Evidence for two calcium transport systems in the photosynthetic bacteriumChromatium vinosum

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Abstract
Light‐dependent Ca2+efflux via the Ca2+/H+antiport in the photosynthetic purple sulfur bacteriumChromatium vinosumwas inhibited by three phenothiazines: chlorpromazine; trifluoperazine and phenothiazine. The inhibitors had no effect on Ca2+uptake byC. vinosumin the dark nor any effect on the light‐dependent efflux of either Na+or Tl+catalyzed, respectively, by theC. vinosumNa+/H+or K+/H+antiports. Ruthenium red and LaCl3, neither of which inhibited light‐dependent Ca2+efflux inC. vinosum, markedly inhibited Ca2+uptake in the dark byC. vinosumcells. Ruthenium red had no effect on the uptake of either Na+or the K+analog T1+byC. vinosumcells in the dark. These results have been interpreted in terms of two separate Ca2+transport systems inC. vinosum: (i) a phenothiazine‐sensitive and ruthenium red, La3+‐insensitive Ca2+/H+antiport responsible for Ca2+efflux in the light; and (ii) a ruthenium red and La3+‐sensitive but phenothiazine‐insensitive Ca2+uptake system.