Fluorescence Decay Kinetics of Wild Type and D2-H117N Mutant Photosystem II Reaction Centers Isolated from Chlamydomonas reinhardtii

We compare the chlorophyll fluorescence decay kinetics of the wild type and the D2-H117N mutant photosystem II reaction centers isolated from Chlamydomonas reinhardtii. The histidine residue located at site 117 on the D2 polypeptide of photosystem II is a proposed binding site for one of two peripheral accessory chlorophylls located in the reaction center complex. The peripheral accessory chlorophylls are thought to be coupled with the primary electron donor, P680, and thus involved in energy transfer with P680. The conservative replacement of the histidine residue with an asparagine residue allows the chlorophyll to remain bound to the reaction center. However, slight changes in the structural organization of the reaction center may exist that can affect the energy transfer kinetics. We show that the D2-H117N mutation causes a shift in the 20-30 ps lifetime component that has been associated with energy equilibration among coupled chlorophylls in the photosystem II reaction center.