Properties of the low-temperature Photosystem I primary reaction in the P-700-chlorophyll a-protein

The Photosystem I primary reaction, as measured by electron paramagnetic resonance changes of P-700 and a bound iron-sulfur center, has been studied at 15°K in P-700-chlorophyll a-protein complexes isolated from a blue-green alga. One complex, prepared with sodium dodecyl sulfate shows P-700 photooxidation only at 300°K, whereas a second complex, prepared with Triton X-100, is photochemically active at 15°K as well as at 300°K. Analysis of these two preparations shows that the absence of low-temperature photoactivity in the sodium dodecyl sulfate complex reflects a lack of bound iron-sulfur centers in this preparation and supports the assignment of an iron-sulfur center as the primary electron acceptor of Photosystem I.