SULFATE TRANSPORT IN THE CYANOBACTERIUM SYNECHOCOCCUS R-2 (ANACYSTIS-NIDULANS, S-LEOPOLIENSIS) PCC-7942

Synechococcus R-2 (PCC 7942) actively accumulates sulphate in the ligh t 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: pH(o), 7.5; [SO42-](o), 0.304 mol m(-3)). The sulphate transpor ter is different from that found in higher plants: it appears to be an ATP-driven pump transporting one SO42-/ATP [Delta mu SO4i,o2- = + 27. 7 +/- 0.24 kJ mol(-1) (light) and + 24 +/- 0.34 kJ mol(-1) (dark)]. Th e rate of metabolism of SO42- at pH(o) 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 potassi um, proton, sodium or chloride transport. The alga has a constitutive over-capacity for sulphate uptake [light (n = 105): K-m = 0.3 +/- 0.1 mmol m(-3), V-max = 1.8 +/- 0.6 nmol m(-2) s(-1); dark (n = 56): K-m = 1.4 +/- 0.4 mmol m(-3), V-max = 41 +/- 22 pmol m(-2) s(-1)]. Sulphite (SO32-) was a competitive inhibitor of sulphate uptake. Selenate (SeO 42-) was an uncompetitive inhibitor.