TY - JOUR
T1 - Binding affinity of bicarbonate and formate in herbicide-resistant D1 mutants of Synechococcus sp. PCC 7942
AU - Cao, J.
AU - Ohad, N.
AU - Hirschberg, J.
AU - Xiong, J.
AU - Govindjee,
PY - 1992/12
Y1 - 1992/12
N2 - We examined the effects of mutations at amino acid residues S264 and F255 in the D1 protein on the binding affinity of the stimulatory anion bicarbonate and inhibitory anion formate in Photosystem II (PS II) in Synechococcus sp. PCC 7942. Measurements on the rates of oxygen evolution in the wild type and mutant cells in the presence of different concentrations of formate with a fixed bicarbonate concentration and vice versa, analyzed in terms of an equilibrium activator-inhibitor model, led to the conclusion that the equilibrium dissociation constant for bicarbonate is increased in the mutants, while that of the formate remains unchanged (11±0.5 mM). The hierarchy of the equilibrium dissociation constant for bicarbonate (highest to lowest, ±2 μM) was: D1-F255L/S264A (46 μM)>D1-F255Y/ S264A (31 μM)≈D1-S264A (34 μM)≈D1-F255Y (33 μM)>wild type (25 μM). The data suggest the importance of D1-S264 and D1-F255 in the bicarbonate binding niche. A possible involvement of bicarbonate and these two residues in the protonation of QB-, the reduced secondary plastoquinone of PS II, in the D1 protein is discussed.
AB - We examined the effects of mutations at amino acid residues S264 and F255 in the D1 protein on the binding affinity of the stimulatory anion bicarbonate and inhibitory anion formate in Photosystem II (PS II) in Synechococcus sp. PCC 7942. Measurements on the rates of oxygen evolution in the wild type and mutant cells in the presence of different concentrations of formate with a fixed bicarbonate concentration and vice versa, analyzed in terms of an equilibrium activator-inhibitor model, led to the conclusion that the equilibrium dissociation constant for bicarbonate is increased in the mutants, while that of the formate remains unchanged (11±0.5 mM). The hierarchy of the equilibrium dissociation constant for bicarbonate (highest to lowest, ±2 μM) was: D1-F255L/S264A (46 μM)>D1-F255Y/ S264A (31 μM)≈D1-S264A (34 μM)≈D1-F255Y (33 μM)>wild type (25 μM). The data suggest the importance of D1-S264 and D1-F255 in the bicarbonate binding niche. A possible involvement of bicarbonate and these two residues in the protonation of QB-, the reduced secondary plastoquinone of PS II, in the D1 protein is discussed.
KW - (Synechococcus sp. PCC 7942)
KW - D1 protein
KW - Photosystem II
KW - bicarbonate effect
KW - cyanobacterium
KW - herbicide-resistance
UR - http://www.scopus.com/inward/record.url?scp=34249833172&partnerID=8YFLogxK
U2 - 10.1007/BF00029814
DO - 10.1007/BF00029814
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AN - SCOPUS:34249833172
SN - 0166-8595
VL - 34
SP - 397
EP - 408
JO - Photosynthesis Research
JF - Photosynthesis Research
IS - 3
ER -