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

Abstract

Photosystem 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 Ca 2+ , 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 Ca 2+ can be substituted for the 24‐kDa polypeptide in photosynthetic oxygen evolution in Photosystem II particles.