Sulphate transport in the cyanobacterium Synechococcus R-2 (Anacystis nidulans, S. leopoliensis) PCC 7942 |
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Authors: | R J RITCHIE |
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Institution: | Biology A-12, School of Biological Sciences, The University of Sydney. NSW 2006, Australia |
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Abstract: | Synechococcus R-2 (PCC 1942) actively accumulates sulphate in the light and dark. Intracellular sulphate was 1.35 ± 0.23 mol m?3 (light) and 0.894 ± 0.152 mol m?3 (dark) under control conditions (BG-11 media: pHo, 7.5; SO42?]o, 0.304 mol m?3). The sulphate transporter is different from that found in higher plants: it appears to be an ATP-driven pump transporting one SO42?/ATP ΔμSO42?i,o=+ 27.7 ± 0.24 kJ mol?1 (light) and + 24 ± 0.34 kj mol?1 (dark)]. The rate of metabolism of SO42?at pHo, 7.5 was 150 ± 28 pmol m?2 s?1 (n = 185) in the light but only 12.8 ± 3.6 pmol m?2 s?1 (n = 61) in the dark. Light-driven sulphate uptake is partially inhibited by DCMU and chloramphenicol. Sulphate uptake is not linked to potassium, proton, sodium or chloride transport. The alga has a constitutive over-capacity for sulphate uptake light (n= 105): Km= 0.3 ± 0.1 mmol m?3, Vmax, = 1.8 ± 0.6 nmol m?2 s?1; dark (n= 56): Km= 1.4 ± 0.4 mmol m?3, Vmax= 41 ± 22 pmol m?2 s?1]. Sulphite (SO32?) was a competitive inhibitor of sulphate uptake. Selenate (SeO42?) was an uncompetitive inhibitor. |
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Keywords: | cyanobacteria electrochemical gradient inhibitors K+ membrane potential Na+ pH SO42? |
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