The tetranuclear manganese cluster in photosystem II is ligated by one or more histidine residues, as shown by an electron spin echo envelope modulation (ESEEM) study conducted with [(15)N]histidine-labeled photosystem II particles isolated from the cyanobacterium Synechocystis sp. strain PCC 6803 [Tang, X.-S., Diner, B. A., Larsen, B. S., Gilchrist, M. L., Jr., Lorigan, G. A., and Britt, R. D. (1994) Proc. Natl. Acad. Sci. U.S.A. 91, 704-708]. One of these residues may be His332 of the D1 polypeptide. Photosystem II particles isolated from the Synechocystis mutant D1-H332E exhibit an altered S(2) state multiline EPR signal that has more hyperfine lines and narrower splittings than the corresponding signal in wild-type PSII particles [Debus, R. J., Campbell, K. A., Peloquin, J. M., Pham, D. P., and Britt, R. D. (2000) Biochemistry 39, 470-478]. These D1-H332E PSII particles are also unable to advance beyond an altered S(2)Y(Z)(*) state, and the quantum yield for forming the S(2) state is very low, corresponding to an 8000-fold slowing of the rate of Mn oxidation by Y(Z)(*). These observations are consistent with His332 being close to the Mn cluster and modulating the redox properties of both the Mn cluster and tyrosine Y(Z). To determine if D1-His332 ligates the Mn cluster, we have conducted an ESEEM study of D1-H332E PSII particles. The histidyl nitrogen modulation observed near 5 MHz in ESEEM spectra of the S(2) state multiline EPR signal of wild-type PSII particles is substantially diminished in D1-H332E PSII particles. This result is consistent with ligation of the Mn cluster by D1-His332. However, alternate explanations are possible. These are presented and discussed.