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The 23 and 17 kDa extrinsic proteins of photosystem II modulate the magnetic properties of the S1-state manganese cluster.

An S1-state parallel polarization "multiline" EPR signal arising from the oxygen-evolving complex has been detected in spinach (PSII) membrane and core preparations depleted of the 23 and 17 kDa extrinsic polypeptides, but retaining the 33 kDa extrinsic protein. This S1-state multiline signal, with an effective g value of 12 and at least 18 hyperfine lines, has previously been detected only in PSII preparations from the cyanobacterium sp. Synechocystis sp. PCC6803 [Campbell, K. A., Peloquin, J. M., Pham, D. P., Debus, R. J., and Britt, R. D. (1998) J. Am. Chem. Soc. 120, 447-448]. It is absent in PSII spinach membrane and core preparations that either fully retain or completely lack the 33, 23, and 17 kDa extrinsic proteins. The S1-state multiline signal detected in spinach PSII cores and membranes has the same effective g value and hyperfine spacing as the signal detected in Synechocystis PSII particles. This signal provides direct evidence for the influence of the extrinsic PSII proteins on the magnetic properties of the Mn cluster.