Calcium ions can be substituted for the 24-kDa polypeptide in photosynthetic oxygen evolution

AbstractPhotosystem II particles were prepared from spinach chloroplasts with Triton X-100, and treated with 1.0 M NaCl to remove polypeptides of 24 kDa and 18 kDa and to reduce the photosynthetic oxygen-evolution activity by about half. Oxygen-evolution activity was restored almost to the original level with 10 mM Ca2+, in a similar manner to the rebinding of 24-kDa polypeptide. Other cations such as magnesium, sodium and manganese ions could not restore any oxygen-evolution activity. These observations, together with a kinetic analysis, suggest that Ca2+ can be substituted for the 24-kDa polypeptide in photosynthetic oxygen evolution in Photosystem II particles