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Plant Physiology 65:735-745 (1980)
© 1980 American Society of Plant Biologists

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Articles

Flash Inactivation of Oxygen Evolution

IDENTIFICATION OF S2 AS THE TARGET OF INACTIVATION BY TRIS 1,2

Wayne D. Frasch3 and George M. Cheniae4

Agronomy Department, University of Kentucky, Lexington, Kentucky 40546

Brief saturating light flashes were used to probe the mechanism of inactivation of O2 evolution by Tris in chloroplasts. Maximum inactivation with a single flash and an oscillation with period of four on subsequent flashes was observed. Analyses of the oscillations suggested that only the charge-collecting O2-evolving catalyst of photosystem II (S2-state) was a target of inactivation by Tris. This conclusion was supported by the following observations: (a) hydroxylamine preequilibration caused a three-flash delay in the inactivation pattern; (b) the lifetimes of the Tris-inactivable and S2-states were similar; and (c) reagents accelerating S2 deactivation decreased the lifetime of the inactivable state. Inactivation proved to be moderated by F, the precursor of Signal IIs, as shown by a one flash delay with chloroplasts having high abundance of F. Evidence was obtained for cooperativity effects in inactivation and NH3 was shown to be a competitive inhibitor of the Tris-induced inactivation. S2-dependent inactivation was inhibited by glutaraldehyde fixation of chloroplasts, possibly suggesting that inactivation proceeds via conformational changes of the S2-state.

3 Present address: Biochemistry Department, University of Wisconsin, Madison, Wisc. 53706.

4 To whom correspondence should be addressed.

1 This work was supported in part by Grant PCM78-07694 from the National Science Foundation to G. M. C. This paper (79-3-153) is published with the approval of the Director of the Kentucky Agricultural Experiment Station.

2 In memory of Bessel, who didn't suffer fools gladly and never compromised his high standards in science.






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Copyright © 1980 by the American Society of Plant Biologists