The status of cysteine residues in the extrinsic 33 kDa protein of spinach photosystem II complexes |
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Authors: | Satoshi Tanaka Keishiro Wada |
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Institution: | (1) Department of Biology, Faculty of Science, Osaka University, Machikaneyama, 560 Toyonaka, Osaka, Japan;(2) Department of Biology, Faculty of Science, Kanazawa University, 920 Marunouchi, Kanazawa, Japan |
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Abstract: | Two cysteine residues of the extrinsic 33 kDa protein in the oxygen-evolving photosystemII (PS II) complexes were found to exist as cystine residues in situ. The 33 kDa protein, when reduced by 2-mercaptoethanol in either the presence or the absence of 6 M guanidine-HCl (Gdn-HCl), could not rebind with the CaCl2-treated PS II complexes, from which the 33 kDa protein was removed, and evolve any oxygen. Two sulfhydryl (SH) groups of the 33 kDa protein were easily reoxidized to a disulfide (S-S) bond by stirring under aerobic conditions with the concomitant regaining of both the binding ability to the CaCl2-treated PS II complexes and the oxygen-evolving activity.The molecular conformation of the 33 kDa protein was examined by circular dichroic (CD) spectrometry in the UV regions to reveal that the conformation in the reduced state was completely different from those of the untreated and reoxidized states. The disulfide (S-S) bond of the 33 kDa protein is thus essential to maintain the molecular conformation required to function.Abbreviations CD
circular dichroism
- Chl
chlorophyll
- DMQ
2,5-dimethyl-p-benzoquinone
- DTNB
5,5 -dithio-bis (2-nitrobenzoic acid)
- EDTA
ethylendiamine-tetraacetic acid
- Gdn-HCl
guanidine-hydrochloric acid
- PS II
photosystem II
- SDS
sodium dodecylsulfate
This paper was presented at the U.S.-Japan Binational Seminar on Solar Energy Conversion, Okazaki, Japan, March 17–21, 1987 |
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Keywords: | disulfide (S-S) bond extrinsic 33 kDa protein Mn chelation oxygen evolution |
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