Intermolecular and Intramolecular Interactions of the 33‐kDa Protein in Photosystem II

Intermolecular and intramolecular interactions of the extrinsic 33‐kDa protein in photosystem II were investigated by cross‐linking with a water‐soluble carbodiimide as cross‐linking agent. This zero‐length cross‐linker is known to cross‐link the 33‐kDa protein to the chlorophyll‐α‐binding protein CP47 [Bricker, T. M., Odom, W. R. & Queirolo, C. B. (1988) FEBS Lett. 231, 111–117; Enami, I., Kaneko, M., Kitamura, N., Koike, H., Sonoike, K., Inoue, Y. & Katoh, S. (1991) Biochim. Biophys. Acta 1060, 224–2321. In this work, cross‐linking was observed not only to CP47 but also to a small intrinsic subunit. In addition, through the use of a high‐resolution SDS‐gel system, three intramolecular cross‐linked products of the 33‐kDa protein were detected. To search for additional cross‐linking sites that might not be accessible to the cross‐linker in intact photosystem II, the isolated 33‐kDa protein was activated for cross‐linking and subsequently bound to CaCl2‐washed photosystem II. In the complementary experiment, CaCl2‐washed photosystem II was activated, then reconstituted with the 33‐kDa protein. The results of the cross‐linking reactions demonstrated that all carboxylic acid g