Kinetic study of oxygen evolution parameters in Triswashed, reactivated chloroplasts

Tris-washed chloroplasts which have lost the ability to evolve oxygen can be reactivated by the procedure of Yamashita T., Tsuji, J. and Tomita G. (1971) Plant Cell Physiol. 12, 117-126) [7] to give 100 percent of the rate of control chloroplasts in continuous illumination. Furthermore, in flashing light the reactivated chloroplasts exhibit oxygen-yield oscillations of period four that are characteristic of the control. Similar kinetic parameters for intermediate steps in the water-splitting process are observed for the two preparations. We conclude that the reactivation procedure restores the native oxygen evolution mechanism to Tris-washed chloroplasts. A relatively rapid and reversible (0.5 s decay) light-induced component of EPR Signal II is observed upon inhibition of O2 evolution by Tris washing (Babcock G. T. and Sauer, K. (1975) Biochim. Biophys. Acta 376, 315-328) [10]. Reactivated chloroplasts are similar to untreated chloroplasts in that this Signal IItransient is not observed. Manganese, which is released by Tris treatment to the interior of the thylakoid membrane in an EPR-detectable state, is returned to an EPR-undetectable state by reactivation. The reactivation procedure does not require light to restore O2 evolution and EDTA has no effect on the extent of reactivation. These results are discussed in terms of possible mechanisms for manganese incorporation into photosynthetic membranes.