We have characterised the electron-transfer properties of the D1/D2/cytochrome b-559 complex using EPR spectrometry. The complex can transfer electrons to silicomolybdate and ferricyanide at cryogenic temperatures. In the presence of silicomolybdate or ferricyanide, two chlorophyll cation radicals were observed from P680+ (0.8 mT) and monomeric Chl (1.0 mT). Reduction of silicomolybdate was detected as a 2.7 mT signal at g = 1.942. A radical attributed to a tyrosine cation radical (D+/Z+) was also observed in a small percentage of centres.
