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Kinetics of chloride transport in the cyanobacterium Synechococcus R‐2 ( Anacystis nidulans, S. leopoliensis ) PCC 7942
Author(s) -
RITCHIE R. J.
Publication year - 1992
Publication title -
plant, cell and environment
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.646
H-Index - 200
eISSN - 1365-3040
pISSN - 0140-7791
DOI - 10.1111/j.1365-3040.1992.tb01471.x
Subject(s) - kinetics , chemistry , synechococcus , chloride , nuclear chemistry , cyanobacteria , sodium , analytical chemistry (journal) , chromatography , bacteria , biology , physics , organic chemistry , quantum mechanics , genetics
The kinetics of the light‐driven Cl − uptake pump of Synechococcus R‐2 (PCC 7942) were investigated. The kinetics of Cl − uptake were measured in BG‐11 medium (pH o , 7·5; [K + ] o , 0·35 mol m −3 ; [Na + ] o , 18 mol m −3 ; [Cl − ] o , 0·508 mol m −3 ) or modified media based on the above. Net 36 Cl − fluxes (ϕCl − o,i ) followed Michaelis‐Menten kinetics and were stimulated by Na + [18 mol m −3 Na + BG‐11 ϕCl − max = 3·29±0·60 (49) nmol m −2 s −1 versus Na + ‐free BG‐11 ϕCl − max = 1·02±0·13 (54) nmol m −2 s −1 ] but the Km was not significantly different in the presence or absence of Na + at pH o 10; the Km was lower, but not affected by the presence or absence of Na + [Km = 22·3±3·54 (20) mmol m −3 ]. Na + is a non‐competitive activator of net ϕCl − o,i . High [K + ] o (18 mol m −3 ) did not stimulate net ϕCl − o,i or change the Km in Na + ‐free medium. High [K + ] o (18 mol m −3 ) added to Na + BG‐11 medium decreased net ϕCl − o,i [18 mol m −3 K + BG‐11; ϕCl − max = 2·50±0·32 (20) nmol m −2 s −1 versus BG‐11 medium; ϕCl − max = 3·35±0·56 (20) nmol m −2 s −1 ] but did not affect the Km 55·8±8·100 (40) mmol m −3 ]. Na + ‐stimulation of net ϕCl − o,i followed Michaelis‐Menten kinetics up to 2–5 mol m −3 [Na + ] o but higher concentrations were inhibitory. The Km for Na + ‐stimulation of net ϕCl − o,i [K 1/2 (Na + )] was different at 47 mmol m −3 [Cl − ] o (K 1/2 [Na + ] = 123±27 (37) mmol m −3 ]. Li + was only about one‐third as effective as Na + in stimulating Cl − uptake but the activation constant was similar [K 1/2 (Li + ) = 88±46 (16) mmol m −3 ]. Br − was a competitive inhibitor of Cl − uptake. The inhibition constant (Ki) was not significantly different in the presence and absence of Na + . The overall Ki was 297±23 (45) mmol m −3 . The discrimination ratio of Cl − over Br − (δCl − /δBr − ) was 6·38±0·92 (df = 147). Synechococcus has a single Na + ‐stimulated Cl − pump because the Km of the Cl − transporter and its discrimination between Cl − and Br − are not significantly different in the presence and absence of Na + . The Cl − pump is probably driven by ATP.