Mar 3, 2004

Biosynthetic Ca2+/Sr2+ exchange in the photosystem II oxygen-evolving enzyme of Thermosynechococcus elongatus

The Journal of Biological Chemistry
Alain BoussacMiwa Sugiura


The thermophilic cyanobacterium, Thermosynechococcus elongatus, has been grown in the presence of Sr2+ instead of Ca2+ with the aim of biosynthetically replacing the Ca2+ of the oxygen-evolving enzyme with Sr2+. Not only were the cells able to grow normally with Sr2+, they actively accumulated the ion to levels higher than those of Ca2+ in the normal cultures. A protocol was developed to purify a fully active Sr(2+)-containing photosystem II (PSII). The modified enzyme contained a normal polypeptide profile and 1 strontium/4 manganese, indicating that the normal enzyme contains 1 calcium/4 manganese. The Sr(2+)- and Ca(2+)-containing enzymes were compared using EPR spectroscopy, UV-visible absorption spectroscopy, and O2 polarography. The Ca2+/Sr2+ exchange resulted in the modification of the EPR spectrum of the manganese cluster and a slower turnover of the redox cycle (the so-called S-state cycle), resulting in diminished O2 evolution activity under continuous saturating light: all features reported previously by biochemical Ca2+/Sr2+ exchange in plant PSII. This allays doubts that these changes could be because of secondary effects induced by the biochemical treatments themselves. In addition, the Sr(2+)-containing PSII has ...Continue Reading

Mentioned in this Paper

Calcium [EPC]
Enzymes, antithrombotic
Cyanobacterium (antigen)
Thermosynechococcus elongatus
Enzymes for Treatment of Wounds and Ulcers
Biochemical Turnover

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