TY - JOUR
T1 - Amino Acid Substitutions in the D1 Protein of Photosystem II Affect Qb” Stabilization and Accelerate Turnover of D1
AU - Ohad, Nir
AU - Amir-Shapira, Dekel
AU - Koikc, Hiroyuki
AU - Inoue, Yorinao
AU - Ohad, Itzhak
AU - Hirschberg, Joseph
N1 - Funding Information:
This work was partially supported by a U.S.A.-Israel BARD grant, 1-1544-88 and by GSF-NCRD Israel, DISNAT 137. We acknowledge also the help of R. Poplavsky in developing the technique for quantitation of D 1turnover.
PY - 1990/5
Y1 - 1990/5
N2 - Isogenic strains of Synechococcus PCC 7942 were genetically engineered so that copy I of the gene psbA was mutated at specific sites. These mutations resulted in replacements of Ser 264 by Gly or Ala and of Phe 255 by Tyr or Leu in the D 1 protein. The mutants were resistant to herbicides inhibiting electron transfer in photosystem II. All mutants exhibited alterations in the stability of QB” as demonstrated by a temperature downshift, to various extents, of the in vivo thermoluminescence emission. Measurements of the light-dependent turnover of D 1 showed a marked decrease in the 11/2 of this protein in the mutants as compared to wild-type, under low to medium light intensities. A correlation was found between the degree of perturbation in the QB~ stability and the rate of acceleration in the turnover of D 1. These data provide a direct evidence for the overlapping binding sites for the plastoquinone B and herbicides in the D 1 protein. In addition these data indicate a close link between QB“ destabilization in reaction center II and the mechanism controlling the light-dependent turnover of D 1. Based on these results and previous work we suggest that destabilization of the semireduced quinone, facilitates a light-induced damage in D 1 which triggers its degradation.
AB - Isogenic strains of Synechococcus PCC 7942 were genetically engineered so that copy I of the gene psbA was mutated at specific sites. These mutations resulted in replacements of Ser 264 by Gly or Ala and of Phe 255 by Tyr or Leu in the D 1 protein. The mutants were resistant to herbicides inhibiting electron transfer in photosystem II. All mutants exhibited alterations in the stability of QB” as demonstrated by a temperature downshift, to various extents, of the in vivo thermoluminescence emission. Measurements of the light-dependent turnover of D 1 showed a marked decrease in the 11/2 of this protein in the mutants as compared to wild-type, under low to medium light intensities. A correlation was found between the degree of perturbation in the QB~ stability and the rate of acceleration in the turnover of D 1. These data provide a direct evidence for the overlapping binding sites for the plastoquinone B and herbicides in the D 1 protein. In addition these data indicate a close link between QB“ destabilization in reaction center II and the mechanism controlling the light-dependent turnover of D 1. Based on these results and previous work we suggest that destabilization of the semireduced quinone, facilitates a light-induced damage in D 1 which triggers its degradation.
KW - D 1 Turnover
KW - Herbicide Resistance
KW - Synechococcus PCC7942
KW - Thermoluminescence
UR - http://www.scopus.com/inward/record.url?scp=0025426220&partnerID=8YFLogxK
U2 - 10.1515/znc-1990-0515
DO - 10.1515/znc-1990-0515
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AN - SCOPUS:0025426220
SN - 0939-5075
VL - 45
SP - 402
EP - 407
JO - Zeitschrift fur Naturforschung - Section C Journal of Biosciences
JF - Zeitschrift fur Naturforschung - Section C Journal of Biosciences
IS - 5
ER -