral amino acids and less inhibited by basic or acidic amino acids. These results suggested that the neutral amino acid symport(s) is involved in L-cysteine uptake for the GSH accumulation in this strain.